It's really kind of the -- the crux of the -- of the brewer, brewer's job when they're designing a recipe and you're getting into fermentation.
My -- my take on it is that you want to control every single parameter that you possibly can, and so you can completely manipulate this organism to do exactly what you want.
So number one is the strength of the wort, and so you know that if you've got a high-strength wort, then you're going to be promoting more yeast character out of that -- that beer.
It's going to be producing -- or it's going to be working through more sugar, more fermentation, but also a higher-strength beer puts a little more osmotic stress on the yeast and so it's going to drive kind of a higher ester profile.
Next thing, temperature, incredibly important --
and we all know this as brewers, but really manipulating that temperature, you can -- you can come up with dramatically different beers.
Higher temperatures tend to promote a little more estery beer; lower temperatures are going to slow that down a little bit and reduce the ester profile.
Actually, the way I did it -- and I think we touched on this earlier, Chip -- is with my -- with my beers that I -- that I like to have a little cleaner profile on them,
I'll start cold but only for a short while, for about 48 hours, and then I'll drive the temperature up.
And so during the -- the major part of -- of yeast propagation and fermentation, it's -- it's colder and a little more controlled,
and then once the -- the strain is mostly up to terminal population, then we're going to drive that.
And you've minimized the enzymes, so you're going to convert to the esters, and so if you don't have those enzymes available, then you can drive that a little bit warmer and finish it off,
and you can come up with a fairly clean profile as well as finishing out in a decent rate and minimizing diacetyl at that point as well.
Because really what we want is we want complete fermentation.
The other point, pitch rates, incredibly important, and we talked earlier about a range of pitch rates.
And for most of my ales -- and this really depends --regardless of density or specific gravity, I like to pitch fairly high. I like to pitch around 18 million cells per mL.
And if I was going to go above, you know, 18-or-20-Plato beer, then I would probably pitch a little bit more than that.
But anywhere from a 10-Plato to a 17-Plato beer, I'm pitching on the high side. I like that profile.
I pitch higher, and you're going to minimize some of the bi-product.
You're going to get the yeast character but it's not going to be out of balance.
And I guess my ultimate goal in controlling all this is to come up with a balanced -- balanced beer.
You also mentioned mutation, and typically we're not going to see a lot of mutation, or at least in -- especially within a few generations.
If you're harvesting and repitching and harvesting and repitching, you're not -- you're not going to see a lot of mutation.
And especially if you do see a mutation, it's probably not going to come across in the flavor profile.
You may see a loss in flocculation. That's one of the first genes that's typically seen.
But you won't necessarily have a non-phenolic -- yeast term, phenolic. It's not going to really kind of mutate and take on a life of its own.
That's not to say that over the course of long generations, you can't -- that can't happen
-- or not necessarily the phenolic side, but you can't kind of I guess play God and produce this -- you know, this -- this signature yeast.
But if you are going to do that, you're going to want to pitch low.
Typically homebrewers, if they're going to repitch, then they repitch on an entire cake of yeast,
and when you do that, you're pitching a ton of yeast into a very small amount of beer.
If that's the case, that yeast is not going to grow very much.
And what you want to do is you want to drive growth, and so you're probably going to want to pitch on the lower side.
And I guess I'll just kind of go through how I would set up this experiment if I was going to do this, and I've thought about this before.
I -- I'd pitch relatively low and try to -- try to come up with basically maximized growth.
Make sure you have sufficient oxygen, and then -- which is probably about 6 million cells per mL, which is actually about what our package does.
You're going to get about three -- three to three and a half doublings in there. You're not going to get a lot more.
Let that settle out, harvest the yeast, and then pitch about 100 mL of that slurry into the next batch.
Something you could also do is maybe hitting it with intermittent oxygen.
Oxygen is going to allow it to grow more and continue the growth process.
And so, I mean, you could mess around with this and take it out a lot of generations and see if you can change it.
Some of the data that was done at Bridgeport Brewing out in Portland, or some -- some testing years ago showed that after something like 100 generations of yeast
-- or it was a very high number of generations of yeast -- the fingerprints of the -- of the original culture and the final culture were identical.
And so they really didn't see a lot of genetic shift in that. But at the same time, that could be a function of the strain that was being used at the time.
So, you know, I don't -- you know, ultimately I don't think you're going to see a lot of mutation, but, you know, it could happen.