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| Grape growing, winemaking and wine maturation |
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| Making red wine |
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 Black grapes for the production of red wine are usually crushed prior to fermentation. This is most often accomplished at the same time as destemming. Some winemakers, however, retain a portion of stems in order to add tannin to the resultant wine. These tannins can be harsh, however, if they are not completely ripe. Stems in the fermentation tank, however, make fermentation easier to conduct because they help the fermenting must to flow and drain through the marc or mass of grape skins.
Some winemakers also appreciate the effect that some whole berries in the must have. The sugar in the berries is released only when the grapes burst during fermentation, and is thus released gradually. This can improve the fruit component of the wine, and many Burgundian producers will leave a proportion of whole clusters during fermentation.
There is a technique called carbonic maceration that calls for all of the clusters to be left whole. In this variation on fermentation, the whole clusters are carefully placed in the tank and blanketed with nitrogen. Fermentation begins within the berry itself under the influence of enzymes in the grape. This special enzymatic fermentation is known as intracellular fermentation. It creates deep color and a pronounced fruit aroma, but almost no tannins. For this reason, it is often used for easy-drinking early consumption reds. The classic case is Beaujolais, which is often vinified using carbonic maceration. After several days of intracellular fermentation, the berries burst and the fermenting must comes in contact with the yeasts on the outside of the grapes. Regular alcoholic fermentation then commences.
In truth, there is always some juice at the bottom of the tank that ferments in the normal way even with carbonic maceration, because the weight of the grapes will crush those at the bottom; there is also always some carbonic maceration taking place when whole clusters are added into a regular fermentation.
Red wine musts are subject to the same additions as described for white wine above. In addition, they often undergo a maceration (known as a cold soak) on the skins under reduced temperature prior to the beginning of fermentation. This is done to improve the color of the resulting wine, because color (in the form of anthocyanin) is water-soluble phenolic compounds that are best extracted at cool temperatures. Sometimes this occurs naturally in a cool cellar, since the must needs to be warmed slightly to cause fermentation to commence. Other times, the must is sulfured and refrigerated in order to prolong this extraction up to a week or even longer.
Once the prefermentation maceration (if any) is finished, fermentation can begin, again on indigenous or cultured yeasts. Here the fermentation is normally carried out between 26–30° C, although again there can be considerable variation.
The main difference between the fermentation of red and white wine is that it is necessary to extract color and tannin from the skins of black grapes during red wine fermentation. Both are contained in the skin of the grape, the juice of most varieties being colorless. Coloring compounds and tannins are both types of phenolic compounds, or polyphenols. They are best extracted in different ways, however.
Extraction of tannins is more complicated than the extraction of color. The first reason for this is that it is important to extract the right type of tannins. Tannins are molecules that create astringency in the mouth because they react with the protein in saliva and render it insoluble. Tannin molecules link together to form chains, and this astringency is compounded when the chains of tannin molecules are short, giving what is called unripe, green or harsh tannins. This is the result of unripe grapes where the acid and sugar may be at the right levels, but the polyphenols have not matured. It can also be the result of harsh extraction. Silky tannins are produced, on the other hand, through picking physiologically ripe fruit and extracting the tannins very gently.
Since tannins are more soluble in alcohol than in water and more easily extracted at higher temperatures, extraction occurs most effectively once the fermentation has gotten under way. One method is to pump the juice from the bottom of the tank and let it drain through the cap of skins that is floated to the surface by the CO2 produced by the fermentation. This also keeps the cap moist and helps prevent the development of volatile acidity.
 For some thin-skinned grapes such as Pinot Noir and Nebbiolo, there are winemakers who see pumping over as a relatively harsh method of extraction. These winemakers prefer to punch down the cap to break it up. Still others use a combination of pumping over and punching down.
Another method is déléstage or “rack and return”. In this procedure, the fermenting must is tank is drained into another tank and then slowly fed back into the tank containing the skins, stems and seeds (called pomace or marc). This is a method that is both highly effective and fairly gentle.
At the other extreme, there are methods that extract more polyphenols but are rather harsh on the wine. One method is to heat the grapes before they are crushed (thermovinification), which can impart a cooked aroma and flavor to the wine. This method is used for inexpensive wines.
Another method is the use of rotofermenters, or rotating tanks that keep the marc constantly mixing with the must. This valuable tool can sometimes be overused, producing awkward, overextracted and out-of-balance wines.
Winemakers in Port use autovinifiers, which are non-electrical tanks that rely on the pressure of the CO2 generated by the fermentation to draw wine up a pipe, from which it will be sprayed over the pomace when the tank reaches a certain fill level.
The vessel used for fermentation is important for red wines just as it is for white wines, although small 225 liter casks are almost never used, since it is difficult to get the pomace into them. Wooden vessels of different sizes are used quite often, however. The alternatives are the same as for white wines: temperature controlled stainless, concrete or lined steel.
Once the fermentation has ceased, red wines are often left to macerate on the skins for a period that may last anywhere from a few days to a month. Extraction continues during this phase, and excessive maceration can also lead to overextraction. As with fermentation, the more polyphenols are extracted at higher temperatures.
After maceration, the pomace is pressed, and the wines undergo their malolactic fermentation. It is most common to keep the press wine separate from the free run juice until blending. During the blending process all, some or none of the press wine will be added to the blend. It is very rich in polyphenols, but it is somewhat lacking in fruit. The effect on the wine, then, can be to add harshness without elegance if press wine is used to excess.
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Wine Regions of the World
