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Old 11-27-2009, 06:40 PM   #1
kunstler
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Default crossing yeast strains - creating a "House strain"

post disclaimer:
I am no where near anything close to a scientist. a love for physics and chemistry in highschool and brewing is about as close as I come.


I have played with the idea of having a house yeast that I use - with all beer, it evolves to what we like and then we keep it there. I would like to know if this can be done with yeast.

obviously since they are single cell organisms they do not mate thus mixing characteristics that they pass along, but the enviroment they are in greatly determines their reproduction - if they are stressed vs don't have to work at all.

With that in mind could you introduce two yeast strains to each other and end up with a generational mix if you keep harvesting, washing and re-pitching. Will they genetically end up crossing and giving you characteristics from both yeast (or some from one and some from another or some characteristics will be less dominate). Or will I just end up with yeast that is just some of this some of that that happens to be all mixed together.

Obviously the results will end up being very similar in initial generations, but if you keep harvesting yeast and re-producing if they don't cross you can not guarentee a 50/50 mix of one strain to another.

does this make sense?

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Old 11-27-2009, 08:53 PM   #2
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If only it were that simple. Yeast reproduce by splitting cells, not humping each other, thus two yeast cells won't produce a unique offspring together.

That's not to say your idea doesn't have merit. You should look at this month's BYO magazine. One article in there, the author tried using different strains on the same wort to produce more attenuation with fewer esters.

Much of what you'll read says "one strain of yeast will out compete the other" but after reading his article, that doesn't seem to quite be the case. I'd agree that you won't get a 50/50 split...on yeast will definitely dominate the batch, but the other yeast will still have an effect on the finished beer.

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Old 11-27-2009, 09:00 PM   #3
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+1 asexual reproduction means no cross-breeding. But it does mean mutation. If you really want a "house strain" you could look into capturing wild yeast. Once you have a culture, you can run a few batches, selecting for more flocculent yeast each time. You won't be able to choose ester qualities you want, but you would have something unique.

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Old 11-28-2009, 01:34 PM   #4
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I knew I couldn't have them go into a dark room and play some soul music and get something but the info does help.

Is it possible to get a positive mutation on the strain that can then be isolated and reproduced - or is mutation only equal bad effects for beer flavour/profile that would only be passed along?

I'll def. have to check out the BYO article online.

Thanks for the info.

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Old 11-28-2009, 01:38 PM   #5
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I have no idea what im talking about but I had this thought:

Some of it would have to do with when you harvest the yeast in getting more or less floculant yeast

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Old 11-28-2009, 07:16 PM   #6
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Yeast, like all other fungi, can 'sexually' reproduce. All fungi can produce spores of two different mating types, mostly during starvation conditions. When conditions are better and they find an opposite mating type, they can join (regardless of specific strain dna types) and form a full diploid cell.

So yes. In my experience you have to start with two main things:

1.) Yeast has to be diploid, meaning the strain has to have two copies of it's DNA in the nucleus (Just like we, as humans have) so that the cell can have the option of making four spores from one cell (two of each mating type).

2.) Bad conditions. Usually this means nitrogen starvation, in our lab we design yeast food specifically for this purpose. I suppose you can also leave yeast out on a yeast cake until it is just about to dry up. (You can check under any microscope if it is sporulating.) Word on the street is that V8 juice provides excellent conditions for sporulation.

Then do this to two strains, and then mix them in nutrient rich medium together. The problem with this is separating out the three resulting strains- the two old ones and the new one. This is where we plate out the result, and find individual cells to look at under the microscope.

One problem in nature is that mixed breeds do NOT do well in the first generation of mixing. (They really do well considering fitness, but the DNA is not stable) This is true for yeast. So we then take the resulting strain and starve-sporulate it again and THEN the resulting yeast strain tends to be stable and maybe, just maybe, unique from the parents.


Check this out for more in-depth info:
http://www-sequence.stanford.edu/group/yeast_deletion_project/aims.htm

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Old 11-28-2009, 09:09 PM   #7
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now when you have the 3 strains will the first two origional strains continue to reproduce alond side the new 3rd strain if you don't seperate the 3rd strain and starve-sporulate again?

And if thats the case, the 3rd strain won't be as stable genetically and I'll basically be back to the first 2 strain - thus basically I'll have the same results as pitching two different yeasts. Is this right?

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Old 11-28-2009, 10:26 PM   #8
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Quote:
Originally Posted by kunstler View Post
now when you have the 3 strains will the first two origional strains continue to reproduce alond side the new 3rd strain if you don't seperate the 3rd strain and starve-sporulate again?
From my understanding, yes. Although our lab works with completely different species, S. cerevisiae and S. bayanus. Where as you *might* get lucky with different strains of S. cerevisiae, as they are much more similar.

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Originally Posted by kunstler View Post
And if thats the case, the 3rd strain won't be as stable genetically and I'll basically be back to the first 2 strain - thus basically I'll have the same results as pitching two different yeasts. Is this right?
In my experience, yes. BUT there is hope! I thought about this some more, and you might be lucky enough to have a stable strain because they are so similar...

If I were pressed to cross two beer strains, that I assumed were diploid, here's what I would do.

1.) Starve them somehow- Maybe let the dregs after bottling the two beers sit with no beer on them for two days or so.

2.) Check for spores in both (via microscope, a cheap sixth grade science fair one should work). Of course, not all will be spores, but as long as there are a few, you should be ok. If you are curious as to what these look like, just google image search yeast spores.

3.) Mix both in a large beer wort and let the yeasties have their fun.

4.) Get access to petri dishes and agar. There are a few options here for the homebrewer. You can order these online. You can also try to use mason jar lids (that are in one piece.) And mix unfermented beer wort (doesn't have to be hopped) and boiling agarose and let settle. Be sure to be sterile here!!!

5.) Drop a very small amount of the results of 3 on the 'plate' from 4. Now you are aiming for a very small amount, so just a drop from the beer, not the yeast cake might work. The point here is to isolate individual yeast cells on plates.

6.) These individual yeast cells will grow up on the 'plate' after 2-5 days and you hopefully can assume that these are isogenic- meaning they came from just one cell. Now to test what these strains are, we don't have to do DNA testing, what we can do is just brew several 1-gallon batches of similar beer and taste the outcome of what the yeast will do to each beer.

7.) Hopefully you will have about 3 slightly different tasting beers with different attenuations. And knowing your original two yeast strains and their effects on the beers, maybe you have a new strain??

--This would be my best effort, having only access to a cheap microscope (~40-80$) and access to agarose and petri dishes (ordered online).

This sounds actually kinda neat. I might try this one day.
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Old 11-28-2009, 10:59 PM   #9
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Sweet - It would be neat to be able for one to say "this is my yeast" not "this is american ale #blah blah blah"

and in the worse case what do we loose, some time and some money learning, and some disposable yeast.

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Old 11-28-2009, 11:11 PM   #10
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It may be simpler to use a selection process instead of forcing sporulation. Your typical conditions doesn't exactly mimic the sterile enviroment of a bio-hood in a well equipped laboratory.

By harvesting cells at certain times during the fermentation process you can select for specific traits. More flocculant yeast will settle out quickly during the primary, less flocculant cells can be harvested from the secondary. More alcohol tolerant strains can be found after secondary fermentation.

Just a thought, there are dozens of variables to play with.

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