Author Topic: Help be interpret this  (Read 1251 times)

Offline denny

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Help be interpret this
« on: June 06, 2018, 10:12:50 PM »
Back in 2003, the Homebrew Digest ran "A Fortnight of Yeast", where you could ask questions of Dr. Clayton Cone, head of Lallemand and inventor of Fermaid K.  Here's the question I asked and Dr. Cone's response....

"Dr. Cone,
   First, thank you so much for giving us some of your time.
   My question concerns yeast growth as it relates to flavors in beer.  I
have read several articles mentioning that yeast growth is important to
flavor production in beer, and that the amount of yeast growth is related to
the amount of yeast pitched.  My own completely unscientific experiments
have
lead  me to believe that I produce more "interesting' beers when I, for
instance, repitch only part of the yeast slurry from a previous batch
rather than the entire amount.  The conventional wisdom in the homebrew
world seems to be to use the entire previous slurry to produce short lag
times.  Is there a relationship between yeast growth and the flavors
produced in beer?  Is it better to pitch an entire previous yeast slurry,
or is there a benefit to using a large, but not entire, amount of
slurry?  I apologize for the vagueness of the question, but I have no way
to quantify the exact amounts I've been using.  It's simply either "all" or
"part".
   Thank you again.
Denny Conn


Denny Conn,
   Ester and other flavor component production or synthesis is a complex
subject because there are so many variables taking place at the same time.
   You are right, ester production is related to yeast growth but not in the
way you might think. The key element to yeast growth and ester production is
acyl Co-A. It is necessary for both yeast growth and ester production.  When
it is busy with yeast growth, during the early part of the fermentation, it
is not available for ester production.  Ester production is directly related
to biomass production. Everything that increases biomass production
(intensive aeration, sufficient amount of unsaturated fatty acids,
stirring) decreases ester production. The more biomass that is produced the
more Co-enzyme A is used and therefore not available for ester production.
Anything that inhibits or slows down yeast growth usually causes an increase
in ester production: low nutrient, low O2.  It has been noted that a drop in
available O2 from 8 ppm down to 3 ppm can cause a four fold increase in
esters.
   Stirring in normal gravity decreases ester production. Stirring in high
gravity increases ester production. CO2 pressure in early fermentation
decreases ester production.  Taller fermenters produce less esters than
short fermenters. High temperature early in fermentation decreases ester
production.  High temperature later in fermentation increases ester
production. Low pitching rate can result in less esters.
   There are other flavor components such as higher alcohol that have there
own
set of variables. Stirring increases production of higher alcohols.  CO2
pressure does not effect the production of alcohol. Amino acid levels in the
wort effect the production of higher alcohols.  Most of the higher alcohol
is produced during the growth phase (exponential phase) of the yeast.
   I am sure that there are many other variables.  I am also sure that there
are beer makers that have experienced the very opposite with each of the
variables.

   Pitching rates depend on several factors:
   (1) The speed in which you wish the fermentation to take place.  Some
professional brew master are in more of a hurry than others; desired beer
style, shortage of fermenter space.  Pitching rates would vary as a means to
increase or decrease the total fermentation time. 10 X 10/6th cell
population for normal fermentation rates.  20 X 10/6th or more for a quick
turn around.
   (2) Temperature control.  If lack of refrigeration is a problem, the
fermentation needs to be spread out over a longer period  by pitching with
less yeast.
   (3) Health of the pitching yeast. If the pitching yeast has not been
stored
under ideal conditions (4C for less than one week) then larger pitching rate
must be done to compensate for the deteriorate of the yeast.  Increased
pitching rates has its limits in trying to compensate for poor storage
conditions.
   (4) When all other variables are under control you can use variations in
pitching rates to achieve certain flavor profile that are of interest to
you.
   Conventional wisdom regarding pitching rate can lead to problems.  During
each fermentation cycle the yeast will increase in size about three times,
so if you use all the yeast from the previous batch you will soon be
pitching with a huge amount of yeast.  Professional brewers usually re-pitch
with about 25% of the yeast from the previous batch.
   Proper handling of the yeast during storage (4C and <7 days) will
minimize
any problem with long lag phase. Start with a fresh culture of yeast after
about five recycles for bacteria control and or after 10 - 15 cycles for
genetic drift purposes.
   There are many who will say that they are proud of the fact that they
have
used the same yeast after over 100 cycles.  More power to them. I wish that
I could explain their luck. Good practices suggest frequent renewal with a
fresh culture is a good policy.
   Thank you for your very good question.

