How wine is made
October 19, 2006
In recent weeks I have written about how the vintner checks the ripeness of grapes (sugar content), and about the harvest activities in all the growing regions of California. But what does the wine maker do to turn those freshly harvested grapes into your favorite bottle of wine? All grape varieties go through similar production steps during wine making to become fermented grape juice, which is what wine is.
Grape juice from both red and white grapes is, with few exceptions, always clear. What makes a wine red is the contact that the juice has with the grape skins. Those skins leach their color into the clear juice creating red wine. White wine is produced by removing the skins immediately limiting contact with the juice. In addition to adding color, the grape skins contain tannins, which give red wines that dry feel in your mouth.
The red wine grapes are either put in a crusher or a crusher-destemmer, depending on the varietal. Cabernet sauvignon is a naturally tannic grape while pinot noir is not. The wine-maker must decide to ferment with or without the seeds and stems.
When the seeds and stems remain during the fermentation stages they not only give the wine more structure from the tannins, but the color of that wine becomes darker. The crushed grapes form a mass of juice, pulp, skins, seeds, and in some cases, stems ” called a must. The must is placed in temperature-controlled stainless steel tanks to ferment.
Fermentation occurs when the sugars and yeast react producing alcohol and carbon dioxide (somtimes the wine maker inoculates the must with a manufactured yeast to produce specific flavors and other characteristics). The carbon dioxide dissipates into the air, bubbling up from the fermenting must, pushing grape skins to the surface to create a cap of skins. The wine maker gently pushes this grape cap back into the batch because the skins not only add tannins but give the wine certain flavors and aromas as well. Some wine makers will pump wine from the bottom of the vat and spray this over this cap.
During fermentation, the temperature of the must rises between 60 to 85 degrees from the chemical reactions between the sugars, yeasts and carbon dioxide. The fermentation continues until the yeast converts enough sugars into enough alcohol to kill off the yeast, usually around 15 percent. This process can take anywhere from a few days to a few weeks.
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After fermentation, the wine is drained from the skins. This “free run” wine is pumped or drained into barrels, or sometimes another tank, to begin aging. Many premium wines are made solely from this “free run” juice.
The remaining must in the vat is gently pressed to remove the remaining wine. This “first press” is highly concentrated and adds lots of flavors and aromas to the free run juice. At this point, after a short aging period, the serious red wines ” those that will be aged in the barrel and the bottle to be enjoyed some years down the line ” are placed in oak barrels for anywhere from a few months to years. Maloactic fermentation occurs during barrel aging for both red and some white wines, turning tart malic acids into softer lactic acids.
The very drinkable good reds that are not aged in oak for long periods of time are then bottled, after filtering or fining of the juice. This process is done to remove from the wine any particulate matter that may cause excessive tannins, and creates a more balanced wine.
In filtering, the juice is run through a series of filters on the way to the bottle.
Fining occurs when an agent such as egg whites, bentonite clay, casein, or some form of gelatin is stirred into the wine. These fining agents adhere to the particulate matter and fall to the bottom of the barrel. The clear wine is drawn from the top of the barrel.
Oak aging imparts certain flavors, aromas, textures, and complexity from the interaction of the wine with the wood.
Growers try to handle white wine grapes gently so that the grapes do not get crushed in transport from the vineyard to the winery. The contact between the juice and skin can cause tannins, affecting their normally delicate flavors and aromas. At the winery the juice is separated from the skins by gently pressing the grapes through a screen or by using a de-stemmer. The juice is pumped into a refrigerated settling tank, and the clean juice is then put into a fermenting tank.
White wine is fermented at between 50 and 65 degrees to help preserve the freshness of the fruit flavors. Some chardonnays are oak barrel fermented; more delicate whites do better with time in clean stainless tanks for fermentation and aging.
The oak fermented chardonnays develop toasty vanilla flavors fromthe oak. After fermentation the used up yeast cells called “lees” are drawn off the wine in the barrel. When a wine is said to have been left “sur lie”, that means that the spent yeast cells have not been removed, this adds more texture and complexity to the wine’s flavors and aromas.
White wines generally do not receive malolatic fermentation. The wine maker will either chill the wine, inject sulphur dioxide, or fine the wine to stop the malolatic fermentation. Chardonnays are the exceptions. The rich buttery flavors of chardonnay form during this fermentation stage.
White wines are cold stabilized to remove acid crystals, and some whites are oak barrel aged, while others are fined or filtered and bottled.
Janice Jones is a Truckee resident and wine consultant. Reach her at firstname.lastname@example.org.