Home Critical Review of Home Preservation Literature and Current Research
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III. Origins and Assessment of Current USDA Recommendations
BHNHE and Related Research

Chapter III Tables
Contents

Tables
Process Values for Meat and Poultry in Different Countries
Spoilage of Vegetables Inoculated With 10,000 Spores of Putrfactive
Anaerobe No. 3679 per Pint and of Controls, After Processing in Pint jars at
240° F and Incubating at 86°
Regression Equation and Standard Error of Estimate of Regression of
Process Value on Process Time; Calculated and Recommended Process
Times for Vegetables in Various Containers Processed at 240°
Lethality of Cooling Period
Origins of Home Canning Processes for Low-Acid Vegetables
Comparison of Calculated and Published Processes for Vegetables
Origins of Home Canning Processes for Meats and Poultry
Origins of Home Canning Processes for Acid Foods
Suggested Revisions for Canning Tomato Products

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):

Table 7
Process Values for Meat and Poultry in Different Containers

  Process time at 240F
Containers
  Process values
Product Minutes Kind Number Mean F Standard Deviation

Beef 90 Quart jars 8 12.6 2.9

Chicken 90
75
-----do-----
-----do-----
11
11
21.3
17.2
4.1
4.1

Chicken,
boned
90
70
-----do-----
Pint jars
8
12
17.7
11.8
3.6
1.5

Pork 90
70
90
Quart jars
No. 2 cans
No. 3 cans
73
12
12
15.0
18.3
16.2
3.8
3.7
2.1

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).

Table 8
Spoilage of vegetables inoculated with 10,000 spores of putrefactive anaerobe No. 3679 per pint and of controls, after processing in pint jars at 240F and incubating at 86F.

Product Process time at 240F (minutes) Process Values Incubation at 86F (Days) Control Jars
Number of Estimations Mean Value (F) Standard Error Total (Number) Spoiled (Number)

Asparagus 7
14
30
7
8
12
2.27
4.18
9.32
.28
.36
.23
100
100
100
12
12
12
0
0
0

Beans, lima 7
15
25
12
8
12
3.7
5.8
9.3
.17
.27
.19
120
125
175
12
12
12
0
0
0

Beans, snap

7
13
20
8
8
12
1.74
3.91
7.14
.29
.54
.31
12
135
135
12
12
12
0
0
0

Beets 5
10
15
8
9
11
2.1
2.7
5.4
.16
.27
.23
120
120
180
12
12
12
0
0
0

Carrots 6
9
15
8
8
9
2.06
3.04
5.46
.36
.32
.32
90
110
125
12
12
12
0
0
0

Corn, cream-style 70
80
9
11
12.8
15.9
.77
.32
118
155
12
12
0
0

Corn, whole-grain 20
30
40
50
9
9
12
9
5.5
7.8
10.9
15.0
.31
.44
.41
.41
131
164
164
122
12
12
12
12
0
0
0
0

Okra, sliced 5
10
20
9
12
9
2.3
3.5
6.5
.13
.28
.27
118
117
166
12
12
12
0
0
0

Okra, whole 5
10
9
12
2.5
3.2
.14
.34
120
121
12
10
0
0

Peas 15
25
30
8
8
9
7.3
7.5
8.5
.18
.41
.27
159
125
130
14
12
12
0
0
0

Pumpkin, cubed 20
30
50
9
8
12
3.0
4.6
8.6
.49
.52
.47
89
86
96
12
12
12
0
0
0

Pumpkin, mashed 30
40
60
9
6
10
3.3
3.6
8.0
.53
.11
.42
81
80
90
12
11
12
0
0
0

Spinach 25
30
35
38
13
8
7
8
2.15
2.46
4.41
5.03
.16
.15
.30
.31
135
110
95
150
15
12
12
12
0
0
0
0

Squash, summer 10
15
20
8
9
11
2.2
3.5
5.6
.29
.47
.34
157
118
167
12
23
12
1
0
0

Sweet potatoes, dry pack 30
40
60
90
9
8
8
11
3.4
4.9
9.1
18.1
.39
.29
.54
.45
123
120
120
131
12
12
12
12
0
0
0
0

Sweet potatoes, wet pack 25
35
45
9
9
12
2.4
4.4
5.7
.43
.18
.28
130
136
141
12
12
12
0
0
0

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.
B. Scientifically-Determined Canning Processes Released

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.

