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Old 01-06-2011, 08:21 PM   #1
OldManHouston
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Default Yeast Harvesting Gravity Limits

So I've harvested a few batches of yeast from lower gravity brews (<1.060) at this point. Now I'm wondering, if you pitch the proper amount of yeast in the first place at what gravity does it become not such a good idea to harvest the yeast from a batch? I would think that if the proper amount of yeast is pitched, you could harvest off beers of 1.070 but I'm no yeast expert. That being said, I wouldn't consider harvesting off a brew that started much higher than 1.070. I know brewers yeast is alcohol tolerant but has it limits.

Most of my brews are in the 1.060 - 1.075 range and would like to know whether harvesting from these is a good idea or not.

Apologies if this has been discussed already but my searches weren't coming up with much.



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Old 01-06-2011, 08:47 PM   #2
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Generally lower gravity lower hops equals best viability. At those gravity ranges it isn't ideal, but you probably would get away with a repitch, where it will really impact things is asking them to go multiple generations in that environment.



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Old 01-07-2011, 12:16 AM   #3
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where it will really impact things is asking them to go multiple generations in that environment.
Not quite sure I would agree with this idea, if the yeast have survived(actually thirived) the fermentation process once, why can't they do it again?

In a higher gravity beer you will just a larger yeast population, they work just as normal.
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Old 01-07-2011, 01:06 AM   #4
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You start to stress the yeast and they start mutating. Repeated use will eventually change the yeast properties.

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Old 01-07-2011, 02:22 AM   #5
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You start to stress the yeast and they start mutating. Repeated use will eventually change the yeast properties.
No doubt that stressed yeast and repeated use will change the yeast. That is the reason I understand you generally do not want to harvest yeast past 5 or so generations.

My real question are what the general safe gravity levels are for harvesting. Maybe harvesting from a 1.065 beer is only good to reuse once instead of 5 times?? Maybe it's not good to harvest at all...
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Old 01-07-2011, 02:31 AM   #6
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Seriously, this whole mutation thing has gone way out of control. It is not an issue. Don't wash your yeast if you are that concerned about it, but there is no REAL evidence of yeast mutation having any effect on the finished product.

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Old 01-07-2011, 01:22 PM   #7
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I've heard around 5%ABV is approaching the max.

I disagree with theredben. Yes, you can still make beer with yeast from stronger batches, but can you make the best beer possible? If Chris White and Jamil say that the yeast are not optimal, I believe them.

Probably the phrase I hate to hear more than anything on HBT is "it worked for me." Of course it worked for you! Yeast are incredibly resilient. They will almost definitely convert sugar to alcohol no matter how you treat them. It's the diminishing returns we have to be concerned about. If someone just wants to make beer that's just good enough, then you can definitely relax your standards on repitching yeast. But I know that most of us are chasing the holy grail of the perfect beer.

How much more excited are you about your beer when they turn out amazing versus really good? Yeast is just one of those factors to achieving that.

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Old 01-07-2011, 02:11 PM   #8
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Seriously, this whole mutation thing has gone way out of control. It is not an issue. Don't wash your yeast if you are that concerned about it, but there is no REAL evidence of yeast mutation having any effect on the finished product.
As you repitch yeast you increase the amount of respiratory deficient mutants and at the same time there is a diminishing ability to reduce diacetyl. This suggests a correlation between the mutants and diacetyl issues (which cannot completely rule out the potential for gram positive bacteria being an issue here) according to George Fix based on research on lager yeast. As well, there are flocculation issues contributed to mutants.
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Old 01-07-2011, 02:30 PM   #9
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Not quite sure I would agree with this idea, if the yeast have survived(actually thirived) the fermentation process once, why can't they do it again?

In a higher gravity beer you will just a larger yeast population, they work just as normal.
Wyeast says so...they do not thrive in the high osmotic pressure of high gravity brews nor do they thrive in the high alcohol. Just because they can doesnt mean its good for them.

Think of it like this, its winter of 1944 and the 101st Airborne is surrounding Bastogne in its defense, its food, medical, and ammo are running low and the Germans are pushing hard to take the city. The 101st gave everything and stopped the Germans dead. When all was said and done many were dead and the rest are injured and exhausted. Now you have a choice, do you want those boys in that condition marching into Berlin? Or do you want a rested and equipped soldiers moving into Berlin?
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Old 01-07-2011, 02:33 PM   #10
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Originally Posted by Bensiff View Post
Generally lower gravity lower hops equals best viability. At those gravity ranges it isn't ideal, but you probably would get away with a repitch, where it will really impact things is asking them to go multiple generations in that environment.
I've heard someone on here mention hops ruining yeast viability before and I'm curious. Is that really true (to me it doesn't make any sense)? Why? Any references? I understand the lower gravity deal.


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