A. Technical Bulletin No. 930

In 1946, USDA issued Technical Bulletin No. 930, "Home Canning Processes for Low-Acid Foods" (Toepfer et al, 1946), which reported the first scientifically developed recommendations for home canned foods. Heat-penetration data for meats, poultry and vegetables were obtained in experiments with home-canning procedures and equipment. These were then combined with thermal death time data for calculating thermal process schedules. Inoculated packs were used to check the calculated process times.

The publication contains a lengthy discussion of the general method for calculating process schedules, summarizing the way Ball developed this concept in 1928 (Toepfer et al, 1946). Thermal death time curves for organisms are plotted on the logarithmic scale of semilog paper. The study utilized Z and F values from Esty and Meyer (1922) for C. botulinum which were generally accepted by that time. From their data, values of F = 2.78 (time at 250F to destroy a standard spore suspension) and Z = 18 were derived. The lethal rate (F/t), or ratio of time in minutes required to destroy an organism at 250F to the time required to destroy it at the given temperature, can be found from this thermal death time curve (Toepfer et al , 1946).

A lethality curve is a plot of lethal rates (F/t) over time during heating (fh) and cooling (fc). The area under the lethality curve represented the total lethal value of (F0) of the entire process. An F0 value equivalent to or higher than the F value of the spoilage or test organism to be destroyed was recognized as an adequate process (Toepfer et al, 1946).

Process values for a minimum of three process replications were used to plot a lethality curve. Process times for specified F0 values could be determined from this curve for any spoilage organism when Z = 18. It was observed that the relationship between process times and process values (F0) in the ranges being investigated was approximately linear. Therefore, the linear regression line (Yr = a + bx) was fitted to the f0/process time-data for each product and the standard error of estimate computed. In this regression equation, x equals the process time; Y equals the process value; a equals the constant locating the line vertically; and, b equals the slope of the line (Toepfer et al, 1946).

A parallel line constructed at a distance of 2.6 times the standard error of estimate below the computed regression line allowed a probability of 0.005 that a container would yield an F0 value less than that of the lower line. A minimum safe process was considered as the process time read from the lower limit at a given F0 value. This method assumes normal distribution of the F0 values and allows for a spoilage rate of 0.5 percent, or one container in every 200 (Toepfer et al, 1946).

Still imprecise bacteriological data available at that time limited process computations. Data of bacterial loads and thermal-death times would err, if at all, in favor of longer-than-necessary processes. However, processes determined for low-acid foods were at least adequate for destroying C. botulinum spores. Research by Townsend et al (1938) indicated variations in Z-values in food media were both greater and lesser than the ideal value for his organism in neutral buffer as determined by Esty and Meyer (1922). The most widely accepted practice was to use a Z value of 18 for lack of better information (Toepfer et al, 1946).

Two safety factors - a more heat resistant test organism and the inoculated pack technique - were eventually adopted to compensate for the 0.5 percent spoilage rate allowed in theoretical calculations. The test organism, P.A. No. 3679, had been shown to be more heat resistant than spoilage organisms commonly isolated from low-acid foods (Townsend et al, 1938; Tischer and Esselen, 1945). The concentration of inoculum (30,000 spores per pint for meats and 10,000 spores per pint for vegetables) and their placement at the slowest heating point offered additional safety factors. In this study, inoculated packs followed the design of Williams (1940). Inoculated packs were run on pork in quart jars and vegetables in jars. The data were applied to meats and vegetables in other sizes and types of containers (Toepfer et al, 1946).

Temperatures for this research were measured by copper-constant thermocouples placed at the slowest-heating region in the so-called cold spot in the containers. The initial temperature was defined as the temperature attained by the food when the temperature in the pressure canner reached 240F and process time began. Filling and sealing temperatures of foods were recorded separately.

Full canner loads were processed each time, using aluminum pressure canners which held 16 pints, 7 quarts, 16 No. 2 metal cans, or 10 No. 2½ or 3 cans. All but quart jars were stacked in two tiers. Jars or cans with mounted thermocouples were distributed to the center and side in each tier. Sealed canners were exhausted 10 minutes after attaining 212F. Process time was counted when the pressure canner reached 240F. Pressurized canners with glass jars were cooled at room temperature until 212F was reached, when jars were removed and allowed to continue cooling at room temperature. With metal cans, pressure was mechanically released from canners at the end of process time. Cans were removed immediately and immersed in cold water. Temperatures of all food containers were recorded until they dropped below 190F.

Preliminary heat penetration data were used for choosing processes for inoculated packs wherein the shortest process yielded gross spoilage after incubation ( to check the viability of the test suspension). The intermediate and longest process values were chosen to yield some and no spoilage, respectively. For each of the three processes, the pack consisted minimally of 24 inoculated and 12 non-inoculated (control) jars. Jars were incubated 90 days at 86F for vegetables. Non-spoiled jars of vegetables were subcultured to check for survival of the test organism. Meats were held an additional 18 months at room temperature after a four-month incubation at 98.6F.

The experimentally-determined process values for pork were all within the range of the mean minus 2.6 times the standard deviation which yielded a lower limit of F = 5.1. Therefore, this was the lower limit chosen for process calculations and was understood to provide a wide margin of safety for C. botulinum when F = 2.8. The process values for meat and poultry as determined by this research are presented below (Toepfer et al, 1946):

The process times for asparagus, snap beans, beets, carrots, okra, pumpkin, spinach, squash and sweet potatoes were chosen to yield F values at 5.0. The inoculated pack data had been used to arrive at this value and also indicated that the test organism was more resistant in lima beans, corn and peas. The F values necessary for these three products were observed to be 9.3, 12.8 and 8.5, respectively. The inoculated pack data is shown in Table 8 below (Toepfer et al, 1946) and the resulting process values, calculated process times and recommended process times are shown in Table 9 (Toepfer et al, 1946).

The results of this research may be summarized as follows:

1. The new process times were compared to the process schedules which USDA had been recommending for vegetables in AWI-93 and Farmers' Bulletin No. 1762. For every vegetable product, processes for vegetables in pints could be shortened from those previously recommended. For quarts, however, longer processes were derived for a few products and overall process reductions were not as great as for pints. Lower initial temperatures and larger error estimates were observed for quart containers.
2. The cooling period contributed variably to the lethal value of the process, and depended on the type of container (Toepfer et al, 1946):

   Table 10 Lethality of the Cooling Period
   Container Pint glass jar Quart glass jars No. 2 tins No. 2½ tins	Fc (% of Fo) 50 36 15 11

   In general, the cooling period for glass containers contributed substantially to the lethal value of the total process. This was not reflected, however, in shorter processing times. The discrepancy was attributed to the fact that initial temperatures in tins were higher than for glass containers. These containers were exhausted and sealed at 170F or above. Glass containers were packed hot, but not exhausted before processing.

3. The new process times for meats were compared to those USDA had been recommending. The process temperature could be reduced from 250F to 240F for all products. Also, times for all meat products were reduced, except for chicken.
4. Since processes were based on P.A. No. 3679, researchers speculated that these were more severe than necessary to destroy the normal microbial load on vegetables and meats as prepared for home canning; therefore, further reductions in home-canning process times would still be possible. They further acknowledged, however, more precise data on heat resistance and slopes of thermal-death-time curves for food spoilage organisms were needed. These conclusions set the stage for subsequent research carried on at USDA during the next decade.

