For many, picking the grapes is the same, meeting, love between pickers, snacking and gerbaude/poêlée (often very festive meal at the end of the harvest).
Gathering the grapes is obviously essential to produce a quality wine, but very often people forget or do not know all the excitement that takes place in the cellar: Reception of the harvest, alcoholic fermentation, extraction, maceration, pumping over, punching down, anchoring, tasting, run-off, decanting, pressing, filling, malolactic fermentation.
An astronomical amount of work is then required in the cellar from the first shots of pruning shears to the second and last fermentation (malolactic); it is spread over a period ranging from 1 to 4 months. The wine will then be able to find calm in its barrel to be aged.
I will therefore try to describe and explain what is known in the wine industry as vinification. That being said, I would like to point out that every winegrower has his own vision of wine and therefore of how to make it.
After being picked, the bunches are brought to the cellar, where they will be taken care of by the cellar master and his team, we talk about receiving the harvest.
This last one must be sorted (remove rotten and unripe berries), the sorting can be manual or mechanical. Once the selection has been made, the crop must be destemmed, i.e. the berries must be separated from the stalk. The collected berries will then be crushed: the skin is delicately broken so that it releases its juice. Once all these operations have been carried out, the grapes must be brought to the vat, which may be made of wood, concrete or stainless steel. To carry out this transfer, a marc pump made up of a large worm screw pushes the grapes into their new home.
The latter, which may seem simple, is relatively complex for the cellar master, because he must control the volumes, i.e. choose a container adapted to the plot that has just been picked. Even if he can rely on the yield estimate, it remains hypothetical, a tank that is too full will be difficult to work on afterwards, the volume of grape must increasing during fermentation; a tank that is empty (half full) will be hard to protect from oxygen. The team must then be very reactive to any change of program, because, if the grape harvest reception stops, the pickers no longer have a crate in which to empty their bucket full of pretty grapes.
Once the filling of the tanks is completed, some additions can be made; sulphiting (protection), enzyming (extraction), wood chips (antioxidant and colour fixative). Juice can also be removed to increase the skin/juice ratio of the grapes to obtain more concentrated wines, the bleeding will then be used for rosé, or incorporated into another less qualitative batch.
Once the grape harvest tank is ready, the alcoholic fermentation begins, i.e. transforming the sugars into alcohol, this reaction will be orchestrated by the yeasts. The indigenous yeasts (present on the skin of the grapes) or yeasts selected by laboratories for their high fermentation potential will then be put into action. To facilitate this process, the vats are thermoregulated, so the juice will be kept at ideal temperatures for a frank and total fermentation, and according to the type of wine desired. These temperatures generally vary from 20 to 30 degrees. It is very important that fermentation is controlled and carried out correctly, as a stop of fermentation can lead to the creation of harmful volatile compounds. Indigenous yeasts present a higher risk, but many winemakers defend them because for them, they embody a closer and more natural version of the terroir.
In order to check that the process is running smoothly, a daily reading of the density of the must is carried out. This operation is performed using a mustimeter (PHOTO). Sugar being more dense than alcohol, the density decreases during the fermentation process; it varies from 1095 to 992. Monitoring is very important, because in support of juice analysis it allows us to know the oxygen, vitamin and nitrogen requirements and therefore to make additions at the right time.
The fermentation curve also makes it possible to control the exchanges between the solid parts (skin and seed with the juice), we then speak of extraction. Thus, extraction at the beginning of fermentation is preferred because it is sweet and very qualitative.
In order to extract, several techniques are possible, the overall principle being to put all the skins in contact with the juice.
During fermentation, there is a high release of CO2 ( Sugars + assimilable nitrogen ?action from yeasts -> alcohol + C02 + energy creation (heat)), so the tank looks like this:
The reassembling consists in spraying the cap with the juice, for this purpose we use a pump that is connected to the bottom of the tank to suck the juice which will then be returned via pipes at the top of the tank where a person is in charge of directing the juice through the marc (the pipe can also be connected to a mechanical sprinkler), when the juice slides through the millions of veins of the cap, there is exchange between the solid particles and the juice.
The punching down, a technique historically Burgundian, consists in pushing the hat under the juice with a pigeon or feet. It can be quite laborious. Indeed, the gas emission is such that the cap can be very hard.
Pigeage and reassembly are carried out several times a day at the beginning of the extraction, they can even be combined.
The unloading can also be used, it extracts very strongly so it is used at most once or twice for the same tank. All the juice is transferred to another tank, and then returned to the cap at high flow rate, thus breaking the entire cap, which allows for numerous solid-liquid exchanges.
At the end of fermentation the juice is composed of a large quantity of alcohol, which accentuates the extraction and especially that of undesirable compounds, the extraction will then be limited to the minimum, we simmer. The marc cap is only slightly watered (very small pumping over) daily, or even every other day, in order to renew the juice present in the marc and prevent it from stinging. At this moment, tasting is essential, when the cellar master and the oenologist consider that the material and fat have been extracted enough, it is necessary to drain the tank in order not to go too far and therefore to draw bitterness, greenness and dryness. The length of vatting varies according to the quality of the grapes and the wine desired, it generally varies from 10 to 30 days.
By run-off, we mean the separation of the juice from the marc, which is called free-run wine, it can be directly transferred into a barrel or another vat.
Once the run-off has been completed, the vatting must be removed: a member of the team must enter the tank to remove all the skins and pips that will be pressed. This step is dangerous because it takes long enough for the tank to no longer be saturated with CO2, which is fatal to humans. Moreover, once the C02 has been removed, the alcohol vapours are still there, they are relatively hot, and this operation is quite strenuous.
The pomace came out of its tank and will be pressed. Several types of presses exist, the most commonly used is the pneumatic press:
A membrane is inflated via a compressor that crushes the marc against the walls, thus releasing its juice: this is called press wine. The rest will go to the distillery to produce state alcohol, which can be sold to produce some very famous aperitifs. Is it better to drink wine than these distilled by-products?
In most cases, the free-run wine is more qualitative, however, qualitative presses will bring fat and pretty aromas to the wines.
The alcoholic fermentation and extraction are then finished, but the winegrower cannot rest yet, it will be necessary to ensure that the second fermentation is carried out correctly: malolactic. Bacteria (leuconostoc) break down malic acid into lactic acid. The first is a stronger acid than the second (two acid functions against one). The acidity decreases during this process, it also gives roundness and aromatic finesse. Once this is done, the wine is considered stable.
You now know the colossal amount of work involved in making a quality red wine, both in the vineyard and in the cellar during the harvest. So do not hesitate to thank all these men and women who work hard to make this fabulous nectar that is wine, and the most beautiful way is to taste the fruit of this beautiful and hard work.
Edouard Cazals (for Les Grappes)