Author Topic: 90% viability necessary? Desirable? Unnecessary?  (Read 1168 times)

Offline nateo

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90% viability necessary? Desirable? Unnecessary?
« on: September 17, 2011, 01:49:42 PM »
I've been re-reading White and Zainasheff's Yeast book, and they mention more than a few times how you should only use yeast if the viability is over 90%. From the MrMalty calculator, it looks like liquid yeast would have to be made within 10 days of your use to have 90% viability.

So, my question is, for people who brew a lot of the same recipes of beer with the same yeast, have you noticed any difference in the finished beer if your yeast was one week old, rather than two weeks old, or three weeks?

I've used yeast that's pretty old. I recently used some yeast made in April, and the beer turned out fine. Maybe it could have been better with fresher yeast, but I'm curious how much of a difference it actually makes.

I wonder if they're just talking about direct pitching without making a starter?
« Last Edit: September 17, 2011, 01:51:40 PM by nateo »
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Offline a10t2

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #1 on: September 17, 2011, 04:23:57 PM »
So, my question is, for people who brew a lot of the same recipes of beer with the same yeast, have you noticed any difference in the finished beer if your yeast was one week old, rather than two weeks old, or three weeks?

I've pitched yeast with (methylene blue) viabilities as low as 71% and as high as 98%, and can't tell any difference in the beers as long as I adjust the pitching rate accordingly. I brew each recipe, on average, every 10 days or so, so I'd like to think I'd pick up on those minor variations, but of course it could just be that I can't taste whatever it is that would differentiate them. FWIW, this is all with US-05 and Wyeast 1318.
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Offline dhacker

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #2 on: September 17, 2011, 04:26:43 PM »
II wonder if they're just talking about direct pitching without making a starter?

Has to be . . it would be impossible to obtain 90% viability otherwise and LHBS' couldn't stock it for any length of time.
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Offline nateo

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #3 on: September 18, 2011, 07:04:22 AM »
a10t2 - Great info. That's exactly what I was looking for.

dhacker - I've always wondered why Wyeast says that one of their packages will directly inoculate 5 gallons of wort with "professional pitching rates." Following their advice I made some pretty "meh" beers when I was starting out. By their own calculations for pitching rate (from their website: OG  <1.060 - 6m/ml) you would need 120b for a 20L batch.
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Offline james

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #4 on: September 18, 2011, 08:19:34 AM »
I've pitched yeast with (methylene blue) viabilities as low as 71% and as high as 98%, and can't tell any difference in the beers as long as I adjust the pitching rate accordingly. I brew each recipe, on average, every 10 days or so, so I'd like to think I'd pick up on those minor variations, but of course it could just be that I can't taste whatever it is that would differentiate them. FWIW, this is all with US-05 and Wyeast 1318.

I recall reading that methylene blue was unreliable for viability below 80% though I can't remember the exact reasons and another dye was more accurate at lower levels (maybe violet?)

I'm sure experience in your case is a big factor and you know your yeast and how the brews taste in the end.

Offline a10t2

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #5 on: September 18, 2011, 08:51:28 AM »
I recall reading that methylene blue was unreliable for viability below 80%

I've heard that as well, though I'm not sure I believe it. The viabilities I get are both repeatable and correlate well with the rules of thumb out there for viability reduction over time.
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Offline james

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #6 on: September 18, 2011, 09:03:17 AM »
I recall reading that methylene blue was unreliable for viability below 80%

I've heard that as well, though I'm not sure I believe it. The viabilities I get are both repeatable and correlate well with the rules of thumb out there for viability reduction over time.

Maybe it is only a slight deviation below 80% but when you get to 30-50% it can be wildly inaccurate, I don't know enough about it to know where the supposed error occurs.

Like I said though experience and knowing your yeast and brew are a major factor in this case. 

Offline nateo

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Re: 90% viability necessary? Desirable? Unnecessary?
« Reply #7 on: September 18, 2011, 09:03:30 AM »
I recall reading that methylene blue was unreliable for viability below 80% though I can't remember the exact reasons and another dye was more accurate at lower levels (maybe violet?)

In "Yeast" they talk about methylene violet as an alternative that may be more reliable. I believe the issue is that the cells can be stained either because they're dead, or they're too weak to effectively resist the dye, or pump out the dye if it does enter their membrane. In practical terms though, if the cell is that weak, wouldn't it basically have the same fermentation performance (vitality) as a dead cell?
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