You build up a starter, brew a beer with it and harvest that slurry.
Is that Generation I or Generation II?
I’ve always called it Gen II…what say you?
I would say Generation 1: it’s been through one stressful reproduction/fermentation cycle.
The yeast that comes out of the smack pack is Gen 0, the known quantity, the baseline.
I count mine the same way Sean does. Building up the cell count doesn’t seem like a generation to me. Making a beer with it does.
Are we counting generations due to “contaminants”? The reason I’m asking is Kaiser will use a microscope and loop to make sure he has great yeast. So if he did this every round and built it up on a stir plate, would he be perpetually at gen0?
I think that even if you use a tablespoon of slurry and “re-build” it that would be Gen 1
I asked this question a while back on the NB forum. I don’t remember what the outcome was mainly because I think it was inconclusive.
If you build 100 million cells into 400 million wouldn’t that technically be 2 generations, 800 would be 3 and so on.
The way I tend to look at it is every time I use a slurry because alot of the cell count is there and not as much yeast growth has to occur so the same yeast is put to work again. I’m not sure how oftern they die and regen during fermentation so I may be off here but that’s my current view of it.
Biologically and philosophically, you are 100% correct. All life comes from pre-existing life.
However, it appears that the “generations” term is used amongst brewers to indicate how many “brew cycles” the yeast has been through. “Brew cycles” meaning “how many times the yeast culture has been used to make a batch of beer.” The concern is the potential contamination of the original culture (by bacteria and wild yeast) as well as spontaneous mutations within the culture. Most of us count the way Sean and Denny do (from zero; so the first batch of beer = the first generation).
Some big breweries may go 20-40 brew cycles (or “generations.”) but it is recommended by some that homebrewers should not use a yeast culture more than 3-5 brew cycles, even if their “sanitation” is pristine. That advice is probably wise as I don’t have laminar air flow hoods, rigid temp controls, SS fermenters and CIP processes like the big brewers do. Plus, a fresh batch of yeast is only about $5-6 bucks. Using really aged yeast that hasn’t been put through a starter or is several generations old is risking an infection or off flavors in your beer–it just isn’t worth it. At this time, for me, it is less work to just buy another fresh batch periodically than to do all the yeast ranching and acid washing that yeast farmers do to ensure purity of their cultures.
One of my friends has done 20 batches off of one vial/pack of Chico Yeast. No problems, but he is an accomplished brewer who makes very clean beers.
You don’t need a laminar hood. An alcohol lamp will cause an updraft, so that is all you need according to MB Raines during a talk at last years NHC.
Unless the Lord is creating little yeasty Adams and Eves at the White Labs factory, you will never have “generation 0” yeast from a biological point of view. The term is really for tracking how many fermentation cycles a certain culture has been through. Since a constantly oxygenated starter is mostly about cell growth and is not a stressful fermentation environment, I wouldn’t count it.
I’m with Sean and Richardt that we mean brew cycles when we talk about yeast “generations”. It’s way too difficult nor practical to go by actual yeast generations.
For my yeast bank I keep track of all re-culturing that is done for the yeast bank maintenance. These steps too could be called generations.
Kai