The term “cold spot” is used both for the autoclave and for packaging, but covers two different notions.
For the autoclave, the cold spot designates the position at which the temperature is lowest during the heating period.
For packaging, the cold spot designates the position at which the F0 (sterilizing value) or pasteurization value reached will be lowest (often, but not always, the geometric centre).
Case 1: the F0 (sterilizing value) or pasteurization value taken into account only concerns the points accumulated during the treatment heating period. In this case, the two notions are consistent, giving a good correlation between the cold spot of the autoclave and the position of the packaging presenting the lowest F0 (sterilizing value) or pasteurization value.
By contrast, the choice not to consider cooling results in considerable overcooking effects, especially on products with conductive behaviour.
Case 2: in accordance with the method applied in France and in most European countries, the F0 (sterilizing value) or pasteurization value is calculated on the entire treatment process, including heating and cooling periods. From this point on, the notions of autoclave cold spot and packaging cold spot are no longer equivalent. In fact, the location of the packaging with the lowest F0 may be the exact opposite of the autoclave cold spot! It all depends on the homogeneity of cooling.
To avoid any error, a heat penetration study should simply be performed instead of temperature distribution mapping. The advantage of this method is that it minimizes the effects of overcooking with conductive products. In effect, it is common to accumulate more F0 (sterilizing value) or pasteurization value points on cooling than during heating.
Note: for highly convective products, temperature distribution mapping may be sufficient, since the F0 (sterilizing value) or pasteurization value points acquired on cooling remain minimal.
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