Clayton Cone"

OK, so I've always taken that to mean that pitching "too much" yeast means that there is less biomass production and consequently more esters.  That's pretty much the opposite of the conventional wisdom, as MANY people have pointed out to me over the years.  So, I want to know how you interpret this.  Am I right?  Or am I totally missing something that confirms the conventional wisdom?
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Offline dmtaylor

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Re: Help be interpret this
« Reply #1 on: June 07, 2018, 01:25:21 AM »
Your interpretation of Dr. Cone's theory appears correct.  Dr. Cone's theories, however, deserve more testing.  I honestly don't know what to think until I test it some more.
Dave

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Offline RC

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Re: Help be interpret this
« Reply #2 on: June 07, 2018, 05:42:42 AM »
I too think that your interpretation of Dr. Cone's response is correct. If the acylCoA is not being used for the production of new cells, it is "freed up" to take part in the production of esters. Hence, overpitching = less yeast growth = more ester production.

If he's correct, then as far as the conventional wisdom, that overpitching results in fewer esters (which is definitely consistent with my experience), here's a hypothesis. By overpitching, the yeast will reach their maximum cell density more quickly, thus spending less time in the growth phase. Even though esters are being produced in greater abundance relative to the growth rate, the time spent in the growth phase is too short to allow the esters to accumulate much, such that the absolute production of esters is less, compared to a lower pitch rate in the same wort. So even though overpitching "stimulates" ester production, it still leads to less ester production overall simply because there is less time spent in the growth phase.

Offline ynotbrusum

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Re: Help be interpret this
« Reply #3 on: June 07, 2018, 11:48:01 AM »
I too think that your interpretation of Dr. Cone's response is correct. If the acylCoA is not being used for the production of new cells, it is "freed up" to take part in the production of esters. Hence, overpitching = less yeast growth = more ester production.

If he's correct, then as far as the conventional wisdom, that overpitching results in fewer esters (which is definitely consistent with my experience), here's a hypothesis. By overpitching, the yeast will reach their maximum cell density more quickly, thus spending less time in the growth phase. Even though esters are being produced in greater abundance relative to the growth rate, the time spent in the growth phase is too short to allow the esters to accumulate much, such that the absolute production of esters is less, compared to a lower pitch rate in the same wort. So even though overpitching "stimulates" ester production, it still leads to less ester production overall simply because there is less time spent in the growth phase.

This has been my experience as well.  I didn’t know for sure, but I suspected the limited growth affected the ester compounds in terms of total output overall.

I also wonder if the yeast consume (in effect) some portion of the ester compounds that are initially produced....but I have no science on that.
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Offline denny

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Re: Help be interpret this
« Reply #4 on: June 07, 2018, 03:15:02 PM »
Your interpretation of Dr. Cone's theory appears correct.  Dr. Cone's theories, however, deserve more testing.  I honestly don't know what to think until I test it some more.

Remember, Dr. cone was no slouch.  I've been working on his advice for 15 years and find it right on.
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Offline Big Monk

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Re: Help be interpret this
« Reply #5 on: June 07, 2018, 03:56:02 PM »
Your interpretation of Dr. Cone's theory appears correct.  Dr. Cone's theories, however, deserve more testing.  I honestly don't know what to think until I test it some more.

Remember, Dr. cone was no slouch.  I've been working on his advice for 15 years and find it right on.

We should be clear here so that people reading this don't get the wrong idea: the stuff Dr. Cone proposes is not theory. It's well established and well studied microbiology. We shouldn't entertain the idea that this is something that requires testing to be proved right.

Maybe testing to see how it applies to each individual, but certainly not testing to validate.

