Mathematical calculation of the effectiveness of canned sterilization regimes
It was noted above that in the factory, during the sterilization process, they are guided by the so-called sterilization formula, which indicates the sterilization temperature and the duration of the individual stages of heat treatment. Technological instructions for the production of canned food always contain appropriate sterilization formulas for this type of canned food.
However, one should not think that these formulas are once and for all established dogma, not subject to verification or change. In some cases, there is a need for changes, for example, the sterilization temperature, say, increase from 120 to 130 ° C, or, conversely, lower from 100 to 85 ° C. Then the formula needs to be changed or developed a new kind of canned food, for which the instruction does not yet have a ready-made formula. And sometimes a new type of tare will appear, which also does not have a corresponding sterilization formula.It is also possible that it is necessary to check the current sterilization formula when there are doubts about its effectiveness (for example, the appearance of an increased preservation marriage during storage), etc.
In short, you need to be able to verify the effectiveness of certain sterilization formulas, as well as be able to develop new modes for different conditions.
It would seem that there should be no particular problem in such a check. In fact, in each particular case, it is necessary to select the values of only one process parameter — time, because the sterilization temperature should be set in advance, guided by the chemical composition of the product. Therefore, choosing the process temperature in advance, you should only look at the appropriate table and find the appropriate heat treatment time at this temperature.
However, the reality is much more complicated. This could have been done if, when the cans were immersed in the sterilization apparatus, the desired sterilization temperature occurred instantaneously in the whole mass of the product. However, the temperature in the apparatus increases, and in the product gradually, in increasing order, and when cooled, it also gradually decreases.Thus, in the sterilization process there are many temperatures, the lethal effect of which differs significantly from each other in time.
Therefore, the universally accepted and legalized principle of checking and calculating the required sterilization time consists in dividing the entire heat treatment process in the sterilization apparatus into individual small time intervals and measuring the temperature corresponding to each such segment, recalculate the time of each segment to the equivalent action of some kind one particular temperature, chosen as the standard for comparing with it the action of all other given temperatures. Then, summing up the results of such a recalculation of the time of action at different temperatures for the equivalent of the effect on microorganisms of one of some predetermined predetermined reference temperature, we obtain the total estimate of this mode, expressed by the time of action of one temperature. This time is conditional, because it corresponds to an imaginary process in which canned foods, immersed in a sterilization apparatus, are instantly heated to the reference temperature, kept the number of minutes found and instantly cooled.But this imaginary process produces the same effect on microorganisms as our real process, in which the temperature of the product gradually rises and gradually cools.
Such a recalculation is convenient in that the whole variety of variables of the sterilization process — temperature and time — is expressed by one number. This number — time at a constant reference temperature — is called the lethality, or sterilizing effect, of the process.
As a reference temperature, as applied to sterilization regimes, 121.1 ° C is most often taken (this “non-circular” number is obtained when converting 250 ° Fahrenheit, adopted in the United States, to centigrade Celsius scale), and in relation to canned acid - 80 ° FROM.
The calculation of the actual lethality of this mode of sterilization is carried out according to the formulas for low-acid canned food.
The experiment was carried out in such a way that during the sterilization process, temperature measurements in the apparatus and in the depth of the product were taken every 5 minutes. The measurement results were recorded in Table. 3. At the end of the experiment, the values of the coefficients were entered in the appropriate column against each product temperature.Table of values is in a number of textbooks.
In accordance with all the values of the coefficient must be summed up and the resulting amount multiplied by 5 (in this case = 5 min). Sum = 0,51, and the desired value of mortality services. min 70
The result obtained should be understood as follows: heat treatment carried out for 110 minutes (25 + 60 + 25), at variable temperature conditions (now increasing, then decreasing), has the same effect on microorganisms as if the temperature in the bank was instantly raised to 121.1 ° C, kept at this temperature for 2.55 minutes and instantly lowered to non-lethal values for microbes.
So what happens can be called the decoding of the lethality of the given sterilization regime. The question of how effective this mode is, i.e., whether the found value of mortality is sufficient, or whether it is excessively large, can be solved by comparing the value of actual mortality with the normative one that guarantees the required degree of sterility. The latter are also amenable to calculation and are given in the relevant allowances.
For example, the required lethality of sterilization regimes of canned vegetables eateries is set to 1 conv. minTherefore, the resulting mode. Durable, and it can be cut.