Zombie Yeast - How old - is too old?

[Hazah]

So, I have been cleaning up the “spare” fridge in the garage at the insistence of SWMBO and behind the crisper draw I managed to find three smack packs of Wyeast manufactured in May, Jun and Jul 2017.

I thought to myself that they would be toasted by now and was going to throw them in the bin. For ***** and giggles I popped the inner bag on all three packets shook them and just tossed them up on the bench and continued to clean and forgot about them as I was being handed the new list of stuff that needs to get done

When I came back out after dinner about (8hrs) to my surprise all three were swollen like a fresh pouch does – so here’s my question – do I put them on the stir plate in some fresh wort and step them up like I normally do and salvage them or am I going to end up with something I don’t want to use in a batch of beer due to the age of it? Am I going to end up with some kind of Zombie Yeast?

I have bought saved yeast slurries back to life after 6 – 8 months before – but is over six years old taking the piss a little bit too much?

I would be keen hear what others think before I get all excited and boil up some DME and get in the **** for destroying the kitchen.

 

[yankinoz]

Old yeasts never die, they just fade away.

Much older yeast than that, e.g., from old bottles of a beer, has been cultured and used successfully. It's no surprise you have some active yeast; the problem is you don't know how much. If you're working on 20L of wort at 1.05, pitching all three without a starter would probably give you an underpitch, but who knows? I'd pitch all three into a starter or the rubbish bin, depending on circumstances. Some on this forum may have applicable experience.

 

[DucatiBoyStu]

Make up a low SG wort, and just treat it like normal yeast.

Thats what I have always done. I have always found a low SG starter is best, then step it up.

 

[bradmcm]

I smacked a pack of 2308 Munich Lager that was 12 years old and it went just fine. (I let Wyeast know and they were very impressed).

 

[Hazah]

So I have managed to get a starter which I stepped up from 1 litre to 3 litres up and going at a gravity of 1.030 and it took off like a rocket on the stir plate.

It just goes to show that if you have an expired yeast pack it might be worth trying to make a starter with it rather than the default of binning it and buying a new packet of yeast.

It might be interesting to see if the White Labs packaging holds up as well as the Wyeast smack packs over time - due to the small window on the packaging - I just don’t want to wait around 6 years to find out

Thanks for the advice team.

 

[MHB]

Old yeast has a bad habit of mutating, particularly Lager yeasts.

Yes it can still be viable and I too have found the odd old yeast in the back of a fridge, one was a Czech Pilsner that threw lots of really strong sulphur notes.
If you were going to use an old yeast it would a good idea to build it up (make a starter) and restore its vitality as well as proving its viability. Then perhaps pitching it into a cheap kit or low cost brew to prove its going to give you the traits you are looking for.
There is a very good chance it won’t perform as expected and I would be reluctant to put it into a brew I was highly invested in.
Mark

 

[Lefty]

For the small cost of $ 2 for the LDME and 36 hours on the stir plate, give it a go. As above you may well be surprised.