“The star of oil and vinegar and the oil and vinegar of the stars”

The clever quote is attributed to the late Paul Newman, whose Newman's Own brand of salad dressing was a big hit. I often buy Newman's Own products, which still pump money into charities.

Things you might not know about a material that almost everyone has in the house:

• Vinegar consists of acetic acid diluted in water and heaven knows what else. The "what else" depends on the input materials — rice, corn, apples, etc. I'll explain.
• Vinegar is made from a traditional process by which bacteria convert ethanol to acetic acid.
• A vinegar-maker could purchase ethanol on the open market as feedstock, but usually the ethanol is made in-house using fermentation — the familiar process by which yeasts convert the sugars in rice, corn, apples, etc. to ethanol.
• Most vinegars have chemical carry-over from whatever sugary material was fermented to produce the ethanol. This is one reason why vinegars don't all look and taste the same.
• A small amount of ethanol (~1%) or sugar often remains in the vinegar.
• In the case of white or distilled vinegar, it's not the vinegar itself that is distilled. Rather, the ethanol was distilled so that flavor and color from the source of the sugar are left behind. The resultant product is very close to a pure solution of acetic acid in water.
• Many vinegars are filtered and pasteurized. Some are only filtered, and a few are sold "raw". Pasteurization removes compounds that contribute to taste and color. On the other hand, unpasteurized vinegar is likely to contain active bacteria — and if it also contains residual sugar or ethanol, you will find sludge in your vinegar after a while. You can remove the sludge with a paper coffee filter, if you choose.
• Growth of sludge in unpasteurized vinegar is retarded by refrigeration.
• Vinegar eels, a type of roundworm, thrive in dilute acetic acid. Harmless but visually disconcerting, they eat the sludge I described. Unfiltered vinegar may have them.
• Most pasteurized vinegars don't require refrigeration, but I know of at least one that recommends it. I suspect the colder temperatures preserve volatile chemicals that contribute to flavor.
• There is no governmental requirement that vinegar be labelled as pasteurized or unpasteurized.
• Some vinegars are treated after manufacture to change color or taste. Examples are tarragon vinegar, vinegars aged in wood (which, like whiskey, absorb organic chemicals from the wood itself), and ersatz "balsamic" vinegar. This is another reason why vinegars in supermarkets differ.
• Are some vinegars post-processed with added salt or sugar? Yes. Cooks beware.
• Can you make vinegar at home? Apparently you can, but it's so inexpensive that I don't know why you would.
• The concentration of acetic acid in most supermarket vinegar varies from 4 to 6%. Handle anything higher than 8% cautiously because undiluted acetic acid is so corrosive that it dissolves metal.
• Never pickle or can your own fruits and vegetables with less than 5% acetic acid. Dilute acid might not suppress hazardous bacteria.

What vinegars do you have in your house? At present we have five: rice, white wine, red wine, distilled, and "balsamic" (the affordable Modena substitute for the real thing). I use rice vinegar to brighten dishes; it is only 4% and has just a little flavor of its own without any added salt or sugar. Red wine vinegar is for cooking, white wine and balsamic for salad dressings, and distilled for cleaning.