How Wine Is Made: The Winemaking Process, from Grape to Bottle

From grape to must

Winemaking begins with the harvest, picking the grapes once they’ve ripened. The sources behind this Recap don’t go into the timing or methods of the harvest itself: from this point on, the grape becomes a raw material to be worked in the winery.

The next step is crushing: breaking open the grape berries. According to Treccani, splitting the skin and the cell membranes underneath speeds up the release of the juice and lets the solid and liquid parts mix, bringing the microorganisms that drive the transformation of must into direct contact with the liquid — the same exchange that happens inside every cell. Alongside crushing, or right after it, comes destemming, which separates the berries from the stems, the bunch’s woody part. Wineries often run both steps together, in a machine called a crusher-destemmer; some models use a spinning drum that throws the grapes against the walls, while others add a screw press that handles the pressing step too.

Alcoholic fermentation: yeast at work

Under the standard set by the OIV, the International Organisation of Vine and Wine, alcoholic fermentation is the conversion of grape sugars into ethanol, carbon dioxide and secondary products — literally the reaction that turns must into wine. It runs on the same mechanism that makes bread rise: yeast draws energy from sugar without using oxygen, leaving alcohol and gas behind as byproducts.

The OIV’s Code of Oenological Practices recognizes two routes. Fermentation can happen spontaneously, driven by the yeast already present on the grape skins, in the must and in the winery; or through inoculation, adding selected yeast strains to the must before or during the process. Among the accepted ways to encourage, slow down or stop fermentation, the Code also lists temperature control, chosen to suit the wine being made.

Real-world example: the moment must hits the tank, the yeast finds all the sugar it needs to multiply and starts fermenting it right away. The carbon dioxide produced rises to the surface as bubbles — which is why a fermenting tank seems to bubble on its own, with no flame under it.

Red or white: maceration makes the difference

A wine’s color isn’t determined by the grape alone. According to Treccani, red winemaking involves macerating the solid parts — skins and seeds — together with the must: the must sits in contact with these solids and picks up color and tannins from them. During maceration the skins tend to rise to the surface, forming a cap that needs to be managed so it stays submerged in the liquid.

Maceration is followed by racking, drawing the wine off the solid parts; the leftover skins and seeds are then pressed to recover the liquid they still hold.

In white winemaking, the juice separates from the skins almost immediately after crushing, with little or no maceration — which is why even grapes with dark skins can yield a pale wine.

Aging

After racking, according to Treccani, wine is stored in barrels, oak casks or stainless steel tanks for aging. Encyclopaedia Britannica describes what happens inside the wood: oxygen enters slowly through the staves, some water and alcohol evaporate, the wine’s acidity drops and compounds form that add to aroma and flavor. The process can run from a few months to several years, depending on the wine and the result the winemaker is after.

Stainless steel tanks work differently: sealed almost airtight, they let in far less oxygen and keep the fresh, fruit-driven aromas better preserved.

Bottling

Before bottling, according to Encyclopaedia Britannica, wine may go through blending, combining different wines to even out taste and quality, filtration, which removes solid residue left in suspension, and treatment with antiseptics, to keep unwanted microorganisms from developing before the bottle is finally sealed.

The legal definition of wine

Not everything made from fermented grapes can legally be called wine. Under an official OIV resolution, wine is exclusively the beverage resulting from the total or partial fermentation of fresh grapes, crushed or not, or of grape must. Its actual alcohol strength can’t fall below 8.5% vol; an allowance down to 7% vol applies for particular climates, terroirs, grape varieties or the traditions of certain vineyards, and on the label the stated value can differ from the real one within a tolerance of ±0.3% vol.