Chapter 6

Wine Fermentation

Post-Fermentation Management for Red Wines

The winemaker has a number of timing options when separating the wine from the skins after fermentation. Some winemakers prefer an early pressing before the wine has fermented completely dry if must had a high tannin content or of the goal is to accentuate fruitiness. The wine will finish primary fermentation in tanks or in barrels, and tannin extract will end at pressing. Another option involves waiting until active fermentation has substantially ceased, at dryness. Many winemakers find this a safe decision - no further fermentation in tank or barrel to manage, with low tannin levels. Alternatively, the winemaker can wait until cap falls allowing the skins that make up the cap to literally sink to the bottom of the fermentor allowing for more tannin extraction.

Extended Post-Fermentation Maceration

Depending on the style required, the wine may be left to soak with the skins (and, sometimes, seeds and stalks) after completion of the alcoholic fermentation, to improve color stability, flavor, and tannin structure of the wine. As maceration time increases, so does the extraction and polymerization of phenols to form higher molecular weight tannins. This is reflected in the sensory analysis: reduced, yet stable color, and more, yet softer tannins. The increased extraction and polymerization of phenols during extended maceration produces wines that are round and firm in the palate often with considerable aging potential.

Length of Maceration

The length of post-fermentation skin contact is determined by a variety of factors, including fruit maturity (perceived presence of ripe tannins), source of fruit, history of wines produced from that source, stylistic goals, and taste. Grapes from some vineyards benefit from extended maceration, but not others. This may represent qualitative and quantitative differences in grape phenols.

Management Practices

Extended post-fermentation maceration is usually conducted in the same vessel in which the wine was fermented, meaning that additional fermentation capacity is needed if the technique is adopted. It is typically conducted in a closed system with little air exposure because any solids floating on the wine can facilitate Acetobacter growth and acetic acid formation under aerobic conditions.

Pressing

A decision to press the must is made according to the desired wine style, when an optimum amount of color, flavor, tannins, and other constituents are extracted. Pressing the must occurs after the free-run wine has been removed from the fermentation tank and takes place when the winemaker believes that the required amounts of color, flavor, and tannin have been extracted (Figure 6.15).

Composition of Press Wines

Between 10 and 15 percent of the total juice comes from the pressing process. Its volume during winemaking depends on the level of pulpiness of the grapes. This wine is very different from free-run wine and much more difficult to extract. The volatile acidity of press wine is always higher than in free-run wine and total wine acidity is generally also a little higher. More phenolic compounds (e.g., anthocyanins and tannins) are present, reflected in the extract values.

Settling Tanks

Some winemakers prefer to allow the wine to settle in a tank prior to undergoing maturation. Temporarily putting the wine in tanks has a number of advantages. First, it presents an opportunity to blend the wines. Second, it is easier and more rigorous with a limited number of large tanks than with a greater number of small barrels.

Blending Press Wines

The decision to blend press wines with free-run wines is complicated. It not only depends on both free-run and press wine quality but also on the type of wine desired. In general, press wines are not added when making tablestyle wines for early drinking, except when the press wines are excessively light.

Devatting

When the free run juice has finished fermenting and has become wine, the winemaker separates the free run wine by from the pomace (or marc) - the solid remains of the grape. With the help of a pump and gravity, the free run wine is transferred into another tank or into barrels. When run off is complete, all that remains is the pomace that is pressed to extract the press wine, a wine of lower quality that the winemaker might choose to add to the free run wine.

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