Chapter 6

Wine Fermentation

Carbonic Maceration for Red Wines

Carbonic maceration is a winemaking technique that's applied primarily to light- to medium-bodied red wines to make them fruitier and to soften their tannins. Most wine transforms from grape juice into alcohol via a yeast fermentation but in carbonic maceration the initial fermentation is not caused by yeast, but instead occurs intracellularly, or from the inside out. This is the origin of the name carbonic maceration in which berries undergo intracellular anaerobic metabolism. In this technique the uncrushed grape clusters are placed in a fermentor, which is then sealed. The air in the container is then replaced (purged) with carbon dioxide, thus preventing the grapes from coming into prolong contact with oxygen.

Advantages and Disadvantages

Despite the existence of two distinct phases - carbonic maceration and alcoholic fermentation - carbonic maceration requires less time than traditional winemaking. This method is therefore well adapted for wines that are quickly put on the market. Most carbonic maceration wines are produced for rapid consumption, with only a small proportion vinified for extended aging.

Sensory Effects

Carbonic maceration wines have a distinctive aroma which often polarizes tasters. The aromas can be described as fruity or musk-like, with strawberry/raspberry, and cherry/ kirsch aromas (particularly in Beaujolais wines), but also with vanilla, spice, almond, cinnamon, sandalwood, or oak-like characters.

Phenolic Compounds

The extraction of phenolics, such as anthocyanins and tannins, from grape skins is different during carbonic maceration compared to standard winemaking.

Winemaking Process

The process is composed of five steps: harvesting, filling the tanks with intact berries, maceration, pressing, followed by alcoholic fermentation.

Harvesting

Careful harvesting and handling are crucial for carbonic maceration; the bunches and berries must arrive at the winery unbroken. This means that mechanical harvesting is only an option with tough-skinned varieties.

Filling Tanks with Intact Clusters

The grape clusters are not destemmed nor crushed before carbonic maceration. However, certain varieties, in certain regions, the presence of stems may introduce herbaceous notes and a degree of bitterness during carbonic maceration. Stem elimination should therefore be considered in some cases.

Maceration

Maceration phase, in which the berries undergo intracellular fermentation or anaerobic metabolism, lasts until the berry dies. Death of the grape berry is caused by the accumulation of alcohol or by bursting of the skins due to the weight of the grapes above it and marks the end of the important aroma-producing phase of carbonic maceration. It takes place between five and 14 days depending on the temperature.

Pressing

Once berries burst (or carbonic maceration is halted) phenolics are extracted conventionally. Pumping the must over once or twice before devatting enhances the must's aromatic intensity and tannic structure. During devatting, the grapes should be carefully pressed (Figure 6.12). The free-run juice is allowed to escape, and the remaining juice extracted from the intact grapes and must. If the free-run shows no signs of active malolactic fermentation, it is common to combine all the juice fractions before alcoholic fermentation.

Alcoholic Fermentation

In the last phase alcoholic fermentation, the juice, minus the skins, is inoculated with yeast and completely fermented at 15 to 20 degrees C (59-68°F). Malolactic fermentation typically begins immediately after the completion of alcoholic fermentation, if not before.d to, although not mutually exclusive, punching down or pumping over, the submerged method holds the cap under the surface of the must for a fixed period of time meaning it remains permanently in contact, but not disrupted, with the must.

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