CORNELL UNIVERSITY

FS430: Understanding Wine and Beer

Calendar

Readings: Jackson pp. 281-295

Slides

Introduction to Winemaking Chris J Gerling Winemakers have many choices to make in modern enology. First and foremost is the choice of what grapes (or possibly even other fruit) to use. American wines tend to include three main families of grapes: Vitis Vinifera, interspecific hybrids, and Vitis Labrusca. Grapes are selected based on the growing conditions and the desired style of wine. Once harvested, grapes can be separated from their stems and seeds, pressed as whole clusters, or left intact to carry out carbonic maceration. Crushed grapes that have not been pressed are called must. The must may be pressed in a variety of ways to extract or not extract certain chemicals found in the seeds, skins and flesh. Winemakers may be allowed to choose to add sugar, a process called chaptalization, to increase the final alcohol content. This practice is illegal in some countries. Nutrients may also be added for the yeast, mostly in the form of Nitrogen sources. Pressed juice may be fermented with a variety of yeasts, one yeast, or left to use the microorganisms already present. If the winemaker inoculates the juice with a pure yeast culture, the yeast will almost certainly be of the Saccharomyces cerevisiae species. Sulfites are added to eliminate other microorganisms (if so desired) and to prevent oxidation. The wine will then be fermented in oak barrels or stainless steel tanks. The winemaker can choose to add a malolactic bacteria culture to carry out a secondary fermentation. Depending on the climate, the amount of acid in the wine may be too high or too low. The level can be adjusted before the wine is put in near-freezing temperatures so any remaining tartaric acid crystals can precipitate out. The wine can be bottled or aged after cold-stabilization.

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