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Grapes-yeast fermentation
“ . . .. From the moment that they escape from the egg, one sees that these animals swallow sugar from the surrounding solution; one can see it arrive in the stomach quite clearly. It is instantly digested, and this digestion is instantly and most definitely recognized by the subsequent expulsion of excrement. In a word, these infusoria eat sugar, empty wine alcohol from the intestinal canal, and carbonic acid from the bladder.”
— Friedrich Wöhler, 1839
Our species has been making wine and beer for about 5000 years. We didn’t know what we were doing until the 1800s.
We knew the fermentation of wine and beer depended on where it was from. That every region had its characteristic yeasts, which infected the juice of its grapes and the wort of its grains spontaneously. And that’s about all we knew.
Then, in the 1830s, a cell theory of fermentation began emerging. One of Europe’s great organic chemists, Friedrich Wöhler, anonymously reported that he had seen “wine animals” through his microscope. By the middle of the century, Louis Pasteur dispatched the chemical theories of fermentation and invented the science of microbiology.
Winemaking can be divided into three stages. In the first, ripe grapes are crushed into juice. In the second, the grape juice is fermented by what Wöhler called wine animals. What we call yeasts. Yeasts metabolize sugar and produce carbon dioxide, alcohol, and energy. Yeasts also strongly affect the aromas and flavors of wine by producing molecules that the grape cannot supply. The kinds of yeasts, the temperature at which fermentation occurs, and the length of time the juice is left in contact with the grape skins all affect the aromas and flavors of the wine. The third stage of winemaking is called the aging, development, or maturing of the fermented juice. The chemical constituents of the grape and the products of fermentation react with each other and with oxygen to form a stable system with attractive aromas, flavors, and body. This development may take place in large stainless steel tanks, large or small oak barrels, or in the bottle.
More Sugar, More Alcohol
Yeasts are a group of about 160 species of single-celled microscopic fungi. Most of the yeasts which make wine, as well as beer and bread, are members of the genus called Saccharomyces, or “sugar fungi.” The important yeasts for winemaking are strains of Saccharomyces cerevisiae called ellipsoideus for their shape. These fungi breed, grow, and live naturally on the skins of their grapes, as well as all around their winery. Over 100 different strains of several native yeast species can thrive on the skins or in the juice of their grapes. These native wild yeasts — wine animals native to their grapes and their earth — are ideal for fermenting the juice of their grapes into wine.
The greater the sugar in the grapes the yeasts ferment, the greater the alcohol in the wine. But high degrees of alcohol are toxic to yeasts. Wine ceases fermenting at about 15% alcohol, even if it has unfermented sugar. High degrees of sugar are also toxic to yeasts. Sweet wines cease fermenting at low percentages of alcohol. Any unfermented sugar in the wine is called residual sugar. Even dry wines may have a small quantity of sugar that can’t be fermented, but which may not be detected on the palate. When the yeasts die at the end of fermentation, they sink to the bottom of the fermentation vessel and form a sediment called lees. White wines may be left on their lees while aging, which can impart extra body and character to the wine.
Since the middle of the 1900s, a vast majority of winemakers has been using sulfur dioxide to kill off the wild yeasts native to their grapes. These winemakers then add yeasts cultivated in a factory to the juice of their grapes. Factory yeasts license winemakers to manipulate the aromas and flavors of their wine. They license winemakers to manage fermentation as if their wine were a widget in a factory. They license winemakers to kill the vitality of their wine.
If you buy wine in a shop or order wine at a restaurant, ask for wine which was fermented spontaneously with its wild and native yeasts. You’ll be asking for living wine. A wine made by its very own wild and native animals.
