The techniques with variable relative humidity involve more aggressive drying phases regularly interrupted by periods of resting necessary for the characteristics of the external fraction to remain unchanged; during these interruptions, in general the air circulation is stopped, and there is an increase in the environmental relative humidity by evaporation of the water from the product and a rehydration of the external fractions by diffusion of the water from the more internal fractions (Fig. 2).

Figure 2 (a) Behavior of RH in drying of Italian salami. (b) Behavior of T in drying of Italian salami.

0 100 200 300 400 S00 600 700

Figure 2 (a) Behavior of RH in drying of Italian salami. (b) Behavior of T in drying of Italian salami.

The profile of the mean relative humidity in the two techniques follows differing trends: ascending in the case of the techniques with variable relative humidity and descending in the other case. The choice of one or the other technique depends on numerous factors, which cannot be more closely examined here. It is important, however, to evaluate the influence of one technique or the other on all the characteristics of the product: internal temperature, surface microbial flora growth, and drying of the casing.

Accentuated drying facilitates a certain diminution, by as much as several degrees in the internal temperatures of the product, as a consequence of the high quantity of heat absorbed by evaporation (on day 2 of drying an Italian salami having a casing diameter = 90 mm, a lean mean/fat = 85/15, the averages of room temperature and internal temperatures were 16.08 and 14.33, respectively; personal data), the selection of the microorganisms most resistant at low Aw values and the rapid drying of the casing.

Traditionally the variable relative humidity technique was chosen for salamis with low acidification and stuffed in natural casing with poor permeability; the second technique was adopted in virtually all other situations.

The values of the main control parameters are defined in differing ways; for the techniques with constant relative humidity values, the choice is based principally on objective parameters (optimal temperature values for the type of fermentation, a preset difference between relative humidity and internal Aw, whereas for those with variable relative humidity values, the experience of the operators counts for more and is helped by the use of systems designed to improve the processes based on statistical techniques. It is not in fact easy to judge solely by means of objective parameters the moment to interrupt drying—that is, when the surface is too dry—and to begin another drying cycle when the surface is sufficiently wet.

Surface microbial flora growth control introduces a further complication to the choice of the relative humidity values: in the case of the constant relative humidity techniques, the choice of the starter cultures is fundamental (26), as is everything linked to environmental pollution. For the other technique, because the salamis are stored for a certain period at relative humidity levels lower than optimal values of the growth of undesired strains, it is possible, by acting on the drying and reequilibrium times, to improve surface microbial flora control.

D. Choice of Temperature and Relative Humidity Values in the Different Periods

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