The process of making wine begins, of course, with growing grapes and extracting their juice.  But then what happens?

I’m here to elucidate (which is not a word you want to try saying after you’ve drunk a little too much wine, by the way).

Once the juice is in the vat, it’s left to ferment. Traditionally this fermentation was brought about by natural yeasts present on the grape skins, but today cultured yeasts are often added. Yeast feeds on the sugar in the juice and converts it to alcohol. If the wine is left fermenting long enough, the yeast will eventually convert all the sugar into alcohol. The result is a “dry”–non-sweet–wine. However, fermentation can also be stopped at any point to produce a sweeter wine. (It took me years to figure out how a liquid could be “dry.” I still think it’s an odd choice of words.)

Wines are either white, red, or rose. The color of red wines comes from the skins of the grapes, which are left in contact with the wine during the fermentation process. As alcohol is produced, it leaches color from the skins. With white wines, the skins of the grapes are taken away before this happens.. With rose wines, the skins are left in contact with the fermenting line just long enough to create the desired shade.

Alcohol also leaches tannin from the skins. Tannin, as a result, is present only in red wines, and its astringency accounts for most of the difference in taste between red and white. As wine ages in the bottle, the tannin combines with the coloring and precipitates out as sediment. This is why a well-aged red wine is generally smoother than a young red wine.

By-products of fermentation include various chemicals–glycerol, esters, aldehydes and acids–all of which affect the quality of the finished product. This immensely complicated mixture of chemicals is what makes every batch of wine absolutely unique–and keeps wine connoisseurs fascinated.

Sparkling wines are produced one of two ways. In the traditional “champagne” method, cultured yeasts and sugar are added to a base wine, and a second fermentation takes place in the bottle. Another by-product of fermentation is carbon dioxide; dissolved in the bottled wine, it forms bubbles when the wine is opened. (Some cheaper sparkling wines are “fizzed” by artificially injected carbon dioxide into the wine under pressure, just as is done with soft drinks.)

Fortified wines, such as port and Madeira, are created by adding grape spirits to regular wine. This kills the yeasts, stopping fermentation and making the wine sweeter and stronger than ordinary wine.

Before bottling, vestigial impurities in the wine must be removed. Cheaper wines are sometimes “flash pasteurized,” briefly exposed to heat. This removes the impurities but also stops the wine from developing further; aging a flash-pasteurized wine won’t improve it at all. Better wines are passed through extremely fine filters, instead, and some will continue to develop new subtleties of flavor for years after they’ve been bottled.

Although we usually think of wine as being made out of grapes, you can make it out of just about any type of fruit. I visited Stoney Ridge Cellars in Winona, Ont., where the winemaker, Jim Warren, has created wines out of several fruits, including peach and apple. Fruit wines are more difficult, he said, because they have a higher acidity and there’s a lot more pulp to deal with. But the results can be delightful.

Warren has a reputation in the Ontario wine industry as an experimenter, always trying new techniques, so I asked him about the role of science in wine-making. Warren said that science certainly has played a large role in the development of winemaking and will continue to do so in the future. In the Niagara peninsula, for instance, sensitive environmental sensors are being installed in vineyards to record sunshine, rainfall, temperature and other factors that effect the vines’ growth. This information may help winemakers predict the characteristics of grapes harvested from various vineyards and choose which to use in their wines.

In general, any increase in knowledge is useful, Warren said, but he doesn’t believe winemaking will ever be a science in the sense that, say, computer-making is a science. Much of what he tries is based more on intuition and experience rather than scientific knowledge, and for that reason, he believes winemaking will always be more of an art than a science.

I suspect wine-drinkers wouldn’t have it any other way.

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