You probably already grasp the basic concept of wine making—throw some grapes into a tank, let them ferment, and voila! But, you might also like to know a little more about the nuts and bolts of the process, without getting too geeky of course. So, let’s do that.
The fermentation process happens through a number of steps, all of which I’ll list here in brevity. Think of this as your crib sheet to carry along on your next winery visit.
- HARVESTING—the first step is to bring in the grapes from the vineyard. Sometimes they’re picked by hand, put into small hand-carried bins, and transferred to larger 1-ton bins, which are pulled by a tractor to the winery.
PROCESSING—the grape bins are lifted by palate jack and dumped into a hopper on top of a crusher-destemmer. This gently separates the grape berries from the stems.
- (Alternatively, some percentage of the grape clusters are left intact, to ferment together.)
- After destemming, the berries are sent down a moving conveyor where people sort them to remove undesirable fruit and MOGs (material other than grapes) before they descend into a pre-washed 1-ton bin.
- JUICING—the fruit is then:
- Left in the individual bins to ferment; or
- The bin is dumped into a larger vat or tank to ferment; or
- The bin is dumped into a grape press to squeeze or gently coax the juice from the berries. This is then transferred to a larger vat or tank to ferment separately, as it contains more tannins.
- The initial juice collected before the press is activated is known as “free-run.”
FERMENTING—the grapes may have come into the winery with native (natural) yeast on the skins.
- If not—and sometimes even if—a commercial yeast is then added to the must (unfermented grape skins and juice) to start fermentation.
- Fermentation may take place in a temperature-controlled large tank or vat, or 1- or 2-ton bin, or even a barrel. (If a bin or barrel is used, temperature control is maintained by placing it in a cold room, or a cooler part of the winery.)
- During fermentation, the cap (the grape skins and pulp that have risen to the top) is either punched down or pumped over with some sort of regularity. This imparts color and flavor. (Interestingly, nearly all red grapes have white pulp. Thus, it’s actually the skins that give red wine its color.)
- The yeast feeds on the sugar, converting it to alcohol while giving off carbon dioxide and leaving you with wine.
MORE FERMENTING—shortly after initial fermentation (5-30 days depending on winemaker choice) nearly all red wine and some white wines go through a second fermentation.
- This may happen naturally or be induced. The purpose is to convert the more acidic malic acid (like green apples) into the softer lactic acid (like milk). This is referred to as malolactic fermentation, or ML.
- This may take place either before or after the wine goes into barrel.
TANK OR BARREL—Many white wines do not go into barrel, but rather into a large stainless steel tank. Red wines normally go directly into barrel for an aging period that lasts from months to years, depending on preference.
- Stainless steel tanks impart nothing extra to the wine. With white wines, this leaves a purity of fruit.
- Oak barrels impart aromas and flavors, and they round out the tannins in red wines.
- A process called racking is done with some regularity (though not always—again, according to winemaker preference). It consists of moving the wine through hoses from one vessel to another. Its purpose is oxygenation and separation of solids.
So, there you have a concise look the wine-making process.