The new processes developed by Toepfer et al (1946) were first released in AWI-110, "Home Canning of Meat" (USDA, 1945b) and in two publications titled "Home canning of Fruits and Vegetables": AIS-64 (USDA, 1947e) and Home and Garden Bulletin No. 8 (USDA, 1947f). Except for minor changes in 1957, these have remained as the current recommendations. The methods of preparation and types of packs were specified in TB 930. These have also remained almost identical through the years, with the addition of a few products also occurring between 1947 and 1957.

The Tables 11, 13, and 14 indicate the process recommendations as released on the basis of the research reported in TB 930 and the changes that occurred in subsequent publications. The last changes made in fruit and vegetable processing schedules occurred in 1957 in Home and Garden Bulletin No. 8 (USDA, 1957a), and for meats in Home and Garden Bulletin No. 6 (USDA, 1951c). The nature of changes included processing times for some products, addition of raw-pack recommendations, and scientifically determined, calculated processes for acid foods. Some changes can be traced directly to subsequent research reports. However, other changes and recommendations cannot be substantiated. Yet, based on the work of Toepfer et al (1946) it appeared that the scientific method of process calculations had been fully accepted in USDA by this time.

Tables 11, 13, and 14 also indicate origins for some changes since TB 930, which are discussed below. Nondocumented changes are also summarized and discussed.

Notes

1. The origins of these recommendations in Technical Bulletin 930 (Toepfer et al, 1946), with the exception of No. 2 cans, wet sweet potatoes, which were to be processed 75 min., according to TB930. The origin for this change is unknown.
2. These recommendations remain the current processes, as in Home and Garden Bulletin No. 8 (USDA, 1977).

• (a) Origin is unknown.
• (b) Desrosier, N.W. and W.B. Esselen. 1950. Heat penetration and processing studies on home-canned corn, hominy, pork and beans, and potatoes. University of Massachusetts Agricultural Experiment Station Bulletin 456.
• (c) Cover, S., Shrode, M.C. and H. Reynolds. 1956. The evaluation of processing times for raw-pack canning of some low-acid vegetables at home. Food Research 21:405.
• (d) Dawson, E.H., Gilpin, G.G., Warren, H.W. and E.W. Toepfer. 1953. Canning snap beans precooked and raw pack. Journal of Home Economics 45:165.
• (e) Cover, S., Smith, A.B., Shepperd, M.P. and E.G. Crawford. 1948. Development of safe methods for canning blackeye peas at home. Agriculture and Mechanical College of Texas Agricultural Experiment Station Bulletin 707.

  C. Origins of Processes for Low-Acid Vegetables

  Asparagus and Beets

  Two USDA publications, AIS-64 and HG-8, were issued in July of 1947, and the recommended process schedules for asparagus and beets were inconsistent. The process times recommended in AIS-64 were identical to those derived in the research report, TB 930, with one exception. The process time for wet sweet potatoes packed in No. 2 cans was decreased from 75 to 70 minutes after TB 930. The reason for this change was not located in the literature reviewed.

  Processing times for asparagus and beets in glass quart jars were lower in HG-8 than in AIS-64. Some explanation for these processing discrepancies was obtained from copies of Tri-annual Progress Reports from the Food and Nutrition Division (USDA, 1947b; 1947d) and a letter written by the Division's bacteriologist, Howard Reynolds (1949).

  In 1944-45, the original heat penetration data on pints of beets and asparagus were collected by the Food and Nutrition Division, while the Housing and Household Equipment Division collected the data on quart packs of these two products. It was later discovered that the pints had been packed as sliced beets and cut asparagus, while the quarts had been packed as diced beets and asparagus stalks. Therefore, in 1947, the Food and Nutrition Division collected data on hot-packed quart jars of sliced beets and cut asparagus (Reynolds, 1949). Calculations from this latter data indicated that processes of 40 minutes at 240F would yield F0 values of 5 for both these products (USDA, 1947b). The new recommendations were apparently released immediately. The process time for quart packs of beets still contained a discrepancy, as it was 45 minutes rather than 40 minutes. No explanation for this could be found in the literature.

  After these experiences, it was concluded that further studies were needed to evaluate the relationship between pack style and initial temperature to process values. The cold spot location in quart jars of diced beets was determined at the BHNHE in 1947 (USDA, 1947d). Process values for beets and asparagus were further studied at the Massachusetts Agricultural Experiment Station in a cooperative project completed in 1950. Tables of heat penetration data are missing from the literature reviewed; however, these studies appear to be the basis for reductions in process times for beets and asparagus which occurred in 1957 in HG-8 (USDA, 1957a) and remain today.

  Blackeye Peas

  The process recommendations for canning blackeye peas were developed through research conducted by the Texas Agricultural Experiment Station. This research was reported in 1948 in Texas Agricultural Experiment Station Bulletin 707 (Cover et al, 1948). The experimental method as reported in TB 930 was essentially used in this research. However, fill-weight and headspace were standardized. Heat penetration in raw and hot-packs were measured continuously by thermocouples and inoculated packs with P.A. No. 3679 were conducted. Process times were determined using the linear regression equation and standard error of estimate. Minimum F values of 8.0 were adopted for adequate processes for blackeye peas. However, calculated processes were rounded off to the nearest five-minute interval in determining recommended process times. In the case of hot-pack pints, this meant dropping one minute off the calculated time. Process values are usually rounded up.

  Another concern which arises from these data is indicated by comparison of raw- and hot-packs. The calculated process times were lower for raw-packs than hot-packs for both pints and quarts. However, the nature of this product indicates that heat penetration should be more rapid in a hot pack. The only logical explanation for these data is that the fill-weight used in the hot pack was too high and resulted in a reduced rate of heat penetration. The calculated process time of 33 minutes for raw-pack quarts of blackeye peas was raised to 40 minutes instead of 35 minutes for the recommended schedule in order that the same time could be offered for both raw and hot packs.

  Dry Beans, Hominy, Potatoes

  The recommendations for hominy, whole and diced white potatoes, pork and beans, and oven-baked beans were developed at the Massachusetts Agricultural Experiment Station in a cooperative project with the BHNHE, USDA. The results were reported in Massachusetts Agricultural Experiment Station Bulletin 456 (Desrosier and Esselen, 1950). Thermal death time studies with P.A. No. 3679 were conducted on these food substrates. Cold points in containers of uniform fill-weight were also determined. Process times were determined by three methods based on individual heat penetration data from a minimum of 12 containers and three replications.

  The three methods of process determination were inoculated pack studies, statistical calculations with the linear regression line and standard error of estimate, and composite data from slowest heating and fastest cooling jars. Processes in excess of those required for sterilization were determined to be essential for beans and hominy in order to provide the desired quality in the finished product (Desrosier and Esselen, 1950). The sterilizing values, selected from early data, were F values of 9 for hominy and 11 for Irish potatoes and 12 for pork and beans and baked beans (USDA, 1947d).

  Development of Raw Packs for Low-Acid Vegetables

  Citing the reason that raw-pack methods were easier than hot-pack procedures, Cover et al (1948) developed processing schedules for raw-packs of blackeye peas at the same time hot-pack schedules were determined. It was not until 1956, however, that raw-pack schedules for other vegetables were recommended as a result of another cooperative project between the BHNHE and the Texas Agricultural Experiment Station (Cover et al, 1956). Hot packs, previously favored for more solid packs, had become implicated in causing excessive quality losses in color, flavor, texture and nutrient retention.

