shelf life chemistry
Bill Tindall, E.Tn.
The stuff is a protein and relies on the length of the protein molecule to be strong. The molecules have to be long (and hence entangled) to pull "strings" but Titebond does not think this test is best.
Other glue is liquefied by addition of urea. Urea decomposes to ammonia. Ammonia chops up the protein. If the bottle stinks of ammonia be cautious using it. Bacteria chop up the protein. If it smells rotten chuck it.
Titebond liquefies with a chemical that does not decompose or in any way cause the molecular weight of the protein to shorten. Other factors can/will slowly degrade the protein so the stuff does not have an infinite life. Stored in frig and it will last a long time.
It is cheap and readily available. Buy a new bottle every few years or learn how to test the joint for glue strength, or the glue itself for effective strength to ensure gluing success.