Wine 101: How grapes get turned into wine

Once grapes are picked from the vine, they enter a winery’s cellar. But what’s the magic behind the cellar doors that turns grapes into fine wine?

With my Wine 101 column I share what I know about wine to enrich your experience with it. Today I’ll explain how wine becomes wine, highlighting some of the key steps in the process.

Headed to the tanks: For both red and white grapes, they’re gathered in bins and brought to the crush pad. That’s where they’re sorted and then crushed. The stems are either removed or kept in the mix, depending on the preference of the winemaker.

The juice of all grapes — red and white — is almost colorless, with a few exceptions. But when the red grapes are crushed, the juice transported to a tank includes the skins of the grapes, as well as the seeds.

The skins are like a packet of dye. They contain tannin, which gives a wine backbone and structure. Tannin also acts like a natural preservative. The amount of tannin varies, depending on the varietal. For example, the skins of cabernet sauvignon contain more tannin than the skins of pinot noir.

As for the white grapes, they’re pressed and the skins are removed before the juice is put in the tank.

For both reds and whites, the liquid concoction — the juice of the crushed grapes, the seeds and possibly the skins — is called must.

The kick-start of yeasts: Yeasts convert grape sugar into alcohol, beginning the fermentation process. And there are two types of yeasts — ambient and cultured.

Ambient yeasts are sometimes called wild or native yeasts because they’re naturally present in the vineyard and in the winery. These yeasts are often preferred by winemakers who believe they add extra complexity to a wine.

Cultured yeasts, by contrast, are grown in a laboratory. Winemakers often choose them to maintain control over the fermentation process.

The fermentation process: Fermentation is a chemical reaction that emits carbon dioxide and heat as yeast converts grape sugar to alcohol. The temperature of the must rises to between 60 degrees and 85 degrees. Winemakers want to avoid temperatures rising higher than 85 degrees because they could burn off the delicate fruit flavors.

Oak barrel aging: Once the fermentation process is completed, wine is often put into oak barrels for aging. Oak has many complex chemical compounds that give nuance to aromas, flavors and textures in the wine. It gives the fermented juice intensity, depth and complexity. Oak also imparts notes of sweet vanilla, caramel, toffee, toast, tea and tobacco.

Fining: The process of fining clarifies a wine of solids floating in the liquid. To fine a wine, some sort of protein coagulant is stirred into the wine. Particles attach to the coagulant and fall to the bottom of the barrel. The clear wine is then poured into another vessel to separate it from the particles.

Into the cellar: Some may think that winemakers are resting after the harried harvest season. But most will tell you they’re still busier than ever with these steps of transforming grapes to wine.

You can reach Wine Writer Peg Melnik at 707-521-5310 or peg.melnik@pressdemocrat.com. On Twitter @pegmelnik.