lunedì 4 marzo 2013
Crash course in homemade vinegar
From the sun to the grape
It begins with the miraculous process of photosynthesis. The sun creates sugar inside fruits and vegetables. The stronger the sun (e.g., in Sicily), the higher the quantity of sugar. (That's why Sicilian wines are so strong.)
From the grape to wine
For millennia, people thought that fermentation occurred when sugar decomposed. Pasteur was the first person to say that sugar does not decompose; there is a second element involved: yeast.
Under the right climatic conditions, "good" bacteria and fungi live — which is the reason why all the people in Alto Adige make Speck in their basment, and no one dies. It's also the reason that our ancestors drank wine without dying. Yeast already lives on the skins of grapes. (Nowadays, one washes the grapes well, and the winemaker adds a yeast that he or she trusts.
The yeast unites with the sugar. (This sugar has a dirty name: carbohydrates!) This union between the yeast and the carbs produces two things: carbon dioxide and ethanol (the drinkable alcohol). Voilà, fermentation!
This is very interesting: In breakmaking, the CO2 makes the dough rise, and the alcohol evaporates in the oven. In winemaking, the result is the opposite: the alcohol remains, and the CO2 escapes. If instead you want to prevent the escape of the CO2 and keep it in the wine, you end up with ... sparkling wine! (Just imagine: a 750 mL bottle of champagne at 68ºF contains 49,000,000 bubbles!)
From wine to vinegar
We go to great pains to protect wine from oxygen. There is a very good reason for this.
Above I explained the miraculous chemical process of going from sugar and yeast to wine. To go from wine to vinegar is another miracle. In the air that we breath, there are already bacteria and fungi. You don't have to search for them — they find you! For example, mold: leave a fruit on the counter, and the mold finds it. It's the same thing with many "good" bacteria.
A genus of these bacteria is called Acetobacter. All of the species of Acetobacter have the capacity of transforming ethanol to acetic acid in the presence of oxygen. In other words: expose wine to air, and good bacteria turn the alcohol into vinegar.
To make homemade vinegar is very simple.
When you open a bottle of wine and you drink most of it, but there's a little left over, pour the leftover wine into a bottle of wine vinegar of the same color. Keep doing that. Eventually, the wine will become vinegar.
But how long does it take? Depending on the ratio of vinegar and wine, it takes many months to obtain vinegar. How can one accelerate the process?
Oxygen, which in wine you didn't want, in vinegar you do want. You can keep the cap loose. You can eliminate the cap and cover the bottle with a piece of cheesecloth and an elastic. You can let in even more oxygen if you use a wide-mouthed container – either glass, stainless steel, or ceramic, but not plastic. Cover the opening with cheesecloth and an elastic, or with a thin dishtowel. (Obviously, the covering is to keep fruit flies away.) Put the container in a dark place (but not a cold one; warmth accelerates the process).
Adding more vinegar to the wine obviously accelerates the process.
You can accelerate the process considerably if you add a bacterial starter which is called "vinegar starter" or "mother of vinegar." This starter works in the same way as sourdough yeast: you combine the flour and water, wait a few days, the sourdough rises, then you save a little piece of it, which becomes the starter for the subsequent dough. You can continue this process for years, even decades. With vinegar the concept is the same (even if yeast is a fungus and vinegar starter is a bacteria).
If after some time you see the formation of a greyish or pinkish layer on top, that is normal. That layer is the "mother," the cellulose that the bacteria produce. As soon as all the alcohol changes into acetic acid, the bacteria will have completed their job. You can filter the vinegar with an unbleached coffee filter. But if instead you want to intentionally save the mother, you can use it as a starter for the next vinegar, continuing the process for many years.
Don't lose courage!
If all of this talk of bacteria and fungi is making you faint-hearted, fear not! You can simply add leftover wine to vinegar of the same color, and you're done. It will not be acidic enough for salad, but for cooking it will be excellent!