mother

I. The float

A vinegar mother is a biofilm. It looks like a wet brown disc, or a sheet of damp leather, sitting at the surface of an open jar of wine that’s been left somewhere warm. It is a colony of acetic acid bacteria — Acetobacter species, mostly — bound into a matrix of cellulose they secrete around themselves.

The bacteria are obligate aerobes. The cellulose matrix is buoyant. So the colony positions itself exactly at the interface between air and liquid: the only plane where its metabolism works at all. The disc is not a lid the colony has built over its food. It is the colony, standing on its food, breathing.

II. The conversion

Acetic acid bacteria eat ethanol and exhale acetic acid. The intermediate is acetaldehyde — the same molecule the liver makes when it processes alcohol and then has to push further to neutralize. The bacteria do the second step too, but they stop there. Vinegar is what gets stuck halfway through being something else.

A jar of wine left to a mother will sour at a few percent per week, depending on temperature, oxygen, surface area. The math is dull. The sentence is: the bacteria eat what got the grapes drunk, and the grapes wake up sober.

III. Inheritance

Once you have a mother you can keep her. Pour off the finished vinegar, top up with new wine, the colony adapts and goes back to work. Some kitchens have kept the same mother for decades, periodically subdivided to start jars for friends. The disc gets thicker year over year, layered like sediment, each new generation of cellulose laid down on top of the last.

If you don’t have one you can grow one. Start with raw unpasteurized vinegar — the cloudy kind, the kind with sediment — and add wine and air. A skin forms in a week or two, thickens into something you can pick up. It feels like a slice of rubbery liver. It will float in your palm.

IV. The end

When the alcohol is gone the bacteria starve. The mother sinks. Left in the jar a few months past the end of its food, it dissolves slowly back into the vinegar it produced, until the jar looks clear again and there is no evidence anything ever lived there except the smell.