Definition: Extraction (the rules of)

The extraction of grapes is similar to that of tea bags. Both contain aromatic compounds and colouring agents that are extracted from a solid body to impart their characteristics to a beverage. In the case of tea, the infusion of the leaves imparts colour, flavour and tannins to the water.

With red grapes, this identical role comes from the skins, which supplement the juice with these same elements. Both beverages require extraction that is appropriate in terms of duration and strength. A tea bag that is insufficiently steeped or steeped in water that is not hot enough will lack intensity. Conversely, steeping for too long or using water that is too hot can emphasise a harsh, bitter flavour.

Red wine production follows the same scenario. The components that provide colour, flavour and tannins are found in the skins. The extraction of these molecules through various maceration methods is the basis of red wine production processes. The term maceration is often used as a synonym for extraction, although maceration is the means and extraction is the result.

First and foremost, it is the character of the grape and the winemaker's objective that determine this approach. In general, the aim is to maximise the intensity of the fruit while minimising the negative effects of harsh tannins, excessive acidity and unappetising flavours.

The surest way to achieve this is to use ripe, top-quality raw materials. Extraction techniques using raw materials of such high quality will influence the desired style. If the type of wine sought is fruit-based and intended for early consumption, such as Beaujolais Nouveau, tannin extraction will be avoided as much as possible. On the other hand, to produce a wine for ageing that will evolve favourably over decades (great Bordeaux, Barolo), maceration will be very thorough. Grape varieties such as Cabernet Sauvignon and Syrah tolerate more aggressive maceration techniques, while others, such as Pinot Noir in particular, require a gentler approach. However, regardless of the grape variety, there are always undesirable elements in the wine.

Three main factors will determine the final result:

1) The condition of the grapes in relation to the liquid. It is much easier to extract colour, tannins and flavours from grapes crushed in their own juice than from whole berries.

2) The temperature of maceration.

3) The duration of this maceration. These maceration and extraction processes begin in the press immediately after harvesting. Two initial decisions must be made by the winemaker: whether to destem or not (keep only the fruit or keep the whole bunch); keep the berries whole or crush the harvest.

Today, destemming red grapes is the most common process in modern production. Varieties such as Cabernet Sauvignon and Syrah have thick-skinned berries, so the grapes do not suffer too much from destemming. Pinot Noir, on the other hand, is fragile and the crushed berries release juice. It is therefore more common in Burgundy and the northern Côtes du Rhône to vinify grapes that have not been destemmed or have been partially destemmed. The latter technique is becoming less and less common because it is controversial. Its supporters insist that ripe bunches increase the proportion of tannins and contribute to pleasant spicy and vegetal flavours. The bunches slow down fermentation, which tends to be rapid with Pinot Noir, by slightly reducing the temperature in the vat. On the other hand, opponents of destemming fear overly green, herbaceous tannins and less intense colouring, as the bunches absorb colour pigments. Depending on the desired intensity of extraction, winemakers prefer a variable proportion of whole berries. Therefore, destemming and partial crushing of the grapes may be used.

Many producers use an extraction technique called cold pre-fermentation. This involves leaving the skins to macerate in their juice at a low temperature, which delays the start of fermentation. Thus, grapes harvested early in the morning can remain in refrigerated vats for several days. This method extracts colour and water-soluble aromas, but very few tannins, which are only released in alcohol. A temperature of 12 to 13°C, with a little sulphur and a blanket of carbon dioxide, prevents oxidation. Some winemakers believe that this cold pre-fermentation should not last more than 4 days. Beyond that, the protective dose of SO2 becomes too high and can release bitter tannins. It is better to let fermentation occur spontaneously.

When the yeasts begin to convert the sugar in the grapes into alcohol, carbon dioxide (CO₂) is produced, which carries the solid particles to the surface of the liquid, forming what is known as the cap. As soon as these solid particles are no longer submerged in the fermenting must, and depending on the heat, they no longer produce the desired extraction.

It is at this precise moment that the winemaker can choose between two traditional techniques developed in Bordeaux and Burgundy: pigeage, which consists of thoroughly submerging the cap by pushing it downwards; and remontage, which consists of pumping juice to soak the cap.

The frequency of these techniques depends on the grape variety, the terroir and the vintage. Extremes can range from 3 to 50 times, with up to 4 times a day at the peak of fermentation. Today, modern winemaking techniques allow for richer fruit and softer tannins because we know how to approach extraction techniques more gently.

Temperature also has a significant influence on both fermentation and extraction rates. Heat makes the skins very delicate, even breaking them down, which makes extraction easier. Another factor is that the higher the temperature (up to a certain limit), the faster the chemical reactions.

Most winemakers maintain fermentation temperatures for red wines between 20 and 25°C, but we have encountered cases where the temperature of a Syrah has been raised to 36°C, which can kill the yeasts but shortens the extraction time and prevents the over-extraction of unwanted coarse tannins. Other producers prefer to leave wines with a long ageing potential in contact with the solids until the end of fermentation and even beyond. This post-fermentation maceration technique is common in Bordeaux, but has gained followers all over the world. The general consensus is that this method essentially releases the tannins that are soluble in alcohol, while the post-fermentation technique has little impact on colour and aromas, as most of these components have already been extracted at the beginning of the extraction process.

Winemakers often decide when it is time to move on to pressing by tasting the wine, glass in hand. This important decision is not made in front of a computer screen!