The General Method of process evaluation is used to calculate F 160.0°F values for two ground-beef patty frying tests. The F 160.0°F value is then used to compare the adequacy of the two frying processes to control pathogenic microorganisms. The several elements of process design and evaluation are described: (1) designing the microbial control process, (2) performing the General Method of process calculation including construction of the relative kill time graph, (3) selecting the z value, (4) evaluating relative kill time, lethal rates, and F T values, and (5) calculating F 160.0°F values for two ground-beef patty frying tests as examples.

Heat penetration (HP) test data have been obtained for water in 13 sizes of metal cans and for 16 fluids with different physical properties in 211 × 400 metal cans. Data were collected until the slowest heating zone was less than 0.1 C° below the heating medium temperature. When conventional HP graphs were plotted, these natural convection heating liquids formed curves instead of straight lines. A straight line was fitted by least squares regression to the data between (T 1 - T) values from 40.0 to 4.0, 10.0 to 1.0, 4.0 to 0.4, and 1.0 to 0.2 C° and the f-values determined. The results show that the f-value of fluids that heat by convection increase with heating time, indicating that the true shape of the heat penetration data on a semilogarithmic graph is a curve.

Heat penetration (HP) test data have been obtained for water in 13 sizes of metal cans and for 16 fluids with different physical properties in 211 × 400 metal cans. Data were collected until the slowest heating zone was less than 0.1 C° below the heating medium temperature. When conventional HP graphs were plotted, these natural convection heating liquids formed curves instead of straight lines. A straight line was fitted by least squares regression to the data between (T 1 - T) values from 40.0 to 4.0, 10.0 to 1.0, 4.0 to 0.4, and 1.0 to 0.2 C° and the f-values determined. The results show that the f-value of fluids that heat by convection increase with heating time, indicating that the true shape of the heat penetration data on a semilogarithmic graph is a curve.

“Aseptic” is the shorthand name for the food production system where product moves in continuous flow through a heat-hold-cool thermal process and is then filled into a sterile package. The package is sterilized, filled, and sealed in a sterile environment. Today, both acid and low-acid homogeneous liquid foods are produced by aseptic systems; low-acid foods that contain particulates in a liquid vehicle may be produced soon. The principles for establishing a heat preservation process for low-acid foods that contain particles larger than 5 mm in diameter and are to be sterilized continuously in a heat-hold-cool system are described. Only product sterilization, which is just one part of the aseptic system, is addressed. The term “heat-hold-cool” identifies the system used to achieve microbial control of the product.

This is a review paper illustrating how the heat process F T -value for low-acid canned foods can be estimated using measured values of the numbers and resistance of the spoilage organisms and an appropriate model. Heat process F T -values are calculated using the straight-line semilogarithmic model for preservation against public health, mesophilic spore economic and thermophilic spore economic spoilage. The microbiological characteristics of each type of preservation hazard are reviewed. Several appropriate values of D T and N 0 are used in the illustration calculations of F T . The presentation is summarized graphically by placing the F T -value lines calculated using the model for preservation against public health, mesophilic spore and thermophilic spore hazards all on the same graph. This gives a visual picture of the relative magnitude of the F T -value for the different types of spoilage hazard.

In this monograph an attempt is made to put into perspective several factors that impinge on the heat process value, F T . In the heat processing of low-acid canned foods (LACF), there are three specific types of final product spoilage that concern the food microbiologist and the food manufacturer. These three areas are discussed in some detail. The order to follow in the design of LACF and endpoint values are suggested. Use of descriptive and numerical terms for the endpoint of the LACF heat preservation process is discussed. The origin of the term, “commercial sterility,” is reviewed; reasons for replacing this term (in the future) with a specification are presented. The several faces of the widely-used heat process value, F T , are examined. The use of a safety factor to take care of unknown processing conditions is proposed. Suggested safety factors are listed. The classical research of Esty and Meyer on resistance of Clostridium botulinum is reviewed and interpreted using the simple logarithmic model. The often-quoted but poorly-understood term, 12D, is discussed.

In this report a case is made for food microbiologists to define or locate the endpoint of a preservation process using a numerical specification rather than descriptive terms. Examples of numerical specifications are presented. It is recommended that the specification be on the basis of one unit where the endpoint specification is the probability of a nonsterile unit (PNSU). Procedures for experimentally establishing or verifying the preservation process necessary to produce the endpoint specification are described.

The objective of this review paper is to support the use of the semilogarithmic microbial destruction model as a tool for arriving at an appropriate heat process F T -value. Both “science” and “engineering” are important in preserving food; however, the actual heat processing of the food product is an engineering operation and requires an engineering approach. The characteristics of an engineering design model are discussed and are contrasted with the requirement of a model to fit scientific data. A case is made for the use of the simple semilogarithmic model as an engineering design model for determining the heat process F T -value. An example is presented regarding how the model can be used to understand the effect of a change in product initial microbial load on the number of observed failures.

A general relationship between a relative change in the temperature response parameter, f, and the sterilization value delivered in a thermal process has been developed. The relationship is based on numerical differentiation of Ball's formula method and employs a dimensionless elasticity term to express the relative change in sterilization value due to a relative change in heating rate. The funtion presented can be used for g's of up to 30°F and for changes of 3 to 20% in the value of the temperature response parameter.

