3.2.5.c Vinification tank filling process

Transferring the harvest into the vats

Several possibilities are available depending on the wine type, vatting speed and the desired level of berry integrity. One possibility is to pump the grapes from the destemmer/crusher output to the top of the tank being filled. A second possibility is to fill tanks by gravity using a mobile harvest vat that is moved directly to the opening at the top of the vat to tip in the grapes.

Optimal filling volume

The volume of a batch in hectolitres should be slightly lower than the theoretical container capacity. If the two volumes are the same, the tank will be filled to 100% of its capacity, which can lead to fermentation overflow due to the yeast's CO2 production. The volume of CO2 released during fermentation is considerable, about 50L per litre of fermented must. Other factors such as the protein content of the nitrogenous constituents of the grapes, the nature of the yeast strain and the fermentation temperature can influence the yeast's CO2 production.

For this reason, a filling percentage should be deducted for each vat of a different volume in order to determine the maximum filling volume of a vat to avoid overflowing. Generally, 20% of the volume of a vat is deducted, which means that a 150 hL tank can contain 120 hL of grapes. The ideal volume is 80% of the container's theoretical capacity.

Temperature management during filling

Heating or cooling the harvest once it is in the vat is a possibility. When a cold pre-fermentation maceration is envisaged in order to improve the wine's aromatic profile, the harvest should be cooled. An ideal temperature is between 5°C and 10°C. On the other hand, when a rapid onset of fermentation is desired, in order to reduce the development of micro-organisms and deviations, heating the harvest facilitates a rapid start to fermentation.

Heating and cooling are carried out using thermo-regulated tanks or by using mobile cooling curtains. Nevertheless, the temperature is a key element during the vinification process and it is vital to avoid exceeding certain temperatures to ensure optimal fermentation quality. Above 30°C, environmental conditions become increasingly difficult for the yeasts, which can cause fermentation to stop prematurely.

Inerting tanks following vatting

It is possible to inert a container to protect the must from oxidation. The gases used include carbon dioxide, nitrogen and argon. The latter is not widely used because of its solubility in wine and its high cost. Nitrogen is the most commonly used gas and is sometimes preferred in a mixture with carbon dioxide (for example 85% nitrogen and 15% carbon dioxide). The CO2 produced during alcoholic fermentation can also be used to inert other vats.