[el_capitan]

I've been planning a kolsch for my next brewday, so today I pulled out my jar of slurry.  I thought I had harvested it in March of 2013, and I've revived yeast that old before. 

Well, just after I pitched the slurry into my new starter, I looked again and it was harvested in March 2012. 

So what are my chances of reviving anything viable?  On one hand, I feel like I might as well just dump it right now.  On the other hand, it's already pitched and on the stirplate. 

I guess the worst case scenario would be to buy a fresh smack pack, which isn't a big deal at all.  Hmmm... what would you do?  Give it a few days and watch for some activity?  Even if something does start up, I don't know how much I'd trust it. 

[pinnah]

I love experiments and have had my share regarding old and potentially marginalized yeast. 
Probably because one of my faults is being a silly miser
who saves everything with the intent of needing to use it someday.

That said,
my most recent opinion is...not really worth it...especially if you have reasonable access to fresh.

Could you potentially make beer?  Highly likely.
Will it taste like a crisp Kolschy?  Maybe not.
Is it worth 5 gallons - or 3 - of ehh OK beer?

Will be interested to see what everyone else might say...hey, you have all night to watch it grow. 
But what will it grow into...mmuuuhahahahahaha.

Cheers.

[Joe Sr.]

That's pretty old.  I keep my yeast for a long time, too, but that may be pushing it.

Since you pitched into the starter, you'll know soon enough.  If the starter seems OK you can take the risk and pitch it.  Probably not a huge risk but with the time and stress on the yeast you may not get what you're hoping for.

I'd probably trot out and get a new smack pack, myself.  I just dumped some yeast from my fridge last weekend that was a wee bit old and I figured it was time for new.

[reverseapachemaster]

It's not like the yeast have become zombies and your beer is going to turn out awful. Either there are not enough live yeast and you won't see fermentation or you massively underpitched in which case you'll probably get more yeast character in the beer. Perhaps some undesirable off flavors too.

You could let it ride and see what develops but if you are more concerned with the quality of the beer than turning it into an experiment now would be the time to pitch fresh yeast.

[Joe Sr.]

It's not like the yeast have become zombies and your beer is going to turn out awful.

I agree.  I've seen performance changes on successive pitches, though, and that's where I'd be most concerned in a lighter beer like a Kolsch.  You're looking for a certain flavor profile and there's not as much room to hide as there would be in a big stout or something heavily hopped.

The biggest change I've noticed in yeast is reduced flocculation and not flavor characteristics.  My guess is that I get less of the most flocculant yeast when I harvest the yeast cake (though I do my best to get the entire cake, there's always some left in the fermenter).  Gelatin does the trick, though, so I don't worry too much.

[euge]

I just threw away a couple wlp vials (unopened) from 08. Looked a little dark and autolyzed inside. Figured something a little fresher was a better bet...

[el_capitan]

This jar of slurry was actually 3 pint jars that I combined, so there was a lot of slurry in there.  You wouldn't believe it but the starter is fermenting strongly today. 

Still, I think I'm going to pick up a fresh smack pack for this batch.  I kept the starter going just to see if 2-year old yeast would reboot, and it appears that they're doing ok after all.  But you're right, not worth risking the batch and choking down or dumping 3 gallons of beer. 

[dkfick]

I wouldn't use the yeast... I think you're looking at 2 issues.  First the cell count.  Second is yeast mutation... Will the yeast still have those characteristic kolsch flavors? Who knows.

I think it's likely there will still be some living yeast cells in there and you can ferment the beer with it... But there is a potential for alot of time to be wasted to save a few bucks...

[reverseapachemaster]

If the starter is working I wouldn't toss out the yeast without seeing what it can do. I'd try it out on something to see if the yeast are still making beer you want to drink. Maybe a small batch of something simple so you can see what you have.

[ynotbrusum]

I doubt mutation would be an issue, but how robust the yeast would be - that is open to question.  Storing a slurry for an extended period is not ideal (slants or freezing in glycerin is better).  Each successive generation is open to bud scarring and mutation (genetic drift), but if the slurry was from an early generation, the few viable yeast in the slurry should be okay to step up.  Obviously decanting is important and with a huge pile of slurry, I'd be more concerned with getting the healthy yeast and leaving the dead cells and trub behind.

[Poobah58]

I've used yeast that was 3.5 yrs old. I started slow. Like 500ml. Kept ranching up rather slowly. Make sure yeast is done at each stage. Took me 2 weeks but made some good beer!

[ynotbrusum]

I've used yeast that was 3.5 yrs old. I started slow. Like 500ml. Kept ranching up rather slowly. Make sure yeast is done at each stage. Took me 2 weeks but made some good beer!

Glad to hear it - how did you get the good yeast separated from the dead yeast and trub int the slurry?  Any washing or rinsing involved?  I have some well preserved slurries that I wouldn't mind reviving (Platinum Collection strains, for example, that are not always available).

[euge]

I don't doubt it would make good beer! My thought are of potential bacterial presence extant in the slurry. Also, as mentioned before remaining true to the desired strain is dubious. Frankenyeast can make great beer, but you might end up with yeast that don't flocc well or have poor characteristics.

[el_capitan]

The starter actually took off like crazy - again, I had about 5 oz of thick slurry in a 1 Liter starter.  So something in there is still viable.  But like euge said, I don't know how much bacterial contamination there could be.  This is only generation 2 yeast. 

After I realized how old it was, I really didn't intend to pitch it.  More curious to see if it would wake up.  I'll start with a fresh smack pack and make it a point to brew kolsch at least once a year! 

[reverseapachemaster]

You can acid wash to kill the bacteria off. It won't knock off wild yeast but when rinsing yeast you always run that risk of a little wild yeast getting in the mix.