My wife bought me 2 ahs extract kits for xmas (bud american ale, and pumkin ale) and i haven't got to brewing yet. She was smart enough to hide the yeast in the fridge. How long will liquid yeast survive? I hope to brew on friday?
Liquid yeast last for 4 months from date of manufacture when properly stored. Date of sale is not the same as date of manufacture. The yeast packs will have a date printed on them.
BUT understand that the yeast loses viability during storage. So if it was 100% viable at manufacture you may only have 50% of those cells 2 months later. In any case make a starter any time your using liquid yeast.
Dry yeast is much more stable and lasts something like 2 years when properly stored. Dry packs also have a date on them. Same loss of viability during storage. It just much slower.
Actually, Wyeast has a 6 month guarantee, from their website: "The Activator™ package was designed with superior UV light- and oxygen-barrier material to extend shelf life, making our 6 month from manufacture date Product Warranty possible."
White labs states 4 months, from their website: "The shelf life for White Labs Yeast is four months. Yeast used after this point is usually fine, but lag times will be longer. There will be living yeast in most vials for 6-12 months, so if a starter is made to activate the yeast, successful fermentations can be carried out with aged yeast."
Both companies state that the yeast is fine after 6 months, but a starter should be made if using liquid yeast that old.