Copyright 1997 Alan T. Hagan. All rights reserved.
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There is vinegar and then there is vinegar and it is not all alike. The active ingredient in all vinegars is acetic acid, but what the sour stuff is made from can vary widely. The most common vinegar is the white distilled variety which is actually just diluted distilled acetic acid and not true vinegar at all. It keeps pretty much indefinitely if tightly sealed in a plastic or glass bottle with a plastic cap. The enamel coated metal caps always seem to get eaten by the acid over time. It is usually about 5-6% acetic acid and for pickling it is the type most often called for.
The next most common variety is apple cider vinegar. There are two kinds of this type. A "cider flavored" distilled acetic acid type and a true cider vinegar fermented from hard cider. Either will store indefinitely at room temperature until a sediment begins to appear on the bottom. Stored vinegar will sometimes develop a cloudy substance. This is called a "mother of vinegar" and it is harmless. As long as the liquid does not begin to smell foul it can be filtered out through cheesecloth or a coffee filter and rebottled in a clean container. The mother can even be used to make more vinegar. If it begins to smell bad, however, it's gone over and should be tossed out.
The more exotic wine vinegars, balsalmic and other types all can be stored like cider vinegar. Age and exposure to light and air, however, eventually begin to take their toll on their delicate flavors. Tightly capped in a cool, dark cabinet or refrigerator is best for their storage.
DISCLAIMER: Safe and effective food storage requires attention to detail and proper equipment and ingredients. The author makes no warranties and assumes no responsibility for errors or omissions in the text, or damages resulting from the use or misuse of information contained herein. Placement of or access to this work on this or any other site does not mean the author espouses or adopts any political, philosophical or meta-physical concepts that may also be expressed wherever this work appears.