We have the Macro-Lager industry to thank for most of what we know about ester and higher alcohol formation and synthesis.
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Offline denny

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Re: Help be interpret this
« Reply #6 on: June 07, 2018, 04:02:00 PM »
We should be clear here so that people reading this don't get the wrong idea: the stuff Dr. Cone proposes is not theory. It's well established and well studied microbiology. We shouldn't entertain the idea that this is something that requires testing to be proved right.

Maybe testing to see how it applies to each individual, but certainly not testing to validate.

We have the Macro-Lager industry to thank for most of what we know about ester and higher alcohol formation and synthesis.

Absolutely.  I was gonna mention that in response to Dave but I got involved with something and spaced it.
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Online klickitat jim

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Re: Help be interpret this
« Reply #7 on: June 07, 2018, 04:23:04 PM »
Another question is what low growth is doing to residual FAN numbers, and therefore final pH of your beer, and therefore feed and safety zone for contamination to reproduce.

Residual FAN is another reason to be a "fan" of pitching active starters to low FAN euro malts, rather than pitching high cell counts to high DP, high FAN American malts.

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Re: Help be interpret this
« Reply #8 on: June 07, 2018, 06:37:52 PM »
   I am sure that there are many other variables.  I am also sure that there
are beer makers that have experienced the very opposite with each of the
variables.

...   There are many who will say that they are proud of the fact that they
have
used the same yeast after over 100 cycles.  More power to them. I wish that
I could explain their luck. Good practices suggest frequent renewal with a
fresh culture is a good policy.
   

I rarely re-pitch over a couple times anymore, for any noumber of reasons, the first of which is limiting contamination and the second is genetic drift concerns (despite taking a clean lager yeast out to 25 generations over a couple years without problems, just to see what happens).  I now routinely use the SNS approach and get very good results with what might be considered underpitching slightly.

So, I agree with Dr. Cone, but have experienced results that might be considered contradictory to what one might conclude from his response to your inquiry.  In the end, these yeast microbes are incredibly complex and subtle creatures and they have remarkable abilities to overcome or "heal" what we brewers put them through, whether intentionally or accidentally done.

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Re: Help be interpret this
« Reply #9 on: June 07, 2018, 08:10:50 PM »
Incoming anecdote: I brewed a batch of pale ale a couple weeks ago and managed to fat-finger something (maybe literally by having my finger on the scale) so I had just over half the yeast I needed, and didn't realize it until I had pitched the first fermenter. So the second got pitched at 0.18 M/mL-°P, which has to be the lowest I've ever done.

It took substantially longer to reach FG (day 9 instead of 6), so there's that. I tapped it for a party last night, and it's a little off, but not in the way I'd necessarily expect. It's dry and bitter without much if any yeast character, very West Coast-style. Not even terrible, just not what I wanted, and not nearly as much ester character as the "normal" fermenter (which also got 1272 at 0.77 M/mL-°P).
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Offline dmtaylor

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Re: Help be interpret this
« Reply #10 on: June 07, 2018, 08:48:38 PM »
Your interpretation of Dr. Cone's theory appears correct.  Dr. Cone's theories, however, deserve more testing.  I honestly don't know what to think until I test it some more.

Remember, Dr. cone was no slouch.  I've been working on his advice for 15 years and find it right on.

We should be clear here so that people reading this don't get the wrong idea: the stuff Dr. Cone proposes is not theory. It's well established and well studied microbiology. We shouldn't entertain the idea that this is something that requires testing to be proved right.

Maybe testing to see how it applies to each individual, but certainly not testing to validate.

We have the Macro-Lager industry to thank for most of what we know about ester and higher alcohol formation and synthesis.

I don't remember.  I never heard of Dr. Cone.  Could be Dr. Seuss for all I knew.  Guess I should look him up sometime.

Regardless, there are few humans in which I would place blind faith, regardless of whether they are doctors or scholars or wrote books or whatever.  They may be right about a lot of stuff, maybe even everything.  But who really knows.

I'll look him up sometime.  But I am not spending much time online this month.  Maybe July.
Dave

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Offline Big Monk

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Re: Help be interpret this
« Reply #11 on: June 07, 2018, 09:02:51 PM »
Your interpretation of Dr. Cone's theory appears correct.  Dr. Cone's theories, however, deserve more testing.  I honestly don't know what to think until I test it some more.