  Thiessen (1949) reported on the effect of home-canning procedures on vitamin C content in snap beans, tomatoes, peaches and pears. The extent of the vitamin C loss in canned snap beans differed according to the method of product preparation. Losses were higher when there was a larger amount of cut tissue surface exposed. Blanching and scalding had the most detrimental effect on vitamin C loss. In three different style packs, however, losses of vitamin C were reduced 18 to 37 percent for raw packs. Vitamin C losses in canned tomatoes were about 29 percent for a raw pack and 37 to 42 percent for the hot pack. All canned pears were practically devoid of vitamin C; if ascorbic acid was added, 58 percent was retained through processing. Retention of added ascorbic acid was greater in canned peaches. The latter two fruits received only raw-pack treatment. The ascorbic acid also notably improved both color and flavor in these products. No data on the sterilizing values of the raw and hot processes were reported; however, maximum thermometers recorded temperatures of 240F in both raw and hot packs with similar processing times.

  Dawson et al (1953) reported on the nutrient retention in raw- and hot-packed snap beans. Heat penetration tests were used to determine that 20 minutes at 240F provided equivalent sterilizing values for both raw- and hot-pack pints of home-canned snap beans. Data from these tests were not reported, however. The raw-pack method was found to result in higher palatability (color, flavor and texture) scores than the hot-pack. The retention of ascorbic acid was significantly higher in liquid and beans for the raw pack. The proportion of liquid was higher in the raw pack, too, and chemical analyses showed no real differences in the drained solids from either method. Thiamine content of the drained beans was higher for the hot-pack method.

  The majority of the recommended process times for raw-packed vegetables were determined at the Texas Agricultural Experiment Station, in a cooperative project with the BHNHE (Cover et al, 1956). Many processing variables reflecting adverse conditions which may be practiced in the home were incorporated into the research project. Data from other studies were used to locate "cold points" near the geometric center of conduction-heated products, and on the longitudinal axis near the jar bottom of convection-heated foods (Jackson and Olson, 1940; Esselen and Tischer, 1945; Townsend et al, 1949; Desrosier and Esselen, 1950).

  Process values were estimated by 1) the regression method with F values of individual jars as described in TB 930, and 2) construction of lethality curve using individual jar temperatures, as described in TB 930 and by Cover et al (1948). Process times were designed to yield sterilizing values equal to those for hot packs. Several different treatments of the data, including a composite of temperature data from the fastest heating-slowest cooling jars, were used to estimate process times which differed only by 0.5 minute (Cover et al, 1956).

  Previous studies (Cover et al, 1948; Dawson et al, 1953) indicated that similar processing times for raw- and hot-packs of convection heating low-acid foods should yield comparable sterilizing values. Since some discrepancies were noted in products where the times should have been similar, the raw-pack data of Cover et al (1956) were compared with those of hot packs determined earlier (Toepfer et al, 1946). In several cases, the raw-pack times were longer than those recommended for hot packs. It was noted that heat penetration data were more variable in hot packs than raw packs. However, average lethalities were in agreement. Fill-weights were standardized only in raw-pack studies which may have accounted for this discrepancy.

  A study of data for raw- and hot-pack vegetables appears to have been the basis for changing some recommendations. Changes included process times for hot-pack pints and quarts of lima beans, hot-pack pints and quarts of carrots and the No. 2½ can of hot-pack peas (USDA, 1957a). Processes for hot-packed cream-style corn and summer squash were not changed. Data collected on these conduction-heated products indicated that their temperatures when filled into jars influenced process schedules.

  Recommended raw-pack process schedules were lower than the calculated process for cream-style corn in pints, peas in quarts and pints and summer squash in quarts (Cover et al, 1956; USDA, 1957a). Specifically, the schedule for raw-packed pints of whole kernel corn was 11 minutes shorter in the 1957 USDA recommendation than for the calculated process (Cover et al, 1956). The following table lists schedules calculated by Cover et al (1956) for raw- and hot-packs and the recommendations published in 1957 by USDA in HG-8 (USDA, 1957a):

  Table 12
  Comparison of Calculated and Published Processes for Vegetables

  Food	Suggested Process Requirements (F)	Container Size	Calculated processing time at 240F		Recommended processing time at 240F (1957)
  			Raw Pack (minutes)	Hot Pack (minutes)	Raw Pack (minutes)	Hot Pack (minutes)
  Beans, lima	9.3	Pints Quarts	37 45	32 57	40 50	40 50
  Carrots	5.0	Pints Quarts	24 30	19 25	25 30	25 30
  Corn, cream style	12.8	Pints	96	83	95	85
  Corn, whole kernel	12.8	Pints Quarts	66 84	54 82	55 85	55 85
  Peas, English	8.5	Pints Quarts	41 43	38 41	40 40	40 40
  Squash, Summer	5.0	Pints Quarts	24 31	28 37	25 30	30 40

  Cover et al (1956) reported that the selected sterilizing values for some products were excessive, particularly for whole corn. Apparently, they felt the F0 values applied to raw-packed home-canned foods contained excessive margins of safety. This philosophy was based on thermal-death-time data of P.A. No. 3679 spores in food substrates published by Sognefest et al (1948), Reed et al (1951) and Reynolds et al (1952). Accordingly, a line-project interim report from BHNHE (USDA, 1952) indicates that schedules were revised for raw and hot packs of each low-acid product based on re-calculations from composite slowest heating-fastest cooling curves collected in earlier studies, and thermal-death-time data in the forementioned studies.

  D. Origins of Processes for Meats and Poultry

  Most of the recommended process schedules for meats and poultry originate from the research published in TB 930. There is indication in the publication that meats were packed raw and hot in four sizes of containers; however, the data for each of these products are not presented in the research report. This study apparently is the origin for hot- and raw-packs of cut-up beef, pork, and poultry.

  Table 13
  Origins of Home Canning Processes for Meats and Poultry

  Product	Recommended Process Time (Minutes) at 240F
  	1946 AWI-110	1951* HG-6
  CUT-UP MEAT (a) Hot Pack PT QT 2 CAN 2½ CAN Raw Pack PT QT 2 CAN 2½ CAN	. . 75 90 65 90 . . 75 90 65 90	. . 75 90 65 90 . . 75 90 65 90
  GROUND MEAT (d) Hot Pack PT QT 2 CAN 2½ CAN Raw Pack PT QT 2 CAN 2½ CAN	. . 75 90 65 90 . . - - 100 135	. . 75 90 65 90 . . - - 100 135
  SAUSAGE (d) Hot Pack PT QT 2 CAN 2½ CAN	. . 75 90 65 90	. . 75 90 65 90
  CORNED BEEF (d) Hot Pack PT QT 2 CAN 2½ CAN	. . 75 90 65 90	. . 75 90 65 90
  MEAT-VEGETABLE STEW (b) Hot Pack PT QT 2 CAN 2½ CAN	. . - - - -	. . 60 75 40 45
  HEART & TONGUE (d) Hot Pack PT QT 2 CAN 2½ CAN	. . 75 90 65 90	. . 75 90 65 90
  SOUP STOCK (d) Hot Pack PT QT 2 CAN 2½ CAN	. . 20 25 20 25	. . 20 25 20 25
  CUT-UP POULTRY (a) Hot Pack w/bone PT QT 2 CAN 2½ CAN Hot Pack w/o bone PT QT 2 CAN 2½ CAN Raw Pack w/bone PT QT 2 CAN 2½ CAN Not exhausted (d) QT Raw Pack w/o bone PT QT 2 CAN 2½ CAN	. . 65 75 55 75 . . 75 90 65 90 . . 65 75 55 75 . . - . . 75 90 65 90	. . 65 75 55 75 . . 75 90 65 90 . . 65 75 55 75 . . 80 . . 75 90 65 90
  GIBLETS (d) Raw Pack w/o bone PT 2 CAN	. . 75 65	. . 75 65
  RABBIT (d)	As chicken	As chicken
  PORK & BEANS W/SAUCE (d) PT QT 2 CAN 2½ CAN	. - - - -	. 65 75 65 75
  PORK & BEANS W/PORK (c) PT QT 2 CAN 2½ CAN	. - - - -	. 80 100 95 115

  Notes
  *These schedules from Home and Garden Bulletin No. 6 (USDA, 1951c) remain as the current recommendations, with the deletion of pork and beans products, in Home Canning of Meat and Poultry, Home and Garden Bulletin No. 106 (USDA, 1966).

