Vinegar fermentation is carried out by acetic acid bacteria, primarily Acetobacter species. These bacteria consume ethanol (alcohol) and oxygen, producing acetic acid (vinegar) and water. This is why vinegar making requires an alcoholic base and exposure to air - both are essential substrates for the bacteria.

The "mother" is a mat of cellulose produced by Acetobacter. It looks like a SCOBY but serves a different purpose - it's a biofilm that concentrates bacteria at the liquid-air interface where oxygen is most available. The mother isn't necessary for vinegar making but speeds the process significantly.

Commercial vinegar is typically 5-6% acetic acid. Homemade vinegar usually reaches 4-7% depending on starting alcohol content. Vinegar's high acidity (pH 2.5-3.5) makes it self-preserving - harmful bacteria cannot grow in this acidic environment.

Unlike most ferments, vinegar making is aerobic - it requires oxygen. Acetobacter use oxygen to oxidize ethanol into acetic acid. This is why vinegar vessels must never be sealed and benefit from wide openings that maximize surface area exposure to air.