Vinegar is created by two biological processes involving yeast and Acetobacter bacteria. Yeast changes sugar to alcohol and then the bacteria convert the alcohol into acetic acid. Vinegar contains many vitamins and minerals that acetic acid alone does not. Malt vinegar is made from the fermentation of barley malt or other cereals. Malt is created by allowing grain to steep in water and germinate. Enzymes then digest the starch and convert it into sugars before fermentation.
Homemade malt vinegar may be made from alcoholic beverages such as beer or ale, writes Donal O'Brien of the Barony of Dreiburgen, a community dedicated to 17th century practices.
Mix 3 parts preservative-free ale, beer or lager with 1 part water in the wide-mouthed container. The alcoholic beverage should contain 5 to 7 percent alcohol. Dilute higher alcohol content with water free of chlorine or heavy minerals. Cover the container with paper toweling or cheesecloth and set it aside in a dark area at room temperature for 24 hours.
Add Acetobacter bacteria to the alcohol mixture and replace the cover. You can add a small amount of active homemade malt vinegar or a piece of vinegar mother to your base or you can expose the mixture to the air. Home-brewing suppliers offer mother as vinegar starters. After a few days, a gray, leathery film will develop on the top, a sign that the mother is beginning to form.
Leave the mixture to ferment for at least one week. Very low or very high temperatures can slow the process. Temperatures between 70 and 90 degrees Fahrenheit are ideal. The homemade malt vinegar can be left to age as long as you like. Taste it after a few weeks to test its acidity and strength. The bacteria will stop working once all of the alcohol has been converted to acetic acid.
Strain the vinegar through coffee filters into bottles and place in the refrigerator. Pasteurize your malt vinegar by placing the bottles in a pot of water and bringing the pot to a boil. Turn the heat down gradually until the water is simmering, and then remove and cap the bottles. The vinegar must reach a temperature between 140 and 160 degrees and stay heated for 30 minutes. Pasteurized malt vinegar can be kept at room temperature.