Remember, Dr. cone was no slouch.  I've been working on his advice for 15 years and find it right on.

We should be clear here so that people reading this don't get the wrong idea: the stuff Dr. Cone proposes is not theory. It's well established and well studied microbiology. We shouldn't entertain the idea that this is something that requires testing to be proved right.

Maybe testing to see how it applies to each individual, but certainly not testing to validate.

We have the Macro-Lager industry to thank for most of what we know about ester and higher alcohol formation and synthesis.

I don't remember.  I never heard of Dr. Cone.  Could be Dr. Seuss for all I knew.  Guess I should look him up sometime.

Regardless, there are few humans in which I would place blind faith, regardless of whether they are doctors or scholars or wrote books or whatever.  They may be right about a lot of stuff, maybe even everything.  But who really knows.

I'll look him up sometime.  But I am not spending much time online this month.  Maybe July.

The point isn’t to take Dr. Cone on blind faith. It’s that the science is settled on this.

It’s the application of the science that will differ from person to person and require testing, not the scientific backbone.
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Offline Joe Sr.

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Re: Help be interpret this
« Reply #12 on: June 07, 2018, 09:05:01 PM »
I think you're interpreting correctly what he says, but he also qualifies it with this statement:

"I am sure that there are many other variables.  I am also sure that there
are beer makers that have experienced the very opposite with each of the
variables."

Which I take to be a sort of YMMV statement.

My guess as to what's going on with the conventional wisdom is similar to what others have stated here.  With an overpitch (particularly a full yeast cake) your fermentation goes super quick, so there is less time for ester production and possibly fewer esters overall though perhaps produced at a quicker rate during the time they were produced.  Also, I would expect that it is a hotter fermentation, which Dr. Cone notes will depress ester production.

But there are a lot of variables and your experience may differ...
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Offline Big Monk

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Re: Help be interpret this
« Reply #13 on: June 07, 2018, 09:38:19 PM »
I think you're interpreting correctly what he says, but he also qualifies it with this statement:

"I am sure that there are many other variables.  I am also sure that there
are beer makers that have experienced the very opposite with each of the
variables."

Which I take to be a sort of YMMV statement.

My guess as to what's going on with the conventional wisdom is similar to what others have stated here.  With an overpitch (particularly a full yeast cake) your fermentation goes super quick, so there is less time for ester production and possibly fewer esters overall though perhaps produced at a quicker rate during the time they were produced.  Also, I would expect that it is a hotter fermentation, which Dr. Cone notes will depress ester production.

But there are a lot of variables and your experience may differ...

If you aren’t counting cells then there will be wild variation between brewers.

Accurate cell counts and viability checks are a pre-requisite to any non-circumstantial qualifying statement about yeast performance.

This is an often overlooked factor with homebrewers that try and apply scientific concepts to yeast management.

With that said, I certainly don’t want to discount anyone’s anecdotal evidence of success without cell counting. Plenty of people don’t count and are successful brewers. I just want to point out that yeast experiments at the academic and professional level are always carried out with a definite knowledge of how many cells they have and how healthy they are. This makes the results more meaningful and definitive. 

Do you guys remember the section on yeast from BLAM? Stan references Greg Casey’s presentations from the Rocky Mountain Micro Brewing Symposium there and in Brewing with Wheat. I reached out to Greg though LinkedIn and he sent me his presentations from 2004, 2005 and 2006. They are revelation as far as yeast management is concerned.
« Last Edit: June 07, 2018, 09:55:30 PM by Big Monk »
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Offline Joe Sr.

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Re: Help be interpret this
« Reply #14 on: June 07, 2018, 10:11:09 PM »
I am not a scientist, but I don't think you need to count cells to know that there is a significant difference between pitching a full yeast cake from a previous batch and pitching a smack pack.

I'm not crapping on the science, but I think that when you're dealing with orders of magnitude scientific precision may not always be needed.  Also, when you're talking about repeated results (over pitch, lower esters) across a span of years and many different brewers it's fair to question what's going on when results appear to differ from the science.

We're all speculating here anyway.
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