Destemming separates the grapes from their stems. If the stem is not sufficiently ripe it could inject unpleasant or green tannins into the wine, or a grassy taste. The stems may be retained, however, if they are mature enough to enrich the wine’s palette of aromas, to add quality tannins to a wine that is lacking or to be cellared, or to add extra complexity. This is the case for example in regions such as Beaujolais, Burgundy and Languedoc-Roussillon.
The principle :
- Transforming grapes into wine by fermenting sugar into alcohol.
- Injecting tannins and red colouring agents from grape skins into the juice, by maceration.
The purpose of crushing is to make the grapes burst open and release their pulp and juice. This helps the fermentation process and above all releases the colour contained in grape skins. Pulp does not contain any pigments (apart from Poulsard grapes).
Oxygen triggers the fermentation of must. Yeast (Saccharomyces cerevisiae) rapidly transforms sugar into alcohol at temperatures that must not exceed 35°C. Fermentation ceases once there is no sugar left to be transformed. Maceration can last from a few days to several weeks, depending on the quantity and the quality of the tannins, producing wines with different levels of body, concentration and colour. Stirring during the fermentation phase brings the solids (pips and skin) that contain colour and tannins into contact with the juice. This process is called pigeage (punching down the cap).
By the end of the maceration phase, there are two parts to the wine in the vat and they are separated: a liquid part, the so-called "free-run juice" that naturally drains downwards, and the pressed juice that comes from the solid must that needs to be pressed. Press juice has more colour and more tannins. It is less delicate but more concentrated. It will or will not be reincorporated, depending on the type of wine being produced.
The onset of malolactic fermentation by lactic acid bacteria depends on temperature. It may take place directly after alcoholic fermentation in some regions, or it may only begin in the spring, once the temperature in the cellar starts to rise. It transforms the slightly hard malic acid into softer, rounder, lactic acid. The transformation makes wine supple and less aggressive.
Blending is carried out by the winegrower and the oenologist. This process gives rise to the final wine, using wines belonging to the same appellation. The goal is to increase complexity and aromatic richness by using different grape varieties. The blend is the winegrower’s signature. It calls for sensitivity and jealously guarded know-how. The blend is different every year, giving wine its character.
Maturation is an important phase during which a certain number of components of the wine will combine to give a richer wine that is more pleasant on the palate and also more suitable for cellaring in certain cases. Maturation takes place either in a vat – for fruity wines to be consumed while they are still young – or in contact with wood, to accentuate the palette of aromas. Maturing on lees involves maturing a wine without separating it from its deposits in order to keep all of its roundness and aroma.
At the end of the maturation phase, the wine is bottled in very strict conditions of hygiene. It may be filtered beforehand.