Winemaking with red grapes differs substantially from the two previous processes. Fermentation takes place in the presence of the skins, to extract the substances contained in them (primarily tannins and anthocyanins).
In most cases, the grapes are destemmed, because, although the stems contain tannin, they also add bitterness and astringency. The berries are crushed, and after the addition of a light dose of sulfites, the must is sent to the fermentation tank. From the very beginning of fermentation, carbon dioxide raises the solids, which form a compact mass at the top of the tank called a “cap.”
In the tank, alcoholic fermentation takes place at the same time as maceration of the skins and pips in the must. The complete fermentation of the sugar (if there are no problems) lasts 5 to 8 days. To prevent the death of the yeast, the temperature cannot be allowed to exceed 86 ºF / 30 ºC. Maceration gives the wine its color and tannic structure. Wines that are to be aged should be rich in tannins and therefore undergo a long maceration (2 or 3 weeks) at a relatively high temperature, between 68-86 ºF / 25-30 ºC.
“Pumping over” allows us to monitor the extraction of the constituents in the skins. This operation involves pumping the juice at the bottom of the tank to the top onto the top of the cap, exposing more of the juice to the skins and extracting tannins and anthocyanins.
Racking involves separating the free-run wine from the solids (which are also called “pomace”). The pressing of these solids results in press wine, which is very tannic and deeply colored. If we are developing a wine for aging, it is very common to mix the press wine with the free-run wine to give structure and intense color. If wine is to be consumed young, it is not mixed, because mixing provides a certain astringency that requires years of aging to soften.
Malolactic fermentation is a necessary step in making red wines. Ideally, while it is being racked, the wine is not allowed to cool below 64 ºF / 18 ºC. If all goes well, after two or three weeks the wine will again become saturated with carbon dioxide, a condition that indicates the start of the malolactic fermentation. This process ranges from one week to one month (even longer if the cellar is very cold); when it is completed, the wine is decanted and sulfites are added.
Carbonic maceration is a particular way of making red wine which has a great tradition in the region of La Rioja (the popular cosechero or nouveau-style wines).
The main departure from conventional winemaking is that it does not involve breaking the skins of the grapes before fermentation, meaning that the grapes are neither de-stemmed nor pressed. Because of this fact, carbonic maceration is also referred to as whole-cluster fermentation. Whole bunches of grapes (which must be manually harvested) are loaded into the fermentation tank until it is filled. Immediately thereafter, carbon dioxide is pumped into the tank from the bottom. Being heavier than normal air, the carbon dioxide replaces all the oxygen in the tank from the bottom up, and the grapes are left surrounded by an entirely anaerobic atmosphere composed only of this gas.
In this environment of pure carbon dioxide, the grapes develop a special metabolism which begins to transform part of their sugars into alcohol. This transformation is not due to the development of the usual microorganisms, yeasts, but is instead due to the metabolism produced by the grapes’ own enzymes at an intracellular level inside each individual grape.
In addition to producing a small amount of alcohol (about 1.5 percent), a series of characteristic aroma components are synthesized, such as notes of sour candy, fruit yogurt, banana, etc. These components are easy to detect and identify, as can be confirmed by tasting any wine produced by this particular method. The winemaking technique consists of two parts: