The phenols in wine range from 0.5 grams per liter in white wines to about 5 g/l in red wines, and the phenolic compounds come primarily from the grape seeds, skins and stems. Although small in quantity, phenols are among the most important red wine components because they are responsible for wine color, bitterness, astringency and some odors and flavors. Some phenolic materials are soluble in water, while other phenolic materials are more soluble in alcohol. The pigments and some flavor compounds are soluble in water, so these materials are extracted earlier in the fermentation. On the other hand, tannin is more soluble in alcohol, so tannin is extracted later in the fermentation process after some alcohol has accumulated.

The figure shows how pigments and tannin accumulate as a function of skin contact time in red fermentations. These data show several interesting features. (1) Note that over 90 percent of the total available color was extracted in the first four days of fermentation. (2) Wine color started to decrease after eight days of skin contact time and (3) the color dropped to about 75 percent of its maximum value after 20 days of skin contact. (4) During the last 30 days, there was little change in wine color. These data clearly show that tannin behaves differently than color pigment. Unlike color, tannin continues to be extracted as long as the liquid and solids are in contact.
Wine characteristics are very dependent on phenolic compounds, so winemakers use several techniques to control the amount and kind of phenolic compounds in wine.

Cold Soaking
"Cold soaking" is a common winemaking technique used to produce softer, less astringent, red wines. The process is simple. Sound grapes are crushed and a small amount of SO2 is added. If needed, refrigeration is used to cool the must to 40 or 45 degrees. The crushed fruit is held at the cold temperature for one to several days. The must is allowed to warm up, and then it is inoculated with yeast to start the fermentation. The prolonged skin contact results in considerable color and flavor accumulation, but relatively little tannin is extracted because no alcohol is present. Cold soaking is particularly effective when used on Pinot Noir or any red gapes that are short on color and long on astringency.

Remove Free-run Juice
Much of the flavor producing materials and practically all of the color pigments are in the grape skins. So, simply removing 10 to 15 percent of the free-run juice before starting fermentation can change the solids to liquid ratio and significantly increase wine flavor and color intensity. This is not a new winemaking technique. The process, called saignée (say-NAY), has been used in France for hundreds of years to produce darker colored and more flavorful red wines.

Whole Clusters
Sometimes red grapes do not have enough tannin to provide adequate phenolic structure to the wine. So, a longer skin contact time may be needed to extract more tannin and improve the mouth feel and structure of the wine. In this case, when winemakers are fermenting in open containers, they often retain 5 to 10% whole clusters. Late in the fermentation, a few of the whole clusters are crushed by hand each time the cap is punched down. Crushing the whole clusters adds a small amount of additional sugar to the fermentation. The added sugar produces more carbon dioxide gas to provide oxidation protection.

Cap Management
The way the juice and skins are manipulated during the early part of fermentation is another way of controlling phenolic extraction. Gentle "punching down," done several times a day, extracts more color and less tannin than "pumping over." Consequently, many winemakers prefer to use small, open fermenters, rather than large, closed tanks, for the production of high quality red wines.

Short Vatting
The term "short vatting" is used to describe red wines that are pressed before the fermentation reaches dryness to limit the amount of skin contact. Since much of the color and flavors are extracted early in a fermentation, four or five days of maceration may be enough time to extract these materials from the solids. This is a quick and easy way to produce soft, fruity red wines that can be consumed early.

Pressing Technique
High press pressures produce wines containing more harsh tannin and bitter materials. Low press pressures produce wines containing less of the harsh substances. So, winemakers can control the phenolic content of their red wines by using alternative pressing techniques. Modern, computer-controlled, bladder presses can separate the liquids from the solids effectively by using very low pressures and many press cycles. These presses are popular because they can remove practically all of the liquid and produce dry pomace while extracting smaller quantities of tannin.

Separating Press Wine
Here is another simple technique winemakers use to adjust the astringency of their red wines. During the pressing operation, the heavy, astringent press wine is kept separate from the free-run wine. The two press fractions are aged separately, and then if more astringency is needed later in the winemaking process, the press wine can be blended back into the main lot.

Fining
Fining provides a convenient means of reducing the phenolic content of wine late in the winemaking cycle. Protein materials such as a gelatin, casein, egg whites, etc. are often used. A carefully measured quantity of fining material is added to an overly astringent red wine. The protein material combines with tannin, and both the protein and tannin precipitate out of the wine. Huge amounts of astringency cannot be removed without stripping some color, flavor and aroma from the wine. But, protein fining provides an easy, simple way of "fine tuning" the astringency of red wines.

Summary
Winemakers use several different winemaking techniques to control the amount and kinds of phenolic materials in their red wines. But, predicting the effectiveness of some techniques is difficult and sometimes considerable winemaking experience is needed. This is why making high quality red wine is as much art as science.

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