Whilst cyder is a yeast fermentation of sugar to alcohol, vinegar is produced by the bacterial fermentation of alcohol to acetic acid.
Vinification is a naturally occurring process; we have all experienced a bottle of wine going “vinegary” in the kitchen, indeed, there are many people who produce their own vinegar by such methods. However, in most cases, the natural vinegar forming bacteria – acetobacter – don’t convert all the alcohol to acetic acid, and the two then chemically react with one another to form ethyl acetate. Think of the aroma of nail polish remover or Airfix glue. A key factor in the fermentation of great vinegar is therefore ensuring all of the alcohol is converted to acetic acid, and in order to do this it is necessary to have an acetifier. Essentially, this is a large tank or tower; it is temperature controlled – acetobacter have a tendency to get a little over excited during a fermentation, and such is their frenzy they can overheat and die. They also need a ready supply of oxygen pumped through the tank to keep fermenting, and this is pumped in as tiny bubbles.