How long after purchase will jelly, jam, or preserves remain good to eat?

Unopened  jars will remain good for about a year.  The "best if used by" date on the product refers to the last date that the product will be at its peak quality.  That date is not about safety.  Note that some of these products have a "use by" date months past a year in the future.

However, the low-sugar varieties may lose color and texture more quickly because the sugar in the regular product acts as a preservative.

 For a discussion of the shelf life of open jars, click here:  http://shelflifeadvice.com/content/jelly-jam-and-preserves. 

Source(s):

University of Wisconsin "Jams, Jellies and Fruit Preserves"

National Center for Home Food Preservation "Jams and Jellies"