  Origins of Recommendations

  • a) Toepfer, E.W., Reynolds, H., Gilpin, G.L. and K. Taube. 1946. Home canning processes for low-acid foods. USDA Technical Bulletin No. 930.
  • b) USDA. 1947b. Food and Nutrition Division Tri-annual Progress Report, Project No. b1-16-7. April-July.
  • c) Desrosier, N.W. and W.B. Esselen, 1950. Heat penetration and processing studies on home-canned corn, hominy, pork and beans, and potatoes. University of Massachussets Agricultural Experiment Station Bulletin 456. These items were removed from this series in the 1966 version, which became the Home and Garden Bulletin No. 106.
  • d) Origin is unknown.
  Vegetable-Beef Stew
  Reference is made to the development of recommendations in a 1947 Tri-annual Progress Report from the Food and Nutrition Division (USDA, 1947b). The schedules were developed from heat penetration data, and confirmed by inoculated pack studies. The methods outlined in TB 930 were utilized in collecting data. The recommendations were summarized as follows:
  "Since spoilage among inoculated packs caused by survival of the test organism occurred with the process having an average F0 value of 8.5 and the value for the next longer process was 8.8, home canning processes for the vegetable-meat stew should be designed to yield an F0 value of 9. Calculations from the heat penetration data, with allowances for observed variability, indicate that the following processing times at 240F should be adequate to yield the required sterilizing value:

  pint jars quart jars No. 2½ tins

  60 minutes 75 minutes 45 minutes

  Preparation and packing procedures used in canning vegetable-beef stew during the above studies are outlined in the annual progress report for the period April 1, 1946 to March 31, 1947. The vegetable-meat mixture was packed into containers cold. Jars were processed after packing without preheating. Tins were exhausted to a center temperature of at least 170F before sealing and processing and were, therefore, at a relatively high initial temperature. This exhaust given the tins probably accounts for the considerably shorter processing time required for No. 2½ tins as compared with quart and pint packs which were placed in the cooker cold."
  Pork and Beans, Baked Beans

  The recommendations for canning pork and beans with sauce and baked beans with pork were included in Home and Garden Bulletin No. 6 (USDA, 1951c). They were removed when the series changed to USDA Home and Garden Bulletin No. 106 issued in 1966. The processes had been developed during 1947-48 at the Massachusetts Agricultural Experiment Station. The research was described in Massachusetts Agricultural Experiment Station Bulletin 456 (Desrosier and Esselen, 1950), which has been discussed under origins of low-acid recommendations.

  Other Products

  A search of the available literature offers no data or direct reference for the development of processes for ground meat, sausage, corned beef, heart and tongue, soup stock, giblets, and rabbit. The processes for all except soup stock and rabbit are related to those of cut-up meat. Schedules for rabbit and chicken are the same. Cover et al (1943) had done some research with raw-packed ground meat in cans and calculated processes based upon heat penetration data. The schedule for No. 2 cans was calculated to be 100 minutes at 10 psig, which is the current recommendation (USDA, 1966). However, at the time of the research, it was considered impractical and recommendations were made for 15 psig only. Some references in progress reports from the BHNHE ( USDA, 1944b, Jan. - Mar.) indicate that work with ground meat (sausage) continued, but no data or specific origins or process recommendations can be found.

  F. Origins of Processes for Acid Foods

  According to a plan of work for the line project, "Home Canning Methods: Bacteriological, food preparation and nutritive value studies" (USDA, 1945d), a three- to five-year project was approved in March, 1945. This project included the goal of determining minimum safe and spoilage processes for acid foods. However, results of the acid food studies are difficult to trace. An incomplete series of progress reports on this and subsequent BHNHE projects cites some research toward the development of process recommendations for acid foods.

  An annual progress report for the year ending March, 1945 (USDA, 1945a) describes studies of various styles of raw- and hot-packed tomatoes. Tests regarding ascorbic acid changes during canning were also conducted. The results of these tomato studies will be discussed in a section devoted to this product.

  Research on processing acid foods was conducted in cooperation with the Massachusetts Agricultural Experiment Station. A 1946 annual report from the Food Technology Department at Massachusetts State College (1946a) reports preliminary heat penetration data for rhubarb, strawberries, sour cherries, raspberries, blueberries, peaches, applesauce, tomatoes and tomato juice. Data were collected for processing temperatures at 212F and 1, 5 and 10 psig, but fh values were calculated on a basis of 212F retort temperature and an F value of 1.0. Conclusions included: 1) initial temperature is very important in processing fruits because of the low lethal rate of the organisms involved; 2) the current recommended processes were higher than required in some cases; 3) more information was needed on spoilage organisms of home-canned fruit.

  The BHNHE was also collecting data for acid fruits (USDA, 1946b, Apr. - July). The researchers at USDA were obtaining heat penetration data for small fruit (sour cherries or berries), large fruit (plums and peaches) and applesauce. Jars were inoculated with a suspension of orchard soil because no organisms with sufficient thermal resistance for potential spoilage had been reported. It was decided that acid products, like cherries, were easy to sterilize with respect to aciduric organisms.

  Experiments were designed to test the proposal that with hot packs, the major objective of the process was to sterilize the closure. Lids were contaminated with a butyric anaerobe and soil suspension and were then used on hot-packed cherries. Cherries were inoculated with 121 x 10 (to the 7th power) cells of the most resistant yeast studied. The butyric anaerobe survived heating to the boiling point, but not after 5 or 10 minutes of boiling. Nonaciduric organisms survived the 10 minutes of boiling. The inoculated yeast was not recovered from any of the jars; therefore, it was apparently controlled by heating just to the boiling point. Unfortunately, the species of yeast and organisms used for inoculations were not delineated in this report.

  If culture numbers did not change over the years, an earlier report (USDA, 1944b, July-Sept.) indicates that the butyric anaerobe used for inoculating the cherries was some strain of the Clostridium species identified as C. multifermentans. This name is no longer recognized in the current edition of Bergey's Manual of Determinative Bacteriology (Buchanan and Gibbons, 1974).

  The 1946 annual report from Massachusetts Agricultural Experiment Station (Mass. State College, 1946b) reported summaries of some heat penetration data and the fact that molds isolated from rhubarb and strawberries survived 20 minutes and 15 minutes of boiling, respectively. Work continued at the BHNHE with the palatability of canned fruits and tomatoes and heat penetration studies of raw- and hot-packed fruits processed at 212F to a center temperature of 200 F (USDA, 1946b, Aug.-Nov.).

