How Old Is Old?

Somehow, I've ended up with two unused, past-dated vials of White Labs Yeast (WLP002 & WLP005), one dated may 2012, the other July.

Are they too old to use, or should I just go ahead and make a starter and see what happens?

They are getting a little old. However, I'd make a starter and use them if they're active. Anything over a year, I toss.

You never know until you try right. So long as there are some viable cells in there they will reproduce and should work.

At 6 months, they should be fine. They will have lost some viability, so will not be any good for straight pitching. Make a starter and they will be good to go. The starter will also confirm viability so you will not start worrying when you pitch them.

Mr. Malty predicts 10% viability at those ages. It's still a whole lot more yeast than guys get when they are culturing up the dregs from a bottle! There are plenty of examples here of that working out fine. You may want to do stepped starters. I've seen it suggested to give one day for each month out of date when planning lead time for the starter.

With anything that old I start with small steps ie 250 ml starter then 500 ml to 1 liter and go up as needed. The first step might take 2 or 3 days to get going but the next steps are usually done in less then a day so the yeast are real hungry and healthy. Just use yeastcalc to figure out how big of a starter you need and just allow time to chill and decant between steps.

Thanks for the advice. Fortunately, the next batch is a fairly low-gravity mild ale so massive numbers may not be needed.

I put up a starter Saturday afternoon. As of this morning I have a wonderful yeast culture! Plan to cold crash tonight and brew tomorrow.

I am routinely bad about delaying brewing and I consolidate my homebrew orders, so often find myself using the WL products near or after their expiry date - and have never had a problem.

I just successfully brewed a batch with WL006 Bedford yeast that was dated Nov 2011. That was so old, I decided to make a starter (my first ever in nearly 30 years of brewing), as I had bought a flask in order to play with the idea of saving yeast from batch to batch (instead of just brewing second batches on the lees of a first, which I have been doing successfully for ages). It worked like a charm and have saved four scoops of the leftovers in sanitized beer bottles for more!

Even better, I bought the starter flask just about two years ago, but never had the time or courage to try it. However, I did save three scoops of WL007 and three scoops of WL002 in bottles in the fridge at the time... So guess what? Out came the flask again – and it worked on my two year old yeast savings. Both types have come back clean.

I always second guess myself about sanitation, so tasted a small amount of the clear beer (sitting above the saved yeast) before making the starter and from the murky stuff above the starter pancake before pitching to detect any weird or off flavors, when I could abandon and use a new tube. Luckily none so far (out of just three I admit). I am however, thrilled to see my future yeast per batch cost dropping to next to nothing.

I read somewhere that four generations is about as far as you can scavenge / step up before odd mutations develop. I might keep some running and running though to develop “house yeasts” so long as they taste okay.