A foolproof [if that concept is possible] method of testing the freshness of liquid hide glue, that works every time.
Simply put a bead of liquid hide glue on a piece of porous paper and place the paper in a warm oven [150 to 200 degrees [F]] for 15 to 20 minutes, then remove and allow to cool.
When you bend the paper the bead of glue will break if the glue is fresh. If the liquid hide glue is not fresh it will bend without breaking.
The samples are from left to right liquid Fish Glue, fresh Franklin/Titebond liquid hide glue and finally Franklin/Titebond Liquid Hide Glue that is over 5 years old [two years spent outdoors year round] and the results show the cracking in the two fresh samples and wrinkles and flexibility in the old sample.
An excellent test, the two fresh glues also passed the legging, cottoning, or stringing test, the old glue did not.