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Old 10-09-2009, 01:58 PM   #1
hopvine
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My father deals with water treatment in Ethanol plants, so we usually have interesting discussions regarding the parallels between homebrewing and corn ethanol production.

He mentioned the other day that a "yeast expert" from one of the industrial yeast suppliers was telling him about their new strain of yeast that is tolerant of other strains, which opens the door to fermenting a slurry with one yeast in the beginning, and another towards the ends. The guy said that typically when two strains are present, they actually attack each other before processing sugars. I may not have all the details, which leads to my questions...

1) Is this even true, or is it a marketing ploy (because wouldn't you need TWO strains that were tolerant of each other?)
2) If it is true, does beer yeast exhibit the same behavior? Is this why you never hear of people pitching two different yeasts to add to flavor complexity?

 
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Old 10-09-2009, 02:06 PM   #2
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I know yeast, like many microorganisms, creates by-products that are harmful to other types of microorganisms in order to depress or kill them off (this is why a reasonably quick starting ferment is so important). Whether they create by-products that are harmful to other strains of yeast I couldn't say.
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Old 10-09-2009, 03:37 PM   #3

It's not true that people don't add two strains. I've done it. And I've read of others doing it and never heard of any trouble.
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Old 10-09-2009, 03:46 PM   #4
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The only times where I usually use two strains of yeast is on bigger beers. And then I use a beer yeast in the primary and once it's stopped working, pitch a higher alcohol and/or wine yeast to complete the ferment.

In this situation, I've never really had a problem with the second batch of yeast taking off pretty good to complete the top end of the fermentation.

for what it's worth.

~r~

 
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Old 10-09-2009, 03:55 PM   #5

I remember adding two strains at the same time long ago when I was brewing and hadn't made a starter and had two strains available to me. Didn't have any problems at all.
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Old 10-09-2009, 04:32 PM   #6
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Maybe he was speaking of two species of yeast, not strains.

 
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Old 10-09-2009, 04:41 PM   #7
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Quote:
Originally Posted by Teacher View Post
Maybe he was speaking of two species of yeast, not strains.
Thats what I'm thinking. All yeast we use (except lager yeast, lambic blends and brett) is Saccharomyces cerevisiae. Think of it like dogs. All are the same species, but are different breeds.

Either they use vastly different yeast than we do, or he has no idea what he is talking about. Even Brettanomyces and Saccharomyces cerevisiae don't necessarily kill each other in the same wort/beer.


 
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Old 10-09-2009, 05:05 PM   #8
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Quote:
Originally Posted by Teacher View Post
Maybe he was speaking of two species of yeast, not strains.
+1, yeast suppliers even make yeast blends, that in itself negates the argument unless it is species/genus specific.
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Old 10-09-2009, 05:05 PM   #9
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The issue is going to be partly one of cell densities. If you start the fermentation with yeast A, it is going to multiply (growth) before is starts to ferment. So, you have a huge number of yeasties which are then going to start working on making ethanol. If you were to pitch normal amounts of yeast B into this vessel at some later point, what are they going to grow on? Most of the sugar and free nitrogen are going to have been used already by the first yeast. This is one reason why infections are going to be more common earlier on. Once the yeast has taken hold, there isn't much for anything else to use. But if the infection takes hold early, it can out-compete the yeast. This is a practical application of survival of the fittest, if you like.

Pitching two Sacchyromyces yeast - say Nottingham and Safale 05 - at the same time, or even at different times, is not going to get you both flavor profiles to any great extent. One will take off faster, multiplying before the other gets going. Since yeast growth is exponential, even a small headstart gives a large benefit. [There might be some contribution by both, but one will predominate.]

However, with a yeast like Brettanomyces, it can metabolize different (more complex) sugars than Sacchyromyces can. So Sacch can get started, then Brett will take over and finish the job off. So maybe their "tolerant" yeast does something like that?

