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Author Topic: Yeast Color  (Read 2645 times)

Offline Bel Air Brewing

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Yeast Color
« on: November 14, 2020, 08:15:34 am »
In the past my harvested yeasts were always a light peanut-butter color. I have noticed that my W-34/70 yeast (8th gen) has turned a grayish color while in storage.

My Kolsch yeast (Wyeast - 3rd gen) has a slight purple tint to it.

Are these colors telling me the yeast has problems? The aroma from the storage bottle is still Ok.

Offline majorvices

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Re: Yeast Color
« Reply #1 on: November 14, 2020, 09:05:40 am »
Purplish is weird. But I wouldn't entirely rely on color but, that said, creamy, pale colored slurries are always the best. I always use my slurries within a couple of weeks or start fresh.

Offline majorvices

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Re: Yeast Color
« Reply #2 on: November 14, 2020, 09:08:13 am »
Not sure if you used wheat in the kölsch yeast but Best Wheat malt always left behind a weird purple color when draining the mashtun

Offline Bel Air Brewing

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Re: Yeast Color
« Reply #3 on: November 14, 2020, 09:17:44 am »
Yes, creamy pale color is what I am accustomed to.
Just wondering about the grayish tint that is now prevalent in the yeast?

Might just start fresh and not take any chances.

Offline Saccharomyces

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Re: Yeast Color
« Reply #4 on: November 14, 2020, 09:40:15 am »
The color change is due to your practice of serial overpitching.  Yeast cells turn gray as they become non-viable.   Overpitching causes a culture to become progressively older with each successive re-pitch due to suppression of new growth. If you want your cultures to last more than a couple of repitches, you may want to start pitching between 150 and 175ml of thick slurry per 5 gallons in the future.  Garrett Oliver was the first pro-brewer I heard mention that overpitching is a bad practice. He also mentioned that he frequently underpitches to reduce the average age of the cells in his pitching yeast.  That was back in the 90s.

Offline Bel Air Brewing

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Re: Yeast Color
« Reply #5 on: November 14, 2020, 10:28:38 am »
The color change is due to your practice of serial overpitching.  Yeast cells turn gray as they become non-viable.   Overpitching causes a culture to become progressively older with each successive re-pitch due to suppression of new growth. If you want your cultures to last more than a couple of repitches, you may want to start pitching between 150 and 175ml of thick slurry per 5 gallons in the future.  Garrett Oliver was the first pro-brewer I heard mention that overpitching is a bad practice. He also mentioned that he frequently underpitches to reduce the average age of the cells in his pitching yeast.  That was back in the 90s.

Over pitching? Yes, probably so. But the beers have always been extremely good, with no signs of negative issues resulting from the quantity of yeast. I'll cut back on the yeast amount going forward, and see what effect this has on the beer, and the yeast that is harvested.

Offline Saccharomyces

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Re: Yeast Color
« Reply #6 on: November 15, 2020, 06:48:07 am »
Over pitching? Yes, probably so. But the beers have always been extremely good, with no signs of negative issues resulting from the quantity of yeast. I'll cut back on the yeast amount going forward, and see what effect this has on the beer, and the yeast that is harvested.

That practice is not about beer flavor.  It is about maintaining culture viability.  People routinely dump new wort onto an old yeast cake.  Does it work? Absolutley!  Is is a bad practice if one serially repitches? Absolutely!  A yeast culture needs to go through four to five replication periods per fermentation in order to keep the culture from becoming mostly non-viable cells. You do not have to take my word in it.  Here is an answer on White Labs' website : https://www.whitelabs.com/faq/brewing/overpitching-yeast-harmful

Offline Bel Air Brewing

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Re: Yeast Color
« Reply #7 on: November 15, 2020, 10:10:52 am »

Offline chinaski

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Re: Yeast Color
« Reply #8 on: November 16, 2020, 05:35:17 pm »
Without reading the links- is the take-home message that pitching the correct number of cells about having those pitched cell go through a population growth phase first (producing new cells)?  Over pitching eliminates the growth phase and so the pitched cells go directly to fermentation?

Do I have that right?

Over pitching? Yes, probably so. But the beers have always been extremely good, with no signs of negative issues resulting from the quantity of yeast. I'll cut back on the yeast amount going forward, and see what effect this has on the beer, and the yeast that is harvested.

That practice is not about beer flavor.  It is about maintaining culture viability.  People routinely dump new wort onto an old yeast cake.  Does it work? Absolutley!  Is is a bad practice if one serially repitches? Absolutely!  A yeast culture needs to go through four to five replication periods per fermentation in order to keep the culture from becoming mostly non-viable cells. You do not have to take my word in it.  Here is an answer on White Labs' website : https://www.whitelabs.com/faq/brewing/overpitching-yeast-harmful

Offline denny

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Re: Yeast Color
« Reply #9 on: November 17, 2020, 08:12:43 am »
Without reading the links- is the take-home message that pitching the correct number of cells about having those pitched cell go through a population growth phase first (producing new cells)?  Over pitching eliminates the growth phase and so the pitched cells go directly to fermentation?

Do I have that right?

Over pitching? Yes, probably so. But the beers have always been extremely good, with no signs of negative issues resulting from the quantity of yeast. I'll cut back on the yeast amount going forward, and see what effect this has on the beer, and the yeast that is harvested.

