Old yeast question.

I recently bought 4 yweast Activator packs on clearance at LHBS, paid $1 per pack. All are 6 to 10 months past the manufactures date. Has anyone had success using yeast past the exp date? How long will the yeast remain viable if stored cold? Thanks for the help.

I've used plenty of White Labs and Wyeast yeasts that were will beyond the recommended date, with no problems. I've also used harvested yeast that was about 1 year old (home harvested yeast degrades much faster than the commercial samples), and yeast from naturally conditioned commercial beers that were well over 1 year old.
The old yeast will have a very low viable cell count. I make a very small starter (about 1/2 pint) to wake the yeasts up, and get them to start multiplying. After about 3 days (possibly up to a week if you don't use a stir plate), I step up the starter to the required volume, wait another day or two (perhaps 3 - 4 days without a stir plate), and then pitch.

-a.

They will last as long, as your will to make a starter for them. Most sealed packages Wyeast Packages will start to swell when they get old. You can always pop the package and see if it swells up. If it does, it's good to make a starter like above. I probably wouldn't start with a small starter like above. There is always going to be a significant number of of yeast cells, because live ones will eat the dead ones. As a matter of fact Biotin the yeast energizer is just dead yeast cells.