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Old 01-15-2010, 07:14 PM   #1
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Default Anyone Ever Tried Engineering Yeast Strains?

Hey all, this is my first post in these forums. I'm pretty new to brewing (have my second batch ever in the primary right now), but I've learned a lot pretty quickly.

To get right to the point, I have a unique (well, presumably so) strain of yeast that I have acquired. This is the strain that I have used to brew so far, and I intend to keep it that way.

However, I've had a thought. I'm planning on harvesting and reusing yeast (as opposed to making a starter from a slant every single time), and I was wondering if anyone had ever kept a persistent strain of yeast.

My thought is that each "major" type of beer that I brew could have its own specially adapted yeast cake associated with it. I could brew, say, my RIS, harvest and save the yeast cake, and use THAT yeast cake again when I brew the RIS. Repeat this process and I'll be placing some artificial selection pressure on the yeast, forcing them to adapt to the specific conditions of that beer.

Has anyone tried anything like this before?

tl;dr: I want to reuse the same yeast cake for a particular recipe, over and over again, until that yeast is perfectly adapted to that beer. Thoughts?

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Old 01-15-2010, 07:17 PM   #2
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Isn't that what yeast labs do?

And, over generations (sometimes a few, sometimes many) yeast can degrade itself.

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Old 01-15-2010, 08:18 PM   #3
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In theory I think it's great, but I just don't trust that a homebrew setting has enough control over major factors, especially cleanliness.

Also, how many separate yeasts would you want to maintain? If it's one per style, I hope you have a big fridge. Not to mention the shelf life - if you're trying to avoid doing starters, you'll need to constantly brew with each strain of yeast to ensure you have enough active cells to pitch into beer. If they sit around too long, your viability will dramatically decrease and you'll be required to make a starter.

But I like your thinkin here... I think your better bet would be to find a strain of yeast you like and use it in almost every beer. While it won't be adapted to a particular style/recipe you brew, at least it'll be selected for your brewery.

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Old 01-15-2010, 09:52 PM   #4
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Yes, yeast labs engineer strains of yeast to be adapted to certain beer styles. I'm basically trying to turn myself into a yeast lab. :P

I'm basically looking at keeping 3 separate strains going, each one adapted to one of my 3 (planned) "flagship" brews. I'm not necessarily opposed to making a starter every time, just so long as I'm not staging up some ridiculous number of times. Starting with an inoculation from a slant is, well, time-consuming. I'd much rather pitch a whole ton of yeast to start with.

The main reason I want to do this is because, as I said, I have a unique strain of yeast that I'm using for my brewing. I like the concept of having a beer that I own almost entirely, down to the yeast. If I could, I'd grow my own hops and barley, and malt and roast it myself. Perhaps one day. :P In any event, I really want to stick with this unique yeast type and try forcibly adapting it.

I know that yeast cultures degrade with time (all microbial cultures degrade over time), and I'm prepared to do frequent passages to ensure that I always have a healthy population. Anyone know roughly how long a yeast cake stays viable? I would think not much longer than 6 months in cake form, but I know that slants can last a while. I'm thinking of making slants to serve as a backup to every cake that I make, just in case the cake dies before I use it. Thoughts?

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Old 01-15-2010, 10:09 PM   #5
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In my humble opinion, I think that if you were to get serious about this, frozen cultures would be absolutely necessary. The only way to be assured that you have pure culture is to start from a pure culture. If you were to just repitch every time, you could not be assured that the yeast cake is 100% yeast. There are also other problems:

1) Repitching everytime builds up a lot of trub on the bottom. Even after two re-uses, I've seen my yeast cakes get about 6 inches thick. If you attempt to dig in there and only re-use a portion, you had better use a sterile hood. It is almost impossible to prevent some sort of contamination, especially over a long period of time.

2) There is an argument out there that deserves attention, with yeast going through, literally, hundreds of thousands of generations, there is a very very high chance of mutation or adaptation. With the former being more rare and more troublesome. Sure, it may not have a noticeable effect on the beer, but it can change other important things (pH tolerance, attenuation.. etc).

I also highly recommend storing tiny vials of the yeast with 30% glycerol in the freezer. You can get hundreds of starters from these with a lighter and a metal wire. Just dip the wire in ethanol and flame it to sterilize it. Then dip it in the frozen tube and just touch it to the frozen yeast. Now all you have to do is carefully touch the tip again to a starter solution. Wa-la- your yeast starter is going. And if we were careful enough, it will be close to 100% yeast.