That practice is not about beer flavor.  It is about maintaining culture viability.  People routinely dump new wort onto an old yeast cake.  Does it work? Absolutley!  Is is a bad practice if one serially repitches? Absolutely!  A yeast culture needs to go through four to five replication periods per fermentation in order to keep the culture from becoming mostly non-viable cells. You do not have to take my word in it.  Here is an answer on White Labs' website : https://www.whitelabs.com/faq/brewing/overpitching-yeast-harmful

Yes, you are correct.  I discovered years ago through experimentation that I preferred the flavor of beer fermented with part of a slurry rather than the entire thing.
« Last Edit: November 17, 2020, 09:50:39 am by denny »
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Offline Bel Air Brewing

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Re: Yeast Color
« Reply #10 on: November 17, 2020, 09:34:15 am »
Does yeast not always go through an initial acclimation stage, where O2 is taken up, followed by a growth stage? Whether you under pitch, or over pitch? I always over pitch my lagers.

Offline denny

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Re: Yeast Color
« Reply #11 on: November 17, 2020, 09:50:20 am »
Does yeast not always go through an initial acclimation stage, where O2 is taken up, followed by a growth stage? Whether you under pitch, or over pitch? I always over pitch my lagers.

It is my understanding that if you overpitch yeas5 will go through fewer growth cycles, which can have a negative effect on flavor.  That has also been my observation based on experience.
Life begins at 60.....1.060, that is!

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Offline Bel Air Brewing

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Re: Yeast Color
« Reply #12 on: November 17, 2020, 10:15:30 am »
Does yeast not always go through an initial acclimation stage, where O2 is taken up, followed by a growth stage? Whether you under pitch, or over pitch? I always over pitch my lagers.

It is my understanding that if you overpitch yeas5 will go through fewer growth cycles, which can have a negative effect on flavor.  That has also been my observation based on experience.

Please define growth cycles. Is this a single cycle, or growth phase, or are there multiple cycles / growth phases involved?

How many cycles will a standard pitching rate experience, and how many fewer cycles will an over pitched yeast experience?

Has anyone done A-B taste tests to confirm the results and flavor impact?

Here is what I found on Brulosophy...

https://brulosophy.com/2016/11/07/yeast-pitch-rate-pt-5-underpitch-vs-overpitch-in-a-lager-exbeeriment-results/
« Last Edit: November 17, 2020, 10:19:54 am by TXFlyGuy »

Offline denny

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Re: Yeast Color
« Reply #13 on: November 17, 2020, 10:27:38 am »
Does yeast not always go through an initial acclimation stage, where O2 is taken up, followed by a growth stage? Whether you under pitch, or over pitch? I always over pitch my lagers.

It is my understanding that if you overpitch yeas5 will go through fewer growth cycles, which can have a negative effect on flavor.  That has also been my observation based on experience.

Please define growth cycles. Is this a single cycle, or growth phase, or are there multiple cycles / growth phases involved?

How many cycles will a standard pitching rate experience, and how many fewer cycles will an over pitched yeast experience?

Has anyone done A-B taste tests to confirm the results and flavor impact?

Here is what I found on Brulosophy...

https://brulosophy.com/2016/11/07/yeast-pitch-rate-pt-5-underpitch-vs-overpitch-in-a-lager-exbeeriment-results/

I'm talking about 4-5 cycles of cell replication.  Now, I'm now watching with a microscope to see what they're doing.  I just know that my experiwnce is that fewer is better, as long as it's not too few.  Close enough for me.  Mark might have numbers, but as Chris White said to Drew and me "homebrewers are too hung up on numbers."  For me, the beer tells the story.  In terms of Brulosophy experiments,  theyre interesting data points but not conclusions.  Data points from you or me are equally valid.
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Offline Saccharomyces

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Re: Yeast Color
« Reply #14 on: November 17, 2020, 12:57:12 pm »
A yeast culture will almost always experience a lag phase where it consumes O2 and builds ergosterol and unsaturated fatty acid reserves.  What differs is the number of replication periods it takes to reach maximum cell density when one overpitches. 


Let's start with the math. Nineteen liters (five gallons) of wort has a maximum cell density of approximately 200,000,000,000 * 19 = 3.8 trillion cells. 

Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 200 billion
Replication_Periods = log(3800 / 200) / log(2) =  log(19) / log(2) = 4.25 replication periods

Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 400 billion
Replication_Periods = log(3800 / 400) / log(2) =  log(9.5) / log(2) = 3.25 replication periods

Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 800 billion
Replication_Periods = log(3800 / 800) / log(2) =  log(4.75) / log(2) = 2.25 replication periods

Batch size = 19L
Batch_Maximum_Cell_Density = 19 * 200,000,000,000 = 3.8 trillion
Pitched_Cell_Count = 1.6 billion
Replication_Periods = log(3.8 / 1.6) / log(2) =  log(2.375) / log(2) = 1.25 replication periods

As one can see, doubling the pitch rate reduces the replication period count by one.

How do these pitched cell counts translate to thick slurry?  The generally accepted cell count per milliliter of thick slurry is 1.2 billion cells.

Pitch_200_Billion_Cells = 200 / 1.2 = 167ml

Pitch_400_Billion_Cells = 400 / 1.2 = 334ml

Pitch_800_Billion_Cells = 800 / 1.2 = 667ml

Pitch_1600_Billion_Cells = 1600 / 1.2 = 1334ml

If we follow the standard practice of cropping from the middle of the cake, we have mostly new cells with a pitch rate of 200B cells.  The new cell count is reduced slightly with a pitching rate of 400B cells.  However, after we get to 800B cells, we are looking at a minimum of 21% old cells even if we crop perfectly.  By the time we get to 1.6T cells, half of the cropped cells are old.  Old yeast cells are susceptible to the build up of something known as reactive oxygen species (ROS).  ROS can cause damage to DNA and RNA, not to mention cell death.

« Last Edit: November 18, 2020, 06:24:25 am by Saccharomyces »