Table 11
Origins of Home Canning Processes for Low-Acid Vegetables

Product Recommended Process Time (minutes) at 240F

1947
AIS-64 (1)
1947
HG-8
1957
HG-8 (2)

ASPARAGUS
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
25
55
20
20

.
.

-
-
-
-

.
25
40 (a)
20
20

.
.

25 (a)
30 (a)
20 (a)
20 (a)

.
25
30 (a)
20
20


BEANS, DRY W/SAUCE
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-
.
.

-
-
-
-
.
.

65 (b)
75 (b)
65 (b)
75 (b)

BEANS, DRY BAKED
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-
.
.

-
-
-
-
.
.

80 (b)
100 (b)
95 (b)
115 (b)

BEANS, FRESH LIMA
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
35
60
40
40

.
.

-
-
-
-

.
35
60
40
40

.
.

40 (c)
50 (c)
40
40

.
40 (c)
50 (c)
40
40


BEANS, SNAP
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
20
25
25
30

.
.

-
-
-
-

.
20
25
25
30

.
.

20 (d)
25 (d)
25
30

.
20
25
25
30


BEETS
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

25
55
30
30
.
.

25
45 (a)
30
30
.
.

30 (a)
35 (a)
30
30

CARROTS
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
20
25
20
25

.
.

-
-
-
-

.
20
25
20
25

.
.

25 (c)
30 (c)
25
30

.
25 (c)
30 (c)
20
25


CORN, CREAM STYLE
Raw Pack
PT
2 CAN

Hot Pack

PT
2 CAN
.
.

-
-

.
85
105

.
.

-
-

.
85
105

.
.

95 (c)
105
.
.
.
85
105

CORN, WHOLE
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
55
85
60
60

.
.

-
-
-
-

.
55
85
60
60

.
.

55 (c)
85 (c)
60
60

.
55
85
60
60


HOMINY
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-
.
.

-
-
-
-
.
.

60 (b)
70 (b)
60 (b)
70 (b)

MUSHROOMS
Hot Pack
½ PT
PT
2 CAN
.
.

-
-
-
.
.

-
-
-
.
.

30 (a)
30 (a)
30 (a)

OKRA
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

25
40
25
35
.
.

25
40
25
35
.
.

25
40
25
35

PEAS, FRESH
BLACKEYE

Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.
.

-
-
-
-

.
-
-
-
-

.
.
.

-
-
-
-

.
-
-
-
-

.
.
.

35 (e)
40 (e)
35 (e)
40 (e)

.
35 (e)
40 (e)
30 (e)
35 (e)


PEAS, FRESH GREEN
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
40
40
30
30

.
.

-
-
-
-

.
40
40
30
30

.
.

40 (c)
40 (c)
30
35

.
40
40
30
35 (c)


POTATOES, CUBED
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-
.
.

-
-
-
-
.
.

35 (b)
40 (b)
35 (b)
40 (b)

POTATOES, WHOLE
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-
.
.

-
-
-
-
.
.

30 (b)
40 (b)
35 (b)
40 (b)

PUMPKIN, CUBED
& WINTER SQUASH

Hot Pack
PT
QT
2 CAN
2½ CAN
.
.
.

55
90
50
75
.
.
.

55
90
50
75
.
.
.

55
90
50
75

PUMPKIN, STRAINED
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

60
80
75
90
.
.

60
80
75
90
.
.

65 (a)
80
75
90

SPINACH & GREENS
Hot Pack
PT
QT
2 CAN
2½ CAN
.
.

45
70
60
75
.
.

45
70
60
75
.
.

70 (a)
90 (a)
65
75

SQUASH, SUMMER
Raw Pack
PT
QT
2 CAN
2½ CAN

Hot Pack

PT
QT
2 CAN
2½ CAN
.
.

-
-
-
-

.
30
40
20
20

.
.

-
-
-
-

.
30
40
20
20

.
.

25 (c)
30 (c)
20
20

.
30
40
20
20


SWEET POTATOES,
DRY PACK

Hot Pack
PT
QT
2 CAN
2½ CAN
.
.
.

65
95
80
95
.
.
.

65
95
80
95
.
.
.

65
95
80
95

SWEET POTATOES,
WET PACK

Hot Pack
PT
QT
2 CAN
2½ CAN
.
.
.

55
90
70 (a)
90
.
.
.

55
90
70
90
.
.
.

55
90
70
90

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).
Origins of Changes