The purpose of crushing is to extract the juice from the grapes. Before the grapes are crushed, however, leaves, large stems, and stalks are removed. Some wine makers may not remove all of the stems to increase the concentration of tannins and other phenolic compounds that are present in the stems and extracted into the juice. Once the extraneous material is separated and removed, the grapes are crushed by one of several types of devices. Roller crushers consist of a pair of stainless steel cylinder-shaped rollers. Another type of crusher, called the Garolla crusher, not only performs the crushing step, but also removes stems. It consists of a rotating shaft contained within a large horizontal stainless steel cylinder or cage.Arms on the shaft are attached to paddles or blades such that when the shaft turns, the grapes are moved and pressed against the side of the cylinder. Perforations on the walls of the cylinder allow for the juice (along with the skin, seeds, and pulpy material) to pass through into collection vats, whereas the stems gather at the end.
The crushed grape material, as noted above, contains juice, seeds, and skins. Pigments, tannins, and other phenolic compounds are located in the skins and seeds, and their extraction into the juice takes time. Endogenous pectinases and other hydrolytic enzymes within the grapes enhance extraction and must also be given time to work. This extraction step, where the crushed grape material is allowed to sit, is referred to as maceration.
Maceration conditions are not the same for all wines. For red wines, where pigment extraction is especially important, long maceration times at high temperatures are usually employed. In general, maceration is done at around 28°C for up to five days. The shorter the maceration times and the lower the temperature, the less material will be extracted. Thus, lighter red wines, such as Beaujolais, are macerated for just a few days at no higher than 25°C. In contrast, deeper red wines, such as Bordeaux, are macerated for up to twenty-eight days at 30°C. Since fermentation begins shortly after the grapes are crushed, maceration and fermentation essentially occur at the same time. In fact, the ethanol made by fermenting yeasts enhances extraction.This situation only occurs, however, if the musts are not treated with sulfur dioxide (see below).
As noted above, maceration at low temperatures (<15°C) ordinarily results in only moderate pigment extraction and little fermentation. However, if the must is macerated at a low temperature (between 5°C and 15°C), but for longer time, extraction of anthocyanins and aroma and flavor compounds can be enhanced. This technique, called cold maceration, simulates the natural conditions in cooler wine-producing areas, such as the Burgundy region of France. For white wines, the maceration step is done at lower temperature and for much less time.Typically, only a few hours at 15°C is sufficient. For most white wines, the producers remove the seeds and skins immediately after crushing. As for red wine, the maceration conditions used for white wines influence the amount of pigments and tannins that are extracted.Wines made from Sauvignon blanc grapes where little maceration occurs typically have a low phenolic concentration, whereas Riesling and Chardonnay musts, which are often macerated in the cold, may contain appreciable amounts.
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