  Table 14
  Origins of Home Canning Processes for Acid Foods

  Product	Recommended Process Time (Minutes) at 240F
  	1947 HG-8 (1)	1957 HG-8 (2)
  APPLES Hot Pack PT QT 2 CAN 2½ CAN	. . 15 15 10 10	. . 15 20 10 10
  APPLESAUCE Hot Pack PT QT 2 CAN 2½ CAN	. . 10 10 10 15	. . 10 10 10 10
  APRICOTS (d) Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . 25 35 25 35 . . 20 20 25 35	. . 25 30 30 35 . . 20 25 25 30
  BEETS, PICKLED PT QT	. 30 30	. 30 30
  BERRIES Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . 20 20 15 20 . . 15 15 15 20	. . 10 15 15 20 . . 10 15 15 20
  CHERRIES Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . - - - - . . 15 15 15 20	. . 20 25 20 25 . . 10 15 15 20
  FRUIT JUICES Hot Pack PT QT 2 CAN 2½ CAN	. at 180F 20 20 20 20	. . 5 5 5 5
  FRUIT PUREES Hot Pack PT QT 2 CAN 2½ CAN	. at 180F 20 20 20 20	. . 5 5 5 5
  PEACHES & PEARS Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . 25 35 25 35 . . 20 20 25 35	. . 25 30 30 35 . . 20 25 25 30
  PLUMS Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . - - - - . . 15 15 15 20	. . 20 25 15 20 . . 20 25 15 20
  RHUBARB Hot Pack PT QT 2 CAN 2½ CAN	. . 10 10 10 10	. . 10 10 10 10
  TOMATOES Raw Pack PT QT 2 CAN 2½ CAN Hot Pack PT QT 2 CAN 2½ CAN	. . 35 45 45 55 . . 10 10 - -	. . 35 45 45 55 . . 10 10 10 10
  TOMATO JUICE Hot Pack PT QT 2 CAN 2½ CAN	. . 15 15 15 15	. . 10 10 15 15
  SAUERKRAUT Hot Pack PT QT 2 CAN 2½ CAN	. . 25 30 20 30	. . 15 20 20 25
  STRAWBERRIES Hot Pack PT QT 2 CAN 2½ CAN	. . 15 15 10 15	. . - - - -

  Notes
  1. The process times for fruits and acid foods varied somewhat in the publications preceding this one. However, because changes occurred in the methods of determining process recommendations about this time, this is the first process schedule shown.
  2. These are the current recommendations printed in Home and Garden Bulletin No. 8 (USDA, 1977) with the deletion of sauerkraut from this series having occurred after 1957.
  The heat resistance of organisms causing spoilage in acid foods was also studied further at Beltsville and at the University of Texas. However, organisms they studied consistently showed little heat resistance (USDA, 1947a).

  The 1948 annual report from the Massachusetts Agricultural Experiment Station reported calculated process times for hot-packed fruits canned at 212F (University of Massachusetts, 1948a). These process values were based on data from the slowest heating-fasting cooling characteristics in pint and quart glass jars. An F0 value of 1.0 was considered a sufficient process, and was based on the butyric anaerobe with F212 = 1.0. A cold point temperature of at least 190F was also studied.

  Relevant heat penetration data were presented in a later progress report (University of Massachusetts, 1948b). Still later, a meeting was held with Dr. Esselen of the University of Massachusetts to consider the status of the work with acid foods (USDA, 1948c). It was concluded, on a basis of available bacteriological data, that 1) heat penetration data on fruits could be used to determine processing times yielding sterilizing values of F212 = 1.0, based on an assumed thermal death time curve with a slope of Z = 17, or 2) adequate sterilization was achieved when center container temperatures reached 190F. It was further decided that recommended processing times would be based on studies which yielded the longest schedule. Although inoculated pack studies at that time indicated less processing was needed, schedules should be adequate to inactivate enzymes and provide adequate exhaustion of air.

  Many current recommendations for acid foods were evidently determined from the data reported in these studies. However, data needed to suggest a few current recommendations are missing or the data conflict with available information. Due to the sporadic nature of the reports and available literature, it is difficult to assign specific origins to most of the processes.

  F. 1982 Meeting with National Food Processors Association and USDA, AES and ARS Representatives

  As part of the process of assessing and tracing the origins of USDA home-canning recommendations, a meeting was held at offices of the National Food Processors Association (NFFA) in Washington, D.C., on August 26, 1982. In attendance at the meeting were Cleveland Denny and Lloyd Hontz representing NFPA, Dr. Milton Baldauf of USDA, AES, Dr. Reginald Handwerk of USDA, ARS, and Dr. Gerald Kuhn, Extension Food Scientist, and Elizabeth Andress, Research Assistant, of The Pennsylvania State University. The USDA process schedules of concern for home-canned vegetables, fruits and meats were reviewed and possible solutions for remaining issues were discussed.

  In the process, knowledge relevant to sterilization of glass jars, venting of pressure canners and newer steam canning equipment was also shared. The review of process recommendations for vegetables was lengthy and the following list constitutes the topics of greatest concern or remaining issues: asparagus, beets, cream-style corn, whole kernel corn, mushrooms, peas, strained pumpkin, spinach, summer squash, tomatoes and acidified products. The issues of concern were partially determined by examining original data which had been located for some products in relation to recent knowledge learned in he canning industry. Other issues were identified by comparing suspect home canning processes with commercial schedules as provided in Bulletin 26-L published by the National Food Processors Association (1982). The issues and relevant conflicts with current knowledge are summarized in he following section.

  ISSUES REMAINING ABOUT PROCESS ORIGINS

  A. Asparagus and Beets

  The currently recommended process times for these products home-canned in glass jars are 1) pints, 25 minutes and quarts, 30 minutes for asparagus, raw or hot pack, and 2) pints, 30 minutes and quarts, 35 minutes for hot-packed beets. These two products are considered together because they were both the subjects of early scrutiny due to discrepancies in product preparation at the time of original data collection. Changes occurred in the recommended process times for quart jars between IS-64 and HG-8. The latter recommendations are the current ones.

  Research summaries indicate that these changes were due to research which improved upon the methods of data collection and analysis and controlled fill-in weights and styles of cut vegetables. However, no heat penetration data are available which are compiled with a narrative explanation describing decisions which were made. Those records (USDA, 1951a) summarizing changes in process times which were to be released are not consistent with the schedules which appeared in subsequent publications (USDA, 1957a). The latest reports for these products (USDA, 1951a), lacking heat penetration data, stated that sliced beets required longer processing than other cuts, but current recommendations make no distinction between sliced, whole or quartered beets. Therefore, it has not been possible to completely substantiate the origins for current recommendations for these products.

  B. Spinach

  Numerous references can be found in annual and tri-annual progress reports from files at USDA to continual work with processing of spinach in 1945-55. However, a great deal of the data and reports available refer to studies on yield at various stages of vegetable preparation. The records are incomplete in terms of reports filed with the data and vice versa. It also is not possible to locate the reasons for an increase in processing times for spinach in pints, quarts and No. 2 cans which appeared in 1957 (USDA, 1957a).

  The home canning schedules present concerns when compared to commercial processes in Bulletin 26-L (NFPA, 1982). Distinctions are made by NFPA for cut or whole leaf greens, and fill weights or initial temperatures change the schedules from two to fifteen minutes or more. Whereas the home canning schedule for pints compares favorably for whole spinach in similar cans, the schedules for quarts and cut spinach would be very inadequate.

