We have previously seen that cooling has significative repercussions on the renneting behavior of milk, notably on the coagulation time (lenghtened), the firmness of the gel (reduced), and curd drainage (more difficult) (Lenoir et al., 1974). Cooling milk and keeping it at low temperature reduces its fitness for cheesemaking when compared to fresh raw milk, especially if the storage time exceedes 48 hours. Although the physical- chemical changes due to cooling are essentially reversible, they take place too slowly to let cooled milk recover the cheesemaking qualities of the original fresh milk simply in the interval of time required to heat it to the renneting temperature.
Some methods exist to accelerate this process, including addition of calcium salts, acidification, biologically ripening the milk, and increasing the protein content.
The addition of 0.2 g/L of calcium chloride to the cooled milk is generally sufficient to correct the effects of refrigeration for 48 hours at 3°-4°C. Keeping the milk at 30°-35°C for 60 minutes after calcium chloride addition improves the effectiveness of the treatment.
Standardizing the pH of the milk by addition of an organic acid solution, CO2 or by action of starter cultures is an effective method to normalize the rennet activity, and as a consequence, the coagulability of milk: The coagulation time is shorter, the gel is firmer, and the curd losses into the whey are limited (Amram et al., 1982). As a matter of fact, a number of cheesemaking methods include lactic acidification before rennet- ing. The addition of calcium chloride might also be advantageous.
Biological ripening of the milk with a small quantity (0.1%) of mesophilic lactic cultures for 15 to 16 hours at 10° to 12°C is another effective method for favoring coagulation and restoring the rheological qualities of the gel. It can be combined with the addition of calcium chloride as well.