Yeast Generation Confusion

I have some confusion regarding what makes a yeast generation. I understand that if I buy a vial of yeast and use it to ferment a batch of beer, harvest this yeast, and then re-pitch it I am pitching a 2nd generation yeast.

But what about starters? Lets say that I freeze this 2nd generation yeast, then at a later time, make a 2 stage starter from it and then pitch it. Now, am I pitching a 4th generation yeast (because of the 2 starter stages) or am I pitching a 2nd generation yeast?

Very good question!!

My assumption has always been a fermented batch of beer dictates a new generation due to the workload/stress the yeast go through aerobically and anaerobically.

I've never thought of a starter as iterating the generation mark. The mostly aerobic environment, low stress, lack of hop oils, etc makes for a "warm and fuzzy" environment. BUT, then again, the yeast ARE creating a new generation of yeast in there so maybe it should be considered a new generation.

Very good question!!

it's a fairly arbitrary distinction anyways as it's not based on actual population growth, although it's definitely a helpful concept. i have never heard of anyone count the starter as a generation. they are pre-season games.

BrewerDon said:

But what about starters? Lets say that I freeze this 2nd generation yeast, then at a later time, make a 2 stage starter from it and then pitch it. Now, am I pitching a 4th generation yeast (because of the 2 starter stages) or am I pitching a 2nd generation yeast?

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There would be no logic in calling a starter step a generation in the sense brewers think of their yeast as a 'generation'.
When we put viable cells into a volume of wort(lets call it a starter) they will bud and create other cells which will likewise bud into more cells and so on. How many times they bud and hence multiply within a single step starter depends on the amount of fermentable sugar in the wort vs the number of cells pitched.
If the yeast pitching rate is high(large number viable cells/ml wort) then there will be likely only one or less new generation created. If the yeast pitching rate is very low then there could be more than one generation of budding.

My view is that if optimum handling practices are maintained with all aspects of the starters (sanitation, yeast health, temperatures, storage methods, etc) there should be minimal stress on the yeast. I would therefore not consider a starter step a generation.
However if care is not taken the yeast can be stressed even in a starter and that will effect their health moving forward. It may not kill them but they might end up as poor specimens to form a base for your future brews.

We often talk of yeast viabilty (are they alive or dead) and calculators estimate this based on age.
One thing that calculators do not estimate and that is the vitality of the living yeast and that depends not only on age but the stress they suffered.

Thanks for all of the great insight! My question was based on my plan to start freezing yeast and starting a yeast library.

To build up my library, I plan to buy a vial of yeast (if that type is not already in my library) for my current batch of beer, make a stepped starter large enough to pitch in my current batch of beer but with enough extra yeast from the starter to save 2 50 ml vials to freeze.

In the future, whenever I use the last frozen vial of this type of yeast, I will again make a big enough starter to save 2 more 50ml vials.

I was trying to figure out at what point I would need to purchase a new vial of yeast with this method.

I often hear people talking about re-pitching for ONLY x number of generations.

Based on the responses above, it sounds like if I use good practices, I will never have to buy a new vial of yeast that is in my library. I can just keep propagating the yeast that I started with.

Does anyone see any issues with this plan?

BrewerDon said:

Does anyone see any issues with this plan?

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perhaps a better way would be to save some of the original as master stock and use this to start new pitching cultures. this is what i do anyways. the advantage is that you are starting each time from a very clean stock that you know is the same thing, behaving the same way and uncontaminated. i could imagine that even with great brewing practices (which are by their nature not sterile) you can eventually accumulate some lacto bacteria or something, say over 20 generations, but i don't really know.
the disadvantages are that you will be starting from a much smaller culture and have to step up more, therefore more chance for contamination if you are doing this at home. (normal practice in a yeast or bacteria lab, but done in very sterile conditions) but any contamination or mis-behaving yeast is only transferred to subsequent batches from that same pitch, so you can always throw it out and go back to the mother culture. also ideally you would streak out some cells on a plate and make the first starter from those, and that's a real pain to do at home.

BrewerDon said:

I often hear people talking about re-pitching for ONLY x number of generations.

Based on the responses above, it sounds like if I use good practices, I will never have to buy a new vial of yeast that is in my library. I can just keep propagating the yeast that I started with.

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I recommend you have a watch of this video presentation with Neva Parker of Whitelabs.


She discusses the generation question around about the 32.30 minute marks of the video.

dinnerstick said:

perhaps a better way would be to save some of the original as master stock ...

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My plan was to take the original stock, make a large starter, and then save a portion of that as that master. Are you suggesting that it would be better to save some of the original before I make a starter with it?

When I save a vial of yeast, I am wanting to save about the number of cells that one would get when buying a vial of yeast. That way, even though some cells will die in the freezing and storage process, I will still have a good number to start with when I take that vial out of storage and step it up to pitching levels.

el_caro said:

She discusses the generation question around about the 32.30 minute marks of the video.

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That was a very informative video but when she talked about "generations", she was referring to reusing yeast from a previous batch - harvested yeast.

I am considering stepping up the original vial of yeast that I buy and saving some of it. I would continue to build up that yeast before ever pitching. This way, I don't need to worry about yeast harvesting and washing.

She did give some good points about being able to use yeast for a lot more generations when you take good care of it.