Yeast IS hardier than most newish brewers wanna give them props for...I mean You can't say that THIS YEAST was stored "properly" and yet, they managed to make a batch of beer with it.
45 million year old yeast ferments amber ale
If we can make beer with that....
Yeast are really tenacious critters, except in the rarest and most extreme circumstances, they will survive, reproduce and work for you. If they can harvest 4500 year old yeast from a hunk of amber, then even and outdated packet of dry, a deflated smack pack, or properly stored outdated tube, will more than likely still have enough viable cells to reproduce into a starter.
Bobby M recently did a test on year old store yeast here; http://www.homebrewtalk.com/f13/test...bility-126707/
And my LHBS cells outdated tubes and packs of yeast dirt cheap 2-3 dollars each
and I usually grab a couple tubes of belgian or other interesting yeast when I am there and shove it in my fridge. and I have never had a problem with one of those tubes.
I usually make a starter but I once pitched a year old tube of Belgian High Gravity yeast directly into a 2.5 gallon batch of a Belgian Dark Strong, and after about 4 days it took off beautifully.
I don't know if you know the story of Charlie Papazian's yeast (White Labs "Cry Havoc") or not. He talked about it on basic brewing. The recipes in both Papazian's books, The Complete Joy of Homebrewing and The Homebrewers Companion, were originally developed and brewed with this yeast. Papazian had "Cry Havoc" in his yeast stable since 1983
He has used it nearly continuously since 83, sometimes pitching multiple batches on top of a cake, sometimes washing or not washing, etc. In a basic brewing podcast iirc last year he talked about how a batch of the yeast after a lot of uses picked up a wild mutation, and he noticed an off flavor in a couple batches.
Now most of us would prolly dump that yeast. Instead he washed it, slanted or jarred it (I can't recall which,)marked it, and cold stored it, and pretty much forgot about it for 10-15 years. He had plenty other slants of the yeast strain, so he left it alone.
Well evidently he came across that container of yeast, and for sh!ts and giggles made a beer with it. Evidently after all those years in storage, the wild or mutated yeast died out leaving behind a few viable cells of the "pure" culture, which he grew back into a pretty hardy strain...which iirc is the culture that White Labs actually used for their cry havoc...because of it's tenacity and survivability.
It really to me, just goes to show once again how really hard it is to f up this beermaking, and that to give the yeast the props they deserve.
If you stock up and keep it cold you'll be fine...with dry since you don't make starters with it, make sure to proof/rehydrate it first, and the older it gets (2-3 years past expiry date) you might want to pitch TWO packets instead of one, but since it is so cheap it won't matter.