In crateless retorts under certain conditions, it is possible for a few cans in the retort load to have an end flat against a solid wall. Cans under this condition will have a temperature response parameter, f h , larger than cans surrounded by the heating medium and a smaller sterilizing value (F o ). The f h and F o -values of cans, both with an end flat against a solid wall and surrounded by the heating medium, are calculated to show the magnitude of the effect and the possible hazard when this condition exists and is ignored. It is recommended that the possibility of a wall effect be determined as part of the prevalidation inspection, and that the heat penetration test program be based on the results of this inspection.

The objective of this study was to determine the potential for leakage of swelled cans of low-acid foods. Using a vacuum leak test, 294 (38.5%) of 764 containers tested were found to have leaks. Most leakage detected by the vacuum test was located in the canner's end area (73.5%). The lap area at the side seam-double seam junction was the specific location that had the highest incidence of leakage. Can seam measurement data indicated that insufficient seam tightness was one of the primary double seam defects. It was not possible to account for double seam leakage from the individual seam measurement data. Therefore, a scoring system was developed to give a single number that included interactions of the double seam measurements. Seam measurement scores indicated that 55% of the cans had double seams of poor or questionable quality which were judged as having a potential for leakage. The results of the vacuum leak test indicated that in 26% of the cans there was potential for leakage at points other than the double seam. Therefore, a total of 81% of the swelled cans showed a potential for leakage.

Swelled cans of low-acid food were collected from supermarkets over a 17-month period. Microorganisms were recovered from 47% of the 790 containers tested. Calculations suggested that approximately another 47% of the swelled cans were the result of microbial contamination, although no microorganisms were recovered, while 6% were physically induced (nonmicrobiological) swells. Food type appeared to influence the recovery of microorganisms. Types and incidences of organisms recovered were: 91.6% typical leaker spoilage microorganisms, 0.5% thermophiles, and 7.9% pure cultures of sporeforming organisms traditionally associated with under-processing.

Swelled cans were collected over a 17-month period from outlets of two supermarket food chains. Each swelled can was classified by product and the probable cause of the swelled condition. Using weekly sales volume data for each outlet, the incidence rate of swelled cans for each type of food was estimated. The incidence rates ranged from 2.1 to 78.4 swelled cans per 100,000 units sold, depending upon the type of food. Of the 1.104 swelled cans collected, 314 (28.4%) were found to have major container defects which were assumed to have resulted in the swelled condition. Microbiological analyses were performed on the products in the remaining 790 cans; the following results were obtained: ( a ) typical leaker spoilage, 86%; ( b ) typical underprocessing spoilage, 7%; ( c ) thermophilic spoilage, 1% and ( d ) nonmicrobial swells, 6%. Using vacuum testing and double seam measurements, the causes of the leakage were determined as follows: ( a ) poor or questionable quality canner's end double seam, 51%; ( b ) leaks at locations other than the double seam, 26% and ( c ) poor or questionable quality manufacturer's end double seam, 4%. It was concluded that examining swelled cans of low-acid foods at the retail level is a valid method for evaluating the canning operation of commercial food processing.

Three series of experiments were carried out. Each experiment consisted of six or seven tests where four or five containers were fitted with thermocouples and five were fitted with biological indicator units (BIU). The sterilization value (F 0 ) delivered to cans of peas in brine was calculated from heat penetration data. The heat penetration data were analyzed for test-to-test reproducibility within each experimental series. Sterilization values for all tests were calculated from the BIU test results. The sterilizing values F 0 (PHY) determined from physical (PHY) heat penetration data were compared with sterilizing values F 0 (BIO) determined using the BIUs, both on the basis of accuracy and variability. The mean F 0 (PHY) - F 0 (BIO) was + 1.2 min. The mean coefficient of variation of the F 0 (PHY) was 0.03 and the F (BIO) was 0.06.

The efficiency of four culture media for recovery of heat-activated and heated Clostridium sporogenes spores was studied. Yeast extract agar gave the highest spore recovery. The effect of the method of preparing the yeast extract agar on the recovery of heated spores was also evaluated. The results indicate that ( a ) a significantly lower spore recovery was obtained when the dextrose was omitted completely or when added to the medium before autoclaving, and ( b ) no significant difference in spore recovery was found between yeast extract agar freshly made or prepared and stored at 4 C up to 11 days before use.

The rate of deposition and removal of a radioactive milk soil from several surfaces have been studied. The nature of the surface exhibited a small but measurable effect on the rate of deposition of a radioactive milk soil on the surfaces tested. However, the surfaces showed no significant effect on the rate of soil removal. The build-up that took place on all surfaces due to repeated soilings without washing was not a simple additive accumulation of residue but appeared to be a selective deposit of a residue slowly laid down over a period of time and difficult to remove. As the accumulated residue increased, a point was reached beyond which there was no significant difference among surfaces in the rate of soil build-up. Subsequent washing removed only part of the soil and even repeated washings had little effect unless special heavy duty cleaning was applied.

No significant difference was found in the relative cleanability of Nos. 2B, 3, 4, and 7 stainless steel finishes as measured by bacteriological tests. Therefore, it can be concluded that from a bacteriological cleanability stand-point, based on the conditions of this study, the selection of a stainless steel finish from among those used in these studies for a farm bulk tank or any comparable piece of equipment should be based on factors other than bacteriological cleanability.