  C. Sweet Potatoes

  It has already been mentioned that no explanation was located for a decrease in the process time for No. 2 cans of wet sweet potatoes in 1947 (USDA, 1947b). It also is apparent that the adequacy of the F0 value for sweet potatoes was questioned later (USDA, 1948b). According to the final report of this research (Reynolds et al, 1952), the F0 value for P.A. No. 3679 in sweet potatoes media was 5.8. The original process was calculated on an F0 of 5.0 (Toepfer et al, 1946). Other results of this research show F0 values for P.A. No. 3679 equal to or less than the F0 value used in process determination. The F0 = 5.8 was determined on sweet potato juice extract, however, and the difference in sugar content between this and the canned vegetable product were offered as reasons for more research (USDA, 1948b). No references to further study of this point were located, and the processing times for canned sweet potatoes were never changed.

  In NFPA Bulletin 26-L, there is a significant difference in process schedules for solic (dry) pack sweet potatoes and syrup (wet) pack sweet potatoes. The literature on heat penetration suggests that there should be this difference, but the home canning schedules show only 10 minutes additional for pint jars of the dry pack. The difference for quarts amounts to 5 minutes. A comparison with Bulletin 26-L suggests that the dry pack schedule for home canning of sweet potatoes could be inadequate.

  D. Other Low-Acid Vegetables

  Several other processing times for hot-packed vegetables appear to have been changed to coincide with raw-packed determinations. Explanations for this philosophy can be found in a report of the research by Cover et al (1956). However, there is no definite reference in USDA file reports to this being the basis for changes in 1957 (USDA, 1957a). Also, the raw-pack recommendations for cream-style corn, whole kernel corn, peas and summer squash were rounded off below the process calculated from the data (Cover et al, 1956; USDA, 1957a). Often, the literature reports and data which are available for products in USDA recommendations do not contain information for all four types of containers found in processing timetables. Therefore, the procedure by which these recommended processing times was derived is unclear.

  Another interesting issue studied by Zottola et al (1978) was the safety of canned strained (pureed) squash or pumpkin using current recommendations. Diverse product viscosities from the same recipe yielded a wide range of F0 values. The authors recommended canning cubed pumpkin or squash only since heat penetration data for this product were more uniform than for strained. This issue perhaps requires a decision on a standardized policy regarding recommendation for canning strained pumpkin.

  No adequate data to support the home-canning process schedules for mushrooms were located. An annual report from USDA (1948a) indicates that mushrooms were used in bacteriological studies with P.A. No. 3679. An F0 value of 6.0 was indicated and, after preliminary heat penetration studies, half-pint jars of mushrooms inoculated with 5000 spores of P.A. No. 3679 were processed. Spoilage occurred after a 20-minute process (F0 = 4.68) but not after a 30-minute process (F0 = 6.4). Processing studies were to be continued, and no data could be located for this or later studies. Commercial processes for mushrooms have increased three times in the last twelve years, and stringent controls on packing styles and methods exist for this vegetable. The need for research on home-canned mushrooms is indicated.

  E. Meats and Poultry

  As described earlier, no data are available for the process recommendations for ground meat, sausage, corned beef, heart and tongue, soup stock, giblets and rabbit.

  F. Acid Fruits

  The origins of the current process recommendations for fruits and tomatoes can be traced to a specific research project. However, reports of the data are incomplete in file literature and apparently nonexistent in the published literature. The file reports available do not delineate very well between preliminary data, final data, and data illustrating calculations upon which decisions were evidently made. There is an indication in these reports that some heat-resistant fruit milks exceeded process times which were subsequently recommended for those products.

  In 1947 (USDA, 1947b), recommendations for fruit juices and fruit purees offered processing times at 180F. By 1957 (USDA, 1957a), these schedules had changed to 212F processes. The explanation or discussion of issues concerning this change could not be referenced.

  Fungi belonging to the genus Byssochlamys, B. fulva in particular, have been implicated as an important factor in a variety of canned fruits. B. fulva has received much attention in recent years and has become recognized as a test organism for calculating schedules, due to its unusually high heat resistance. Lopez (1981) states the heat resistance as 30 minutes at 190F or 16 minutes at 212F. Hatcher et al (1979) studied the thermal resistance of three B. fulva strains and demonstrated Z-values of 7, 9.5 and 14F. These low Z-values indicate the need for critical control of processing temperatures, as slight fluctuations result in large time differences. The concern with spoilage by B. fulva has not been applied to home canning recommendations for fruits.

  G. Tomatoes

  Tomatoes deserve special consideration because of a controversial history regarding recommended process times. The process times for whole tomatoes were the same in 1947 and 1957 editions of HG-8. However, the process times for tomato juice in pints and quarts were reduced five minutes in the 1957 edition.

  Early heat penetration, quality and bacteriology studies carried out with tomatoes were reported in quarterly progress reports in 1944 (USDA, 1944b, Apr. - June; 1944b, July - Sep.). These studies were apparently carried out in the labs at Beltsville. Reference prior to these reports indicate that surveys had been made to document causes of spoilage in home-canned tomato products (USDA, 1943b; 1944b, Jan. - Mar.).

  Reports from 1944 indicate that a Z = 17 value was adopted, as it represented the slope of a thermal death time curve for butyric anaerobes. Early inoculated-pack studies (USDA, 1944b, July - Sept.) showed no spoilage with a 45-minute process for an average of F212 = 2.7. Correlation of heat penetration data and F0 values indicated that approximately 195F was the desired maximum center temperature to reach in processing. This appeared to require 45 minutes, also, although the maximum temperature attained in 50 minutes was only 196F with F 212 = 2.8.

  A later report (USDA, 1944b, Oct. - Dec.) of cold-packed (sic) quarts processed for 45 minutes shows spoilage in both control and inoculated packs. No spoilage was found with a 50-minute process. Finally, in an annual report from USDA files (USDA, 1945a), process determinations for home-canned tomatoes were described. A portion of that report (p. 4-5) is reproduced below, as it appears to be the last reference to process studies of tomatoes in the literature.

  "Preparation of tomatoes for canning consisted of sorting and trimming to remove, bruised and decayed tomatoes, blanching for ¼ to 1½ minutes in boiling water depending upon size and ripeness, cooling in water, skinning and coring. Some were left whole and some quartered for comparing the two types of pack.

  "Packs of tomatoes were varied to include whole, quartered, hot and cold packs. Raw packs were used for the nutritive value and inoculated pack studies. All jars were filled to one inch head space.

  "Process determination for the home canning of tomatoes included determination of heating-cooling curves, process calculations, and inoculated pack checks. Heat penetration data were obtained with cold packed, quartered tomatoes packed in quart self-seal jars and processed in the boiling water bath for varying periods of time. It was found that the center temperature of the jars continued to rise for a period after their removal from the water bath. Since this rise was unpredictable and added considerably to the sterilizing value of the processes it was necessary to establish heating-cooling curves for each period. process calculations ere based on the thermal death time of a butyric anaerobe isolated from spoiled tomatoes with an adopted value of 17 for the slope of 3minutes at 212F. This procedure yielded some margin of safety by allowing for a greater heat resistance than that of the isolated organisms. On this basis, 30, 40, 45, and 50minutes water bath processes of quartered, cold-pack tomatoes in quart jars had F0 values of 0.64, 1.1, 2.7, and 2.8, respectively.

