Thing is, vinegar is produced by bacteria that only eat alcohol and alcohol is mainly produced by microbes that only eat sugar.
This is correct. The process you want to stimulate is first an alcoholic yeast based fermentation followed by an acetobacter fermentation to produce vinegar. Acetobacters need both alcohol and oxygen to produce vinegar. But too much alcohol is a problem. Acetobacters really don't work well above 10% alcohol and do better in the 5% range. Any fruit must that has a sugar content giving a specific gravity of around 1.040 to 1.050 should work well. Pressed apple juice usually falls in this range as well.
You can either rely on a wild yeast fermentation or simply pinch a little bread yeast into the must. Let the must ferment and produce alcohol (about 5 days). When the alcohol fermentation really slows down or stops, add a little vinegar mother to the must and give it a stir. At this point it needs oxygen so the acetobacters can produce vinegar. Oxygenate (stir it up) every few days. Vinegarization should start in a few days but can take as long as 30 days to really complete. Start tasting the vinegar every few days after the first week or two to gauge its strength.
Note that adding other natural sugars to the cider must can generate great flavors. Wild blackberries are one of my favorites but any virtually any fruit will work. Also make sure that the must is fairly acidic before you start the alcohol fermentation. A PH of 3.5 to 4.5 is best. Pressed apple juice naturally falls in this range (hence the reason for so many apple cider vinegars). But if the must is not acidic enough, a tablespoon or two of lemon juice will generally correct the problem.
Vinegar is one of the easiest things to make in the kitchen. It really just makes itself as soon as you give it the right environment. it's also really addictive. Have fun with it.