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Old 01-15-2010, 10:19 PM   #6
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Quote:
Originally Posted by toastermm View Post
In my humble opinion, I think that if you were to get serious about this, frozen cultures would be absolutely necessary. The only way to be assured that you have pure culture is to start from a pure culture. If you were to just repitch every time, you could not be assured that the yeast cake is 100% yeast. There are also other problems:

1) Repitching everytime builds up a lot of trub on the bottom. Even after two re-uses, I've seen my yeast cakes get about 6 inches thick. If you attempt to dig in there and only re-use a portion, you had better use a sterile hood. It is almost impossible to prevent some sort of contamination, especially over a long period of time.

2) There is an argument out there that deserves attention, with yeast going through, literally, hundreds of thousands of generations, there is a very very high chance of mutation or adaptation. With the former being more rare and more troublesome. Sure, it may not have a noticeable effect on the beer, but it can change other important things (pH tolerance, attenuation.. etc).

I also highly recommend storing tiny vials of the yeast with 30% glycerol in the freezer. You can get hundreds of starters from these with a lighter and a metal wire. Just dip the wire in ethanol and flame it to sterilize it. Then dip it in the frozen tube and just touch it to the frozen yeast. Now all you have to do is carefully touch the tip again to a starter solution. Wa-la- your yeast starter is going. And if we were careful enough, it will be close to 100% yeast.
Well, #2 is sort of moot because I'm TRYING to mutate the yeast. The idea is to dedicate one strain to one beer type.

I've been wondering about cryo-storage. I should throw this out there for a little reference: I'm a professional microbiologist, specializing in bacteriology. I know a good bit about cryo-storage of bacteria, but yeast is a different beast. I wasn't sure that they would do well in cryopreservation. Are you saying that a standard household freezer is sufficient for long-term storage? That would be a hell of a lot simpler than a -80C chest freezer or liquid nitrogen storage, I can tell you that. :P

Obviously, I have no idea how problematic contamination would be, but I'm pretty good with my open-air aseptic technique. A hood doesn't really do much for keeping a culture pure; the primary purpose is to separate the microbiologist from his work. I'm pretty confident that the minute airborne contaminants wouldn't be able to out-compete my yeast culture provided I take sufficient sanitary measures. Then again, I don't work with yeast routinely, so I'm not sure how readily they out-compete other contaminants.
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Old 01-15-2010, 10:39 PM   #7
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As for your earlier question about viability, if you check out Mr Malty's pitching rate calc, it figures that if you save slurry from another batch, its viability decreases to 10% after about 8 weeks (and doesn't go any lower than 10%).

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Old 01-15-2010, 10:53 PM   #8
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As for your earlier question about viability, if you check out Mr Malty's pitching rate calc, it figures that if you save slurry from another batch, its viability decreases to 10% after about 8 weeks (and doesn't go any lower than 10%).
Hm, so that would pretty much necessitate making a starter every time. That's sort of annoying, but not too bad.
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Old 01-15-2010, 10:58 PM   #9
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What is so special about this yeast?

Half the fun of brewing is experimenting with different yeast strains. I don't know if you will have too much luck mutating the yeast, unless you are going to apply some reverse genetic techniques. For the most part you by adding pressure to your system you will just be selecting for variants all ready in your population, and for that part you will not be eliminating the traits you don't want but more over reducing their overall % in the total population.

Many Characteristics that yeast impart to beer are from the strain, but also you have to consider fermentation temperature and fermentation volume as well as many other factors.

A lot of brewery's have house strains of yeast,and like many of us home brewers, will re-use these yeast several times over the year. The brewers will uselessly have a lab such as White labs or Wyeast maintain that strain, and have them periodically grow them up a new starting batch that replace the old running stock with. Is this what you are looking to do?

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Old 01-15-2010, 11:01 PM   #10
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It's an interesting idea. I think if you want to get into it, you need to start by reading up on how to slant yeast and how to plate out pure cultures. I think it's do-able in a kitchen setting, so long as you do everything in multiples so you can trash the inevitable contaminated strain.

I've kept yeast slants in the refrigerator door (I know, I know) well over a year and been able to reculture them into healthy starters and make good beer from them.

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