Vinegar production requires three separate fermentation steps.
Fermentation takes place when yeast ‘eats’ sugars and turn the sugars into alcohol. This is the process by which grape juice becomes wine, apple juice becomes cider and malted barley becomes beer. While it is all the same process the type and quality of the raw material being fermented determines the quality of the wine/cider being produced.
Next, we introduce a bacteria called Aceterbacter. This bacteria ‘eats’ alcohol and produces Acetic acid. This is the process by which wine becomes Wine vinegar, apple cider becomes apple cider vinegar and beer becomes malt vinegar. The bacteria needs oxygen and produces heat as part of this process.
After acetic fermentation the vinegar is settled, possibly filtered, blended and aged in oak barrels. It may be sweetened or not depending on the style being made.
Lastly, after oak aging for several months or perhaps many years the vinegar is removed from the oak barrels, possibly blended, usually filtered and then bottled.