Yeast generations

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Permalink Reply by Smiffy on February 2, 2013 at 12:23am

I don't know how long it takes for a new generation (one reproduction cycle) of yeast, probably only minutes, so yeast taken from one brew is probably hundreds or thousands of actual generations old, but for yeast, the way people usually use the word is for one generation to be from pitching to harvesting.

I've had no problem using the same yeast in four successive brews.

I would say that if you have enough yeast for one brew (of whatever size), and you split that in four, then "starter" that up to enough for your brew, that will be similar to it going from pitching to harvesting once.

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Permalink Reply by Liam Callaghan on February 2, 2013 at 7:07am

As Smiffy says, 1 generation per batch of beer.

If you are careful on your cultivation and wash it you run up to 6, most I have done is 10.  Washing it with cool boiled water and letting it settle, discarding the powdery stuff at the top and only keeping the smooth creamy yeast in the middle section.

The stuff at the bottom (as far as I understand) tends to be dead and possibly died before it reached the attenuation you were after, the powdery stuff on the top tends to over attenuate and not flocculate - this is also more prone to mutation.

I'd recommend 4-6 to be safe as you are always going to get some bacterial or other yeast infecting it.  Saying that, 4 generations gives you a huge amount of beers to brew if your running 25-39 litre batches.  I can bottle 4 samples of each generation from each brew.  Should be enough for a year! 

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Permalink Reply by Hillman on February 2, 2013 at 12:39pm

On this question, I brewed in late-November, harvested the yeast, and haven't been able to brew again. I didn't wash the yeast, just sanitised a jar and put it in the fridge. I'm planning to brew again in about two or three weeks, which will make nearly three months of the yeast sitting in the fridge. Should I use the harvested yeast? I've held on to yeast in sanitised jars in the fridge before without problems, but not for this long. 

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Permalink Reply by Smiffy on February 2, 2013 at 2:23pm

I don't wash my yeast, but I do have a conical, so I drain off the dead stuff which has settled while fermentation is going strong, then drain off the yeast to save after the fermentation has slowed. I have used yeast which has been in the fridge for 11 weeks. (I let it warm up in the jar so it doesn't get a shock by being suddenly warmed up). The advice I was given a long time ago was to smell the yeast, if it smells like it always does, its probably OK, if it smells a bit different, don;t risk it.

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Permalink Reply by Hillman on February 2, 2013 at 2:29pm

I just had a sniff actually and it smells great. And yeah that's what I do with my conical as well -- I'd just planned to reuse it sooner but am moving next week and didn't want to put 40L of fermenting saison in a moving truck.

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Permalink Reply by Tilt on February 4, 2013 at 4:26pm

Aye - great replies and clarification for one of those questions that's bugged me for a while -  thanks fellas.

So the term "generation" is more of a catch all convenience term used to count cycles of major fermentation activity (as you say - 1 gen per batch of finished beer) rather than a precise count of the number of times a yeast cell buds and throws pups as it reproduces through the step up and fermentation stages.  Cool - got it now.

@ Hillman - I've managed to get unwashed, 8 month old, stored in the fridge yeast fired up for a new batch.  I used a three step starter (100ml to 500ml to 2000ml) and decanted off the trub and dead yeast at the 500 to 2000ml stage.  This produced a nice cake of fresh smelling ale yeast which went on to make a decent beer. 

Having said that I wouldn't do it all the time as the risk of infection is higher (and it was more of an experiement to see if it could be done - there was a back up plan waiting in the wings if it didn't)

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Permalink Reply by Liam Callaghan on February 4, 2013 at 5:04pm

From memory the main issue from leaving the unwashed yeast for long periods is weak yeast, the acids from the hops can damage the yeast cell walls so they don't function as well and you could get more mutation.  

I've stored it like that for up to 6 months and used it with no ill effects, equally strong ferment.  Doesn't mean the yeast wasn't knackered though, just that they still did as I expected.

I'm still learning so don't take my word for it :)

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