The vinification of white wines is an art, requiring a great deal of attention throughout the process, from the harvesting of the grapes to the maturing of the wine. We will help you to see it more clearly thanks to this didactic guide.
A few reminders for the record. You regularly read or hear words like "yeast", "chaptalisation", "sulphur", "bâtonnage", "oxidation", "stainless steel vats", etc. when you visit a winemaker. These terms that describe the stages of wine making often give indications on the style of wine you are going to taste, its texture, its fruitiness, its taste, etc. We will therefore try to decipher some of these expressions for you, so that you can better understand their hidden meaning, especially concerning white wines today. Let's also remember that everything starts with grapes and therefore in the vineyard. And that we will start from the assumption that the grapes of our future white wines are of good quality, because if it is possible to produce bad wine from good grapes, it is impossible to make good wine from bad grapes!
Some general principles to start with. Most white wines are made from white grapes. But not only that... In fact, the vast majority of black-skinned (or rather very dark red) grapes have, like white grapes, white juice. If we press these black grapes without letting the skins macerate, we will obtain white or barely "stained" juice as we say in oenology. Everyone knows the champagnes produced from pinot noir or pinot meunier, whose colour is almost the same as those made from pure chardonnay and which are called "blancs de blancs" to indicate the grapes that produced them.
The vinification of white wines is then globally more technical than that of red wines. The most delicate aspect is the preservation of fruit, freshness and acidity, key points in the appreciation of most white wines. As soon as the grapes are picked, the risk of oxidation is very high and its consequences are much more noticeable on the taste of the future wine than in the case of red wines, which have a greater margin of tolerance. To avoid this risk, it is often preferable to harvest the whites very slightly under-ripe because a very ripe harvest weakens the skin of the grapes. This is also why, in hot regions, white grapes are sometimes harvested at night or as early as possible in the morning. The question of transporting the grapes from the vineyard to the press is also essential: the use of small containers (crates) to avoid damaging the grapes and the length of transport are essential here.
Pressing without rushing
The first choice of the winemaker is either to press the grapes that have just arrived at the winery immediately or to carry out a short cold skin maceration. In this case, the grapes are completely destemmed and then left to macerate in the cold for 12 to 48 hours, with the crushed grapes remaining in contact with the skins in order to extract a maximum of aromas. Skin maceration gives the whites a more pronounced fruity and varietal character and reinforces the aromatic contribution. The length of this maceration allows the intensity of the fruity character that the winemaker wishes to give to his wine to be determined.
The second key moment is the pressing. And in particular its progressiveness and the gentleness (slowness) with which it is carried out. Pressing that is too "violent" risks giving herbaceous tastes and above all crushing the pips, which could release bitter and vegetal flavours. Today, horizontal presses are used, and increasingly pneumatic presses (with a membrane that inflates to progressively crush the grapes) which allow a better distribution and above all a very precise dosage of pressure. But some traditional winemakers like to use old vertical presses which they think are more precise (there are still many in Champagne).
Whatever the type of press, the winemaker can carry out several successive pressings, increasing the pressure each time. Sometimes only the first pressings are used, the last pressings, of lesser quality, being downgraded to table wine or being added only very partially to the final blend after being vinified separately.
At this stage, the pressed juice is a beige/brown liquid that still contains a lot of solids. To produce a good white wine, fermentation must take place with clear juice. The winemaker will then proceed to what is called "débourbage" which consists of eliminating all the particles in suspension. This operation is most often done by gravity, by collecting the lees at the bottom of the tank, or sometimes by centrifugation, a much more violent method that is only used for wines of lesser quality.
This brings us to the stage of alcoholic fermentation. As with red wines, this fermentation can start spontaneously with the so-called "indigenous" yeasts that are naturally found on the skin of the grapes or in the cellar. Otherwise, the winemaker can choose to use "selected" yeasts, either produced from yeasts chosen once and for all and reproduced in the laboratory, or bought from laboratories. These yeasts can sometimes be used to artificially enhance the aromas, reinforcing the very "sauvignon" side of a Sancerre or exaggerating the buttery aromas of a Chardonnay. But this is no longer the world of great wines...
In any case, the aim is to obtain a rapid and above all controlled start to fermentation. Yeasting (with neutral yeasts if possible!) is often more frequent than in the vinification of red wines. Indeed, in white wine vinification, the juices remain in contact with the skins for a short time, which are the main source of indigenous yeasts.
