I spoke with the folks at Fleishmann's today and this is what I gleaned.
Heat kills yeast , not cold.
The problem with freezing yeast is water. It creates water crystals that either rupture or spear the yeast cells, killing them.
"fresh yeast"has such a high % or free water freezing is death.
I told them I freeze yeast all the time, in a bag with air sucked out in a sturdy sealed container, they said, (unofficially) if you evacute the bag put in the freezer that is great, but if I suck the air out of a container then fridge it, it keeps way longer then is marked, for many years, although I am sure comapny policy is , if expired , we aren't responsible.
they also said if I had a vacumn device and I pulled a real vacumn on the jar it in and kep it in dark at 70 years it would last as long as in the fridge.
They also said Instant and Rapid rise are same thing and there is almost no difference from them and active yeast.
And that there is no big difference from any of the dried yeast as far as cell count of live or viable cells fer ml are concerned.
I will now make my self a jar sealer for vacumning the stuff in mason jars, and anyone who does, realize this IS NOT the same as boil vacumn sealing food. By pulling 29 inches of atmospere out we remove all the moisture. That plus heat degrade the yeasties, our buddies.
this IS the tastiest spot on the web!