I bought a one pound pkg of Fleischman IDY in Feb 2011 (best before Feb 2014), opened it, filled an old, clean empty 113g Fleischman jar and placed it in the fridge. The remainder of the one pound package sealed tightly with two elastics and placed in the freezer. Refilled jar as required, everything was fine. I had been doing this for at least five years.
In January 2013, my pizzas began to have off flavors. Dough rose as normal but the nice flavors in the crust were gone. Went to the Fleischman website and followed their instruction, mixing 1/4 c warm water with 1 tsp sugar, yeast and allowed to double in 10 minutes. Yeast doubled as per requirement.
I posted my problem on Freezing Yeast thread and Chicago Bob suggested I buy a single packet and try that. I did and the crust was back, the flavors had returned. Somehow the yeast had gone off?
As I reflected on the situation, after water, yeast is the cheapest ingredient in the process. I have decided that I will now buy a new 113g jar, every four months. For me, my pizzas are just too important.
When researching the problem, a woman on one of the sites I visited said she had bought four pounds of IDY from a bakery going bankrupt in 2003 and the yeast was still great today. I am glad I tried the packet and saw the difference.
All The Best