Vinegars have very long shelf lives. Here are some things to consider before replacing old bottles.
Don't toss old vinegar. Most vinegars contain about 5 percent acetic acid, which (along with pasteurization) prevents the growth of harmful bacteria, and will last indefinitely.
Do ignore any sediment in your vinegar. The sediment is a harmless cellulose that our testing has shown doesn't affect taste; it can be easily strained out.