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Given that supermarket shelves groan under the weight of so many varieties — wine, fruit, rice, wheat — you might wonder, what can and can’t be turned into a vinegar?

Any fruit, juice or grain that contains sugars can undergo yeast fermentation to produce an alcohol. This alcohol undergoes another round of fermentation to make vinegar. Hence the wide variety of base materials you see on the vinegar shelves.

The word “vinegar” comes from the French vin aigre, or sour wine. The “sour wine”, ancient humans discovered, can help preserve almost anything (meats, sauces, produce) for extended periods. Here’s why: Alcohol is itself a fairly hostile environment for microbial growth. There is one genus of bacteria, the Acetobacter, that can extract energy even from alcohol. Once it’s done, the resulting acidic liquid is inhospitable to almost all life forms, which makes it a most effective food-grade preservative.

Vinegar is basically the ethanol in alcohol broken down into acetic acid (4% to 6% concentration), water and flavours that were unique to the starting material. (CH3CH2OH (Ethanol) + O2 (Oxygen) + Acetobacter = CH3COOH (Acetic Acid) + H2O (Water) + Flavour).

But humans didn’t need to wait until they understood the chemistry to make it. As early as 4000 BCE, the Babylonians were making vinegar from dates and raisins, and using it to pickle foods. By the Christian Era, it was being mixed in water to create a drink called posca, popular among Roman soldiers. During the Zhou dynasty (1046-256 BCE), the Chinese appointed specialised vinegar-makers to make dark vinegars from rice and wheat.

The ancient methods of producing vinegar didn’t involve actively adding Acetobacter. Wooden barrels were just partially filled with alcohols and allowed to sit, for anywhere between two months and several years. Since the barrels weren’t airtight, and since Acetobacter is present in a large number of the raw materials used to make alcohols, the process would begin of its own accord.

It was in the 17th century that the French began to speed things up. They used a “trickling” method in which the alcohol was poured over wood shavings and other porous materials, to increase exposure to oxygen. This shrunk the production cycle from months or years to a few days.

The modern process of “submerged fermentation” used widely today was developed in 1949. Here, air carrying Acetobacter culture is pumped into large tanks of alcohol, turning it into vinegar in 24 hours. Most vinegar in stores today is clear and transparent because it is further filtered and pasteurised, to remove the Acetobacter.

Vinegar, in this form, has an almost indefinite shelf life, because of its high levels of acidity and lack of microorganisms in the bottle. These days, raw, unpasteurised vinegar “with the mother” is also popular. The mother is simply a layer of cellulose formed by Acetobacter during fermentation. While the health benefits have not been fully studied or verified, raw vinegar with mother can act as a starter culture for a fresh batch.

So what is it that you’re seeing on the shelves? The simplest kind of food-grade vinegar available today is distilled white vinegar, which is industrially manufactured from distilled alcohols. It is colourless, has a sharp acidic taste and little else in terms of flavour. It is best used in dressings, sauces and emulsions such as mayonnaise. It is inexpensive.

In the mid-range are supermarket vinegars made from cider, fruit, malt, rice, etc. They come in a range of colours, flavours and fragrances, with slight variations in acidity levels.

The most expensive vinegars are aged vinegars such as balsamic vinegar (made from Modena wine, originally in Italy) and sherry vinegar (made from sherry, originally in Spain). Traditional Balsamic Vinegar PDO (Protected Designation of Origin, under European Union norms) is aged for 12 or more years. Sherry vinegar is aged for two to 10 years. Both are still traditionally matured in wooden barrels.

This is important because, over time, vinegar gets thicker from evaporation and develops flavour notes from concentration, microbial activity and extended contact with wood.

Unfortunately, manufacturers are allowed to use the term “Balsamic Vinegar of Modena” even if they are not using the traditional method. Check the ingredients label. If it lists wine vinegar, sugar and caramel colouring, then the vinegar has been industrially processed. While there’s nothing wrong with that per se, you might want to check the price again, now that you know.

To reach Swetha Sivakumar with questions or feedback, email upgrademyfood@gmail.com

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