  "Heat penetration data were also obtained with precooked, quartered tomatoes hot packed in quart jars processed in the boiling water bath for varying periods of time. The precook temperature was found to be sufficient in sterilizing value to destroy the butyric anaerobes described above. The length of process having a sterilizing value sufficient to destroy the small inoculum of butyric anaerobes which may be obtained during the filling of the jars was found to depend on the initial temperature of the pack as follows:

  175 F initial temperature, process time 30 minutes
  180 F initial temperature, process time 20 minutes
  185 F initial temperature, process time 10 minutes
  190 F initial temperature, process time 0 minutes

  "Inoculated packs of quartered, cold packed tomatoes in quart jars were prepared for checking calculated processes. Jars were inoculated at the center with 1 ml of suspension containing 100,000 spores of the isolated butyric anaerobe GHN and HE #32-12a-14 processed in the boiling water bath for periods of 30, 40, 45, and 50 minutes, and observed during incubation of 37C for periods of two months. Following incubation, jars were opened and checked for survival of butyric anaerobes by subculturing into suitable media. The results indicated 100 percent survival of the organism after a 30 minute process, 35 and 14 percent survival, respectively, following 40 and 45 minute processes and sterility after 50 minutes.

  "Nutritive value studies of tomatoes in relation to canning were limited to investigations of changes in ascorbic acid content. When ascorbic acid determinations were made on canned tomatoes subjected to different processes no consistent relations between sterilizing value of the processes and ascorbic acid retention were observed. There were some indications that ascorbic acid loss was related to mechanical loss of liquid during processing. Overall loss of ascorbic acid in processing was, however, low. With two batches of tomatoes packed in quart jars and processed for 42 minutes, 93 to 94 percent of the original ascorbic acid was present after processing. Storage at room temperature for 6 months resulted in additional losses of 13 to 25 percent."

  Although it seems that these results were accepted as the final data, the process recommendations released consisted of a 45-minute process for quarts of tomatoes (USDA, 1947b). The only other data available on process origins for home-canned tomatoes are from the Massachusetts Agricultural Experiment Station. These data are from heat penetration tests, but no conclusions accompany them.

  The only subsequent reference to USDA research with tomatoes was found in the annual progress report of the next year (USDA, 1946a). Evidently surveys had been made to determine the adequacy of home canning procedures. These surveys indicated that spoilage of acid products was much more extensive than was expected, especially for tomatoes. Research was undertaken to obtain adequate data on the thermal death times of acid food spoilage organisms. This information was to be combined with heat penetration data to compute new home canning recommendations. Once again, the summary interpretation of results is unavailable.

  The literature contains numerous references to research on spoilage of canned tomatoes. B. thermoacidurans, later labeled B. coagulans, was identified by Berry (1933) and implicated as a cause of spoilage in canned tomato juice. Anderson et al (1949) found that increasing salt concentrations in tomato juice from 1 to 8 percent lowered the pH of the tomato juices and resulted in more rapid thermal death rates. Increasing sugar concentrations from 10 to 50 percent increased the thermal resistance of this organism. At constant pH levels, the addition of acetic acid was more effective in decreasing heat resistance than other organic acids. Rice and Pederson (1954a; 1954b) also looked at the effects of pH and organic acids on the growth of B. coagulans in canned tomato juice and are credited with the conclusion that growth of B. coagulans is inhibited at pH 4.3 or lower.

  In the mid-1950s, the acidity level of tomatoes became a real concern as related to processing recommendations. Large-scale surveys were undertaken to determine pH values for tomatoes. Evidence reviewed by Powers (1976) indicated that the pH of some tomatoes was well above 4.5. Powers (1976) provides an excellent history of petitions for amending the standard of identity for canned tomatoes to allow for acidulants.

  In the early 1970s, home canning processes for tomatoes were analyzed because of outbreaks of botulism due to these products. In 1974, a meeting of scientists from the CDC, NCA, FDA and USDA issued the recommendation that home canners should add citric acid, that they should hot pack tomatoes and that they process to achieve a center temperature of 190 F for at least two minutes (Powers, 1976). The level of citric acid to be added was vague (the tomatoes should "have a definite acid taste"). Since 1974 a wide variety of recommendations for increased process times or added acidulants has occurred.

  The reader is referred again to Powers (1976) for a more complete review of the literature on acidification of canned tomatoes than is possible here. However, a few articles of particular interest will be summarized. The Eastern Regional Research Center, ARS, USDA, began collections of data on the pH of tomatoes in 1975 (Sapers et al, 1978). Ripeness, decay and bruising result in elevated pH values above a safe level, but cultivar alone was found to offer a minimal risk (Sapers et al, 1978). Therefore, home canners were advised not to be too concerned by tomato varieties, but rather to select only top quality tomatoes and to use recommended processes. Studies on acidulants continue to offer new alternatives (Maruyama and Fox, 1977; Savani and Harris, 1978; Skelton and Craig, 1978; Skelton and Marr, 1978; Zimmerman et al, 1978).

  In 1976 Huhtanen et al (1976) reported that tomato juice could develop pH gradients when mold mats were present and that growth of C. botulinum was allowed in association with the mold. Odlaug and Pflug (1979) reported similar results. Mundt (1978) subsequently reported that 58 species of 21 genera of milks grown on tomato juice raised the pH from 4.1 to 4.9 - 9.0 in 35 days. Concern had thus been raised about the safety of home-canned tomato products being consumed after mold was scraped off.

  The most recent development concerning home-canned tomatoes is the possibility of spores of B. licheniformis surviving the USDA raw-pack process for tomatoes. B. licheniformis, a facultative anaerobe, was found in a high number (30%) of home-canned tomato samples (Fields et al, 1977). Strains of the spores isolated in these samples were examined for thermal resistance an pH-elevating characteristics (Montville and Sapers, 1981). It was determined that the B. licheniformis spores could survive the recommended USDA raw-pack process for tomatoes, and elevate the pH to greater than 5.2 under aerobic but not anaerobic conditions.

  The metabolic effect of B. licheniformis on C. botulinum was reported by Montville (1982). Surviving spores in jars of tomatoes processed by home-canning procedures germinated, multiplied and developed pH gradients when seals were broken. No growth or pH elevation was observed in jars with sound seals. The aerobic conditions needed for growth of the organism would thus only be a problem in jars with poor or no vacuums (indicating perhaps faulty processing). Although growth of C. botulinum toxin was not detected, there was a clostridial odor in one jar. Observations of metabiosis by others (Huhtanen et al, 1976; Odlaug and Pflug, 1978) make the possibility a matter of concern.

  Another point made by Montville (1982) was that the survival of B. licheniformis seemed to be related to canner size. No viable spores were isolated from tomatoes processed in a 15-inch diameter boiling water canner. Survival did occur with a 12-inch diameter canner, however. Heat penetration profiles indicated lethalities of 2.70 for the small canner and 7.40 for the large canner. The longer come-up time associated with using the large canner apparently increased the time at a lethal temperature. Montville (1982) recommended an addition of 10 minutes to the process time for raw-pack canning of pint jars of tomatoes.

