Winemaking begins with the collection and crushing of grapes. For white wines
the grape juice is separated away from the skins and clarified via cold settling,
filtration or centrifugation. The juice is then moved to a barrel or fermentation tank
and the alcoholic fermentation is carried out by yeasts indigenous to the juice, or
via inoculation of a selected S. cerevisiae starter culture. White wine fermentations
are typically carried out for roughly one to two weeks at temperatures around 10 to
18 °C. Upon consumption of available glucose and fructose, the main sugars in
grape juice, the wine is considered “dry” and separated from the yeast and grape
lees (sediment).
Red wines are produced slightly differently than white wines. After crushing the
skins are left in the fermentation to allow for color extraction. Like white wines, the
alcoholic fermentation commences either through the action of indigenous yeasts
or via direct inoculation of a starter culture. During the fermentation the grape
material tends to float to the top of the vat forming a “cap.” To better enable extraction of red pigments and to influence wine flavor, winemakers typically punch
down the cap or pump juice from the bottom over the cap. After a suitable period
of time, the wine is separated from the grape skins and the fermentation is completed in another vessel. As described for white wines, the red wine is now “dry”
and devoid of the main juice sugars.
After the alcoholic fermentation, wines often are spontaneously, or purposely,
taken through a malolactic fermentation in which the high level of malate in the
juice is converted to lactate, mostly by indigenous or inoculated LAB. Unlike the
alcoholic fermentation, the malolactic fermentation is a stylistic consideration by
the winemaker, who, through use of antimicrobial additions (primarily sulfur
dioxide) or filtration may choose to prevent this fermentation from initiating.
Once the wine has been taken through the alcoholic and, if desired, the malolactic
fermentation, the wine is often stored in tanks or barrels to allow flavor development. The residence time for storage is primarily determined by the style of wine
and winemaker choice. Often white wines are not stored for long periods of time
while reds are frequently stored in oak barrels for several years. While the average
wine contains approximately 13 percent ethanol, the alcohol by itself does not
preclude future spoilage. Consequently winemakers must take great care to prevent exposure of the wine to oxygen, which can encourage microbial growth,
as well as judiciously use antimicrobials (again, primarily sulfur dioxide) to prevent microbial spoilage.
Winemaking begins with the collection and crushing of grapes. For white winesthe grape juice is separated away from the skins and clarified via cold settling,filtration or centrifugation. The juice is then moved to a barrel or fermentation tankand the alcoholic fermentation is carried out by yeasts indigenous to the juice, orvia inoculation of a selected S. cerevisiae starter culture. White wine fermentationsare typically carried out for roughly one to two weeks at temperatures around 10 to18 °C. Upon consumption of available glucose and fructose, the main sugars ingrape juice, the wine is considered “dry” and separated from the yeast and grapelees (sediment).Red wines are produced slightly differently than white wines. After crushing theskins are left in the fermentation to allow for color extraction. Like white wines, thealcoholic fermentation commences either through the action of indigenous yeastsor via direct inoculation of a starter culture. During the fermentation the grapematerial tends to float to the top of the vat forming a “cap.” To better enable extraction of red pigments and to influence wine flavor, winemakers typically punchdown the cap or pump juice from the bottom over the cap. After a suitable periodof time, the wine is separated from the grape skins and the fermentation is completed in another vessel. As described for white wines, the red wine is now “dry”and devoid of the main juice sugars.After the alcoholic fermentation, wines often are spontaneously, or purposely,taken through a malolactic fermentation in which the high level of malate in thejuice is converted to lactate, mostly by indigenous or inoculated LAB. Unlike thealcoholic fermentation, the malolactic fermentation is a stylistic consideration bythe winemaker, who, through use of antimicrobial additions (primarily sulfurdioxide) or filtration may choose to prevent this fermentation from initiating.Once the wine has been taken through the alcoholic and, if desired, the malolacticfermentation, the wine is often stored in tanks or barrels to allow flavor development. The residence time for storage is primarily determined by the style of wineand winemaker choice. Often white wines are not stored for long periods of timewhile reds are frequently stored in oak barrels for several years. While the averagewine contains approximately 13 percent ethanol, the alcohol by itself does notpreclude future spoilage. Consequently winemakers must take great care to prevent exposure of the wine to oxygen, which can encourage microbial growth,as well as judiciously use antimicrobials (again, primarily sulfur dioxide) to prevent microbial spoilage.
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