Autumn is here and, as the leaves turn color and fall from the trees, many a young man and woman find their thoughts turning from white and rosé to red... red wines! Many of the light, crisp, lively white wines and crisp rosés that we love to drink chilled on a hot day simply don’t seem as enticing once the leaves are on the ground and sweaters come from the closet. Many of the foods we eat during the colder months naturally call for a red to accompany them, too. Think: stews, roasts, braises, daubes!
Red wine, like all alcoholic beverages, is made through fermentation. In fermentation, yeast converts the natural sugars in grapes into ethyl alcohol, giving off heat and carbon dioxide as byproducts. Anyone who has worked with yeast, as in home bread making, knows that yeast responds to temperature. Too cool and fermentation slows down. Too hot and the yeast dies, stopping fermentation. One of the reasons that modern winemaking is done in stainless steel tanks is that it is easy to control the temperature of the fermenting must inside them. (Must is the combination of pressed, unfermented grape juice along with pulp, skins, stems and seeds from the grapes. These “other” components are also called pomace.) Cool temperature fermentation takes longer, but generally produces lighter, more aromatic wines. Warmer fermentations are faster, and result in big, full flavored wines such as Châteauneuf-du-Pape. Fermentation proceeds until one of three things happen:
1) All or almost all of the sugar in the grapes has been converted into alcohol, resulting in a dry wine (no sweetness).
2) The alcohol level has become high enough to kill the yeast that has been creating it. This can occur whether there are sugars left in the must or not.
3) The wine maker stops the fermentation before all of the sugars have been converted into alcohol. This will leave some sugar, called residual sugar, in the finished wine. This is usually done by chilling the wine and filtering out the yeast. With fortified wines, brandy is added to kill the yeast and keep a high level of sugar in the wine.
There are countless strains of yeast, and each has its own characteristics. Some can survive in fairly high concentrations of alcohol, and are used for making wines where the wine maker wants a wine with 14 or 15 percent alcohol. There are strains of yeast that will die once the alcohol level in the wine they are making reaches a bit over 12 percent. Use one of these yeasts with grapes that are very ripe and high in sugar and you will end up with lots of residual sugar: a wine with noticeable sweetness. Yeast also affects the taste of the finished wines, which leads many wine makers to import yeasts from other areas, hoping to influence the flavor of their wine. Biodynamic wine makers refuse to do this, believing that the sense of the “terroir” of the vineyard is best expressed by relying on the yeasts that live in that vineyard along with the grapes.
Since the pigments that give red wine its color are in the skins, the juice of red grapes is fermented along with the grape skins. Whole bunches of grapes are normally destemmed, since the harsh tannins and other bitter chemical compounds in the stems would give the finished wine a “green” and harsh taste.
Tannin is a natural preservative, found in the skins, seeds and stems of grapes. It also occurs in tealeaves, coffee beans, tree bark and in the oak barrels that wine makers often use to age wines. Tanning, the process of turning animal skins into leather, gets its name from the tannic acid that it uses. In tanning, the skins are soaked in a tannic solution that keeps the skins from rotting. The presence of tannins in red wines preserves them, too, and is the main reason that red wines can age longer than most white wines. Tannins have a natural drying effect that you can feel on the sides of your tongue. The presence of tannins, with their natural affinity for linking with proteins, is the reason why red wines are a much match for drinking with red meat and grilled meats.
With time, the tannins and pigments in red wine will link up in the bottle with assorted other chemical compounds and form long, heavy molecules called polymers. As these molecules form, they are no longer in suspension in the wine, so the wine “matures”, becoming smoother, more rounded and complex in flavor. This is why the finest red wines are best when aged, for years or for decades. Red wines with sediment are best served after decanting them, leaving the sediment behind in the bottle. For more on this, see my column on Decanting and Decanters.