  Hayes (1980), under contract with USDA, recently proposed an increase in processing times for raw- and hot-pack tomatoes, tomato juice, stewed tomatoes, tomato sauce and tomato sauce with vegetables. The F0 values for these products were based on the destruction of B. coagulans and the target processes were determined at levels including Z-values of 16, 18 and 20 for F0 values of 0.06 and 0.08 minutes. The final recommendations were as follows (Hayes, 1980, p. 1-4):

  Table 15
  Suggested Revisions for Canning Tomato Products

  Product	Jar Size	Process Time (Minutes)
  		210F	239F
  Cold Pack Fresh tomatoes	. pt qt	. 55 70	. - -
  Hot Pack Tomato juice	. pt qt	. 35 45	. 17 22
  Fresh tomatoes	pt qt	40 50	22 28
  Stewed tomatoes	pt qt	45 55	25 32
  Tomato sauce	pt qt	55 65	30 36
  Tomato sauce w/veg.	pt qt	55 65	32 38

  It is apparent that further study of process times for canned tomato products is required. This conclusion is justified in light of the nebulous history of the process determination and recent research on metabiosis in this product. The recent developments on metabiosis in borderline acid food products also indicates the need for research with the levels of acidification necessary for the specialty packs which have continually increased in popularity with home canners. Mixtures of acid-low acid food products, acidified specialty products and foods with pH values which are borderline to pH = 4.6 deserve attention. Some of the concerns with these products are delineated in the following section.

  H. Acid-Low Acid Mixtures; Acidified Products

  The use of acids in canning was not generally considered until work on home canning was published by Cruess in 1914 (Fong, 1926). He found that brine acidified with lemon juice and vinegar reduced the thermal resistance of spoilage organisms in canned vegetables. Fong (1926) and Cruess et al (1925) presented data for changes in pH during exhausting and processing of vegetables in acidified brines. The pH values of acidified brines increased greatly during exhausting and to a lesser extent during processing; neutral brines of pH 7.0 decreased in pH.

  The final pH value of the canned product was more important than the original pH of the brine in decreasing thermal resistance of spore-forming bacteria. A pH value of 2.8 was required to prevent C. botulinum spoilage (Fong, 1926). Bigelow and Esty (1920), Weiss (1921a; 1921b), Dickson et al (1922), and Esty and Meyer (1922) also reported a direct relationship between a pH value and thermal resistance of C. botulinum. It is now accepted that pathogenic bacteria, including C. botulinum, are inhibited by pH 4.6 or lower (Townsend et al, 1956; IFT, 1977). Acid foods, pH < 4.6, may be canned in boiling water while low-acid foods, pH > 4.6, must be processed under pressure (IFT, 1977). Acids exert a germicidal effect because high hydrogen ion concentrations can denature microbial cell proteins. Most researchers also agree that pH determines the degree of ionization of inhibitors in food systems. It is the equilibrium pH of the food system which determines the choice of canning method. The equilibrium pH is affected partly by the buffering capacity of food and the ratio of product weight to acid volume. These and other factors critical to equilibrium pH need to be studied. (Johnston, et al, 1977).

  The best recommendations for mixtures of acid and low-acid foods to data have recommended that combinations be canned by a process appropriate to the highest pH ingredient in the product or the ingredient having the longest process time. Yet a USDA survey (Davis and Page, 1979) and other surveys indicate that 20 percent of home canners make products with combinations of acid and low-acid ingredients and use inappropriate methods for processing. However, there is at present no accepted method to determine the equilibrium pH of a combination product without controlled research for each formulation.

  Recent work at the Eastern Regional Research Center (Sapers et al, 1981) has examined the problem of identifying guidelines for safe home canning of acid-low acid combination products. A recipe data bank and method of data processing were developed to classify tomato-based combination products according to pH. It is suggested that this classification system and allied methods of pH prediction based on a series of calculations can be used to determine appropriate canning methods. This method of pH prediction has not yet been proven by the test of time and a few precautions seem necessary. The calculations will perhaps be recognized as helpful in screening certain recipes, but the adequacy of specific processes (time and pressure) would still have to be verified experimentally. Products which overlap pH 4.6 must be considered as low-acid.

  The need for further research with combination products was illustrated in the past year with confusion over recommendations for a zucchini-pineapple juice product. Several formulations for this product were abundant throughout the country. Some recipes proved to be successful and others resulted in spoilage. It was determined through a few quick research projects that some recipes did not have a satisfactory ratio of acid to low-acid ingredients. Studies at Purdue (Howe et al, 1982) and Penn State (Kuhn and Andress, 1981) arrived at conflicting process times, and USDA (Baldauf, 1982) eventually compiled the data and issued a recommendation. However, for reasons of insufficient funding, neither study was conducted with the classical methodology necessary for determining thermal process schedules.

  I. Peppers and Figs

  As denoted in Table 2, home-canned peppers were responsible for a larger number of outbreaks of botulism from 1970-79 than any other food category (CDC, 1979). The control of pH of peppers may be a critical factor affecting the safety of these home-canned products. The pH of peppers is high enough to permit the outgrowth of C. botulinum spores which survive processing.

  A large number of recipes for canning peppers require acidification or pickling; however, the levels of acidification and use of appropriate thermal processes have been subjected to scrutiny by Sapers et al (1980) at the USDA Eastern Regional Research Center. After an analysis of recipes for home-canned pepper products, they revealed inconsistencies between acidification levels and thermal processing methods. Subsequent research was conducted to determine acidification requirements for home-canned peppers. The addition of 1 tablespoon of vinegar (5% acidity) per pint jar of peppers was suggested to reduce the product pH to 4.6 or below. Varietal differences in pepper acidity and buffering capacity were also studied, and the acidification requirement was based on the more highly buffered cultivars.

  The process recommendation for these peppers was suggested to be that designed for the nonacidified low-acid product, as an extra safety precaution against botulism outgrowth. This may be an overkill and may discourage its use. Often when acidification is used to adjust pH and not to produce a pickled product, citric acid or lemon juice is the choice acidulant. An equivalent amount of bottled lemon juice may be preferable to vinegar for acidifying peppers for home canning in order to produce a "cleaner" flavor, in the opinion of these authors.

  Due to the fact that these data are relatively new it still remains to be seen whether they will affect the safety of home-canned pepper products. The length of time required for incorporation of this practice by home canners must be a concern. Further studies and replications of the data would also seem desirable. Peppers are also a major ingredient in many specialty products which home canners are demanding and preserving. Data from analysis of these recipes for the ratio of acid to low-acid ingredients, equilibrium pHs and thermal process requirements are not available in the published literature. The use of peppers in home-canned combination products, therefore, presents an area for concern and needed research.

  Home-canned figs have also been implicated in outbreaks of botulism. As cited by Ito et al (1978), Meyer and Eddie cited 12 outbreaks in the U.S. and Canada as of 1965. Figs, like peppers, are a product which lose their character with a severe process. Therefore, the home canner may be reluctant to give them the necessary process. Commercial processes consider acidification of figs as an acceptable procedure.

  Ito et al (1978) studied the inhibitory effects of pH on the growth of C. botulinum spores in figs packed in various styles of syrup. Sugar syrup concentration did not appear to affect outgrowth of C. botulinum spores. Maintenance of pH 4.9 or less prevented the outgrowth of spores. The figs in these studies received a commercial process, however.

  Woodburn (1982) has studied the pH of Oregon-grown figs, prior to and after cooking, and acidification of figs required for boiling-water canning. The average pH of fresh figs was 5.51, and an increase in pH occurred with progressive ripening or mold growth. Varietal differences were indicated for those studied. Woodburn recommended acidification with one metric tablespoon (15 ml) of 4 percent lemon juice per pint of figs before covering with syrup and processing.

  The limited number of studies and data leave a need for further research on acidification levels, ingredient ratios and thermal process determination using home processing methods. A review of Extension Service publications revealed discrepancies between acidification ratios and processing instructions for home-canned figs. In at least one case, figs were classified as an acid food product. Perhaps a more complete analysis of recipes for canned figs is required along with determination of their safety through research.