4.1.5.c Is a cold pre-fermentation maceration necessary?

CPM (cold pre-fermentation maceration also known as cold soak) consists of keeping the grapes in the vat at a cool temperature between 5 and 12°C, usually for a period of 2 to 6 days. For this, dry ice and/or a thermoregulation system in the vat are used.
The main purpose is to obtain more aromatic precursors since the anthocyanins will develop during alcoholic fermentation, no matter what happens. It is a difficult technique to implement and is often requires a lot of energy. It is frequently used on Bordeaux's right bank and in Burgundy.

A cold soak can also help winery logistics and pressing since the start of fermentation can be delayed, and therefore its completion and the time that pressing takes place. For example, for certain profiles suited to CPM, the must can be kept chilled in the vat for 5 days, while another vat brought in the same day can be fermented immediately. This introduces a welcome gap between the operations to be carried out on the respective vats.

However, if the grapes are not sulphited or there is no biocontrol, an odour of ethyl acetate or acetic acid may develop. This phenomenon is due to the growth of yeasts such as Kloeckera apiculata. Aeration may be sufficient to eliminate the acetate, but vigilance is still required and the start of alcoholic fermentation should not be delayed.

Sulphur addition when the harvest arrives at the cellar or the use of non-Saccharomyces yeasts are potential means of carrying out a pre-fermentation cold maceration without risk. Similarly, inerting of the vat is very important during this practice.