The fermentation of a white wine must take place at a low temperature (between 18 and 20°) in order to preserve the aromas of the fruit. It generally lasts from 10 to 14 days. At lower temperatures (12-13°), there is an increased production of esters and aromas but the wines are lighter and less rich in glycerol. The temperature of fermentation is therefore chosen according to the type of wine desired. Of course, the lower the temperature, the longer the fermentation will take. This can take up to a month, especially if you want a very dry white wine and you have to wait for all the residual sugar to be transformed into alcohol. It is therefore important to control the fermentation temperatures. For this purpose, stainless steel tanks are cooled by running cold water over the walls. It is also possible to cool by passing through a cooler or immersing a "flag" in the tank.
Malo or not malo?
At the end of the alcoholic fermentation, the winemaker is often faced with a new choice: to let it happen or to prevent a second fermentation called "malolactic" fermentation. This second fermentation, often very discreet, transforms the malic acid naturally contained in the grapes into lactic acid. As lactic acid is less aggressive, it is less noticeable in the mouth than malic acid. We can guess that for "small" white wines to be drunk on their fruit and freshness, the winemaker will have every interest in preventing this second fermentation. The same problem applies to certain southern wines whose natural acidity is often quite low. Conversely, the winemaker who is looking for a certain complexity, fatness and roundness in his white wine will tend to let this fermentation take place or to facilitate it. To block any possibility of malolactic fermentation, the usual solution is to add a dose of sulphur to the must at the end of its fermentation. To facilitate it, the same must can be slightly heated (or selected bacteria can be added, but this is less natural...). Most of the best estates let nature take its course. Some years the "malo" is done, some years it is not, and it is very good to let the elements do their work!
Then the wines are racked (possibly lightly filtered) and poured into a new container to be aged. To obtain more fat, some wines are matured on the lees and sometimes even stirred to put the lees back into suspension, but this process, which was very fashionable at one time, particularly in the Côte d'Or, is now more debated. Like red wines, white wines can be aged in vats (stainless steel, resin or concrete) or in wooden containers or even in amphorae.
The key issue of sulphur
Before closing the discussion on white wine vinification, let's add a little more detail on the use of sulphur in the process. As we have already said, white wines are more fragile than red wines, and in particular they are more sensitive to oxidation, starting with the harvest. Sulphur is the winemaker's number one weapon against oxidation. This is why he can use it quite often during the vinification of his whites by adding it as soon as the grapes are harvested and then throughout the vinification process, in particular during the various rackings (when the must is transferred from one container to another), right up to bottling. This is why the same winemaker, whatever his style (very traditional or closer to a natural style) will always tend to put a little more sulphur in his white wines than in his red wines (whose tannins play a protective role).
The problem is that sulphur, which can be a wine's best friend in protecting it, can also be its greatest enemy! Its slightly excessive use has two major drawbacks: the first is that in high doses it is poorly tolerated by the body (from headaches to allergic reactions) and the second is that it alters the taste of wine, especially white wine. Not only by giving it an aroma ranging from a match in the making to hints of rotten egg, but above all by "compressing" the aromas, by smothering their fruitiness in a kind of straitjacket from which the wine never really breaks free even after long cellaring.
For the winemaker, it is therefore a question of skill and above all of attention. By working his vineyard well to obtain healthy grapes at harvest time, by maintaining very reasonable yields to obtain well-concentrated juices, by taking care of the sorting of the berries before vinification, by ensuring irreproachable hygiene in his cellar, by manipulating his wines as little as possible during vinification (in this respect, stirring the lees is not exemplary...) and by not blocking a possible malolactic fermentation, sulphur will only become a small, reassuring safety device for the winegrower (and the future consumer! ). The regulations authorise 200 mg/l of total sulphur for dry white wines (150 mg/l for organic wines), which is actually enormous. A good winemaker, under the conditions detailed below, can without any risk go well below 100 mg/l for his whites, or even much less (perfectly stable whites can be found with 50 mg/l of total sulphur). Of course, we are talking about "total sulphur" here, i.e. all that has been added since the harvest until bottling. The so-called "free sulphur" (what remains in the bottle you buy) is much less important because a good part of the sulphur added during the wine-making process combines chemically and therefore disappears as such. Nevertheless, the more total sulphur there is in a wine, the more free sulphur remains at the end of the chain...