1. Crushing and Destemming: Grapes are fed into a machine which crushes them between rollers and removes the stems. The remaining mass of juice, pulp, seeds and skin is known as “must.”
2. Fermentation: Yeast converts the sugar in the must into alcohol and carbon dioxide gas. Yeast naturally occurring on the grape skins can be used, or cultured yeasts can be added. Sugar and/or acid might also be added if the grapes are not sufficiently ripe or lack acidity. In the production of red wine, the contact that occurs between the must and the skins releases color, tannins and flavor compounds.
3. Pressing: In the production of red wine, when there are sufficient color, tannins, flavor and alcohol, the liquid (free-run juice) is removed and placed in a separate container. The matter remaining in the tank (pulp, seeds, and skins) is pressed producing a thick dark liquid known as “press wine,” which may be added at the blending step to increase tannin and color. In the case of white wine, pressing happens before the fermentation step as skin pigments are not required for color.
4. Malolactic Fermentation (optional): Winemakers may choose to create conditions that encourage certain bacteria to convert malic acids into lactic acids to soften the taste of the wine. This process is a common part of red wine production, but it is less common for white wine production. (Note: Chardonnay is an exception; it frequently undergoes malolactic fermentation which produces the compound that gives it a “buttery” flavor.)
5. Lees Contact/Stirring (optional; only applies to white wine production): In the case of white wine production, after fermentation has stopped, winemakers may choose to let the wine rest in contact with the dead yeast cells for a period of time to add flavor and complexity. The wine is later separated from the lees.
6. Aging (optional): This step is only undertaken if the winemaker feels a wine will improve by aging before being released for sale—for example, if the winemaker feels aging will help soften and enhance the flavors. Oak casks/barrels are usually used when aging high quality wines; winemakers may also choose to use tanks or vats.
- Racking (occurs during Aging): As the wine matures, sediment forms and settles at the bottom of the container where it is aging. To prevent it from having an adverse impact on the wine’s flavor, the clear liquid is siphoned off into a new container where it can continue to mature. This process may take place several times.
- Fining (occurs during Aging): Sometimes an agent is introduced to the wine to remove minute solids still suspended in the liquid. The agent binds with the molecules and causes them to settle to the bottom of the container so that the clear wine can be separated from the sediment. This process also reduces excess tannin in the wine.
7. Blending and Bottling: Wine from different containers is blended together and allowed to settle in a tank. The wine might also be filtered. It is then bottled, and may spend more time aging in the winemaker’s cellar before it is released for sale.