The winemaking process comprises a number of stages which diverge at certain points depending on whether the wine is red, white or rosé.
The white winemaking process
On arrival at the winery, the harvested grapes are crushed. The purpose of this operation is to make the extraction of juice at the pressing stage easier.
After crushing, they are weighed and then sampled to measure the sugar level. These quantitative and qualitative measurements are necessary to comply with federal and cantonal legislation, to correctly compensate winegrowers according to their harvest, and to compile various internal harvesting statistics.
The grapes are then transferred to a press where the must is extracted. At the end of this cycle the grape pomace, comprising the vegetative parts of the grapes (stalks seeds and skin), is removed from the press and composted, and sometimes even fermented and distilled.
The must is taken back to the winery for clarifying. This step involves separating the cold grape juice from solid impurities such as fragments of skin, seed and other types of residue. This process has an important impact on the quality of the wine.
The next step is the addition of yeast. Adding a selected strain of yeast helps start the fermentation process and ensures its good development. The alcoholic fermentation takes five to ten days, during which time the yeast converts the sugar to alcohol.
Some two weeks after the end of the fermentation process, the new wine is transferred to another vessel and separated from its lees, principally made up of dead yeast cells.
In the weeks that follow, the malolactic fermentation (MLF), or so-called secondary fermentation, is performed. During this period the lactic bacteria, naturally present in grape must, will convert the wine’s malic acid to lactic acid. Since lactic acid is half as acidic as malic acid, the fermentation brings about a substantial fall in acidity and an increase in pH levels.
This change in pH level leaves the wine extremely vulnerable. It needs to be rapidly protected by a moderate addition of sulphites, called chemical stabilisation, which safeguards it against premature oxidation and microbes that could otherwise spoil it.
The wine is then cooled and kept at a temperature of about 0 °C for six to eight weeks. This process, called physical stabilisation, brings about a natural clarification of the wine and also assists the precipitation of tartaric salts, which avoids the formation of tartaric crystals in the bottle.
At the end of this process comes the pre-filtration phase when the wine is separated from suspended particles left over from previous processing.
Once this step has been performed, the temperature of the wine is brought back up to 10° to 12°C. It then undergoes a last filtration before bottling.
The red winemaking process
The winemaking process for red wine diverges from that of white wine.
Red grapes intended for fermentation are not only crushed but also de-stemmed. In our latitudes this operation, which separates the stalks from the grapes, helps limit the extraction of aggressive and bitter tannins during maturation.
After weighing and sampling, the crushed and de-stemmed grapes are not transferred to a press, as would be the case with white grapes, but placed in a vat with the addition of sugar and yeast for fermentation.
The fermentation phase, when the whole crushed grapes macerate, lasts about ten days. During this period, the alcohol is formed, the temperature rises and the must is pumped over (the cap of grape skins floating on the surface of the must is stirred up and leached), thus permitting the red wine colour and tannins to be extracted.
When the alcoholic fermentation ceases, it is time for racking. This operation is carried out in three steps. First the new wine, called free-run wine, is separated from its lees by pumping it off to a new container. The cap of grape skins is then racked off and taken to a press for pressing after which it is composted or distilled. Lastly, the press wine (rich in tannins extracted from the pomace during the pressing) is transferred to another container and blended with the free-run wine.
After that, the winemaking process is the same as it is for white wines - except for one difference. Red wines undergo more transferring from one vessel to another in order to expose it to oxygen and thus eliminate the carbonic gas formed during the alcoholic fermentation process.
The rosé winemaking process
The vinification process for rosé wines (made from red grapes) is similar to that of whites. The key difference is that after crushing, weighing and sampling the grapes are macerated for a few hours, just long enough to extract the desired colour before they are pressed.