Zombie Yeast - How old - is too old?

Australia & New Zealand Homebrewing Forum

Help Support Australia & New Zealand Homebrewing Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Reaction score
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 shits 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 shit for destroying the kitchen.
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.
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.
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).
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.
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.
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.

Latest posts