And all of that is without any additional things like secondary metabolites being secreted that slow or kill other organisms. Here, there are two main classes of compounds. Even a simple prokaryotic bacteria has things called "quorum sensors" (basically primitive hormones) that determine, essentially, how many other bacteria like it are around. Too many, and these molecules switch some genes on/off and the bugs start to go dormant. Yeast are more complex being that they are eukaryotes, just like us. They have even more sensing type behaviours. Thing about factors that trigger them to flocculate, and you'll start to see what I mean.

The second class are molecules that kill other organisms. Yeast and bacteria are in a constant evolutionary arms race. Many of the antibiotics that we use were found as secretions by some organism or other that happens to kill its competitors in natural surroundings. Penicillin is a perfect example of this - secreted by a fungus to kill bacteria, thereby allowing the Penicillium mold to grow bigger.

Maybe their tolerant yeast is resistant to some metabolites that normally kill or stop growth? It could be resistant to an antibiotic normally secreted by Sacch, for example, or insensitive to certain quorum molecules? Or maybe it secretes a drug that kills all of the existing yeast?


The above is the microbiologist in me speaking. I am not a yeast expert at all, so I'm not sure specifically what allows yeast to tolerate other yeast or not... may be worth looking into? Microbiology is fascinating!

 
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Old 10-10-2009, 05:28 PM   #10
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Quote:
Originally Posted by BioBeing View Post
The issue is going to be partly one of cell densities. If you start the fermentation with yeast A, it is going to multiply (growth) before is starts to ferment. So, you have a huge number of yeasties which are then going to start working on making ethanol. If you were to pitch normal amounts of yeast B into this vessel at some later point, what are they going to grow on? Most of the sugar and free nitrogen are going to have been used already by the first yeast. This is one reason why infections are going to be more common earlier on. Once the yeast has taken hold, there isn't much for anything else to use. But if the infection takes hold early, it can out-compete the yeast. This is a practical application of survival of the fittest, if you like.

Pitching two Sacchyromyces yeast - say Nottingham and Safale 05 - at the same time, or even at different times, is not going to get you both flavor profiles to any great extent. One will take off faster, multiplying before the other gets going. Since yeast growth is exponential, even a small headstart gives a large benefit. [There might be some contribution by both, but one will predominate.]

However, with a yeast like Brettanomyces, it can metabolize different (more complex) sugars than Sacchyromyces can. So Sacch can get started, then Brett will take over and finish the job off. So maybe their "tolerant" yeast does something like that?

And all of that is without any additional things like secondary metabolites being secreted that slow or kill other organisms. Here, there are two main classes of compounds. Even a simple prokaryotic bacteria has things called "quorum sensors" (basically primitive hormones) that determine, essentially, how many other bacteria like it are around. Too many, and these molecules switch some genes on/off and the bugs start to go dormant. Yeast are more complex being that they are eukaryotes, just like us. They have even more sensing type behaviours. Thing about factors that trigger them to flocculate, and you'll start to see what I mean.

The second class are molecules that kill other organisms. Yeast and bacteria are in a constant evolutionary arms race. Many of the antibiotics that we use were found as secretions by some organism or other that happens to kill its competitors in natural surroundings. Penicillin is a perfect example of this - secreted by a fungus to kill bacteria, thereby allowing the Penicillium mold to grow bigger.

Maybe their tolerant yeast is resistant to some metabolites that normally kill or stop growth? It could be resistant to an antibiotic normally secreted by Sacch, for example, or insensitive to certain quorum molecules? Or maybe it secretes a drug that kills all of the existing yeast?


The above is the microbiologist in me speaking. I am not a yeast expert at all, so I'm not sure specifically what allows yeast to tolerate other yeast or not... may be worth looking into? Microbiology is fascinating!
My wife works for the U of A, and while she is employed by them I have the ability pay only $25/semester tuition, but it means quitting my job simply because my work schedule would not allow it, and my work is not flexible at all with my schedule. I am considering it though, and ironically, microbiology is the area of study that I would pursue. I know they say it is never too late to go back to school, however, I am 33 and we have our first child on the way maybe some things aren't meant to be.

Microbiology sounds fascinating at the least!
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