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HOMEBREW Digest #4328
HOMEBREW Digest #4328 Thu 21 August 2003
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
Digest Janitor: janitor@hbd.org
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Contents:
Aluminum vs Steel tanks (John Palmer)
flashlights and beer (Bob Devine)
Re: Do levels (Cairns Jim MTPROUS)
Sanitizers and Septic (rickdude02)
Gump and knowing it all ("Dave Burley")
How much priming sugar per bottle (Bob Pelletier)
Re: Dried Hops ("Jerry Zeidler")
Exploding CO2 tanks ("Keith Lemcke")
Re: Sanitizers and Septic ("Rob Dewhirst")
Starter Strategies ("Martin Brungard")
RE: anti-foam (Brian Lundeen)
Re: Munton's Wheat DME (Robert Sandefer)
Dr. Cone Responds-Conical Fermenters & Harvesting Yeast- Bob Fawbush ("Rob Moline")
Dr. Cone Responds-Metabolism (follow up)-Fredrik ("Rob Moline")
Dr. Cone Responds - Aerobic yeast starters- Fred L Johnson ("Rob Moline")
Dr. Cone Responds - Attenuation- Dave ("Rob Moline")
CO2 Tanks ("Tanksalot")
Re: The reason for the seemingly excessive oxygen requirements? ("-S")
* * * * * * * * * * * * * * * * * * * * * * * * * * * * *
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* * * * * * * * IN PROGRESS! * * * * * * * *
* Dr. Clayton Cone Fortnight of Yeast *
* 8/11/03 - 8/22/03 Yeast Questions Answered *
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Date: Tue, 19 Aug 2003 21:56:58 -0700
From: John Palmer <jjpalmer@altrionet.com>
Subject: Aluminum vs Steel tanks
Sorry, I missed the earlier question, just saw Rama's reply today. The
thought seems to be that aluminum tanks are more dangerous or prone to
failure than steel tanks, and the reason given was that aluminum was
more brittle than steel. Mostly true.
This is a bit of a trick question, it's like picking any dog to fight
any cat, ie. the outcome is going to depend on the breed. Same with the
aluminum and steel alloys.
Pure aluminum is much more ductile than iron or steel, but it is much
weaker too. To make a tank out of aluminum, you have to alloy it with
magnesium, silicon, mangenese, etc. to bring the strength up, and in
the forming process you cold work it a lot to raise the strength even
more, and yes it does get more brittle. Meanwhile, plain carbon steel
is so cheap that you can afford to make a heavy tank out of it. I
should also mention that tanks are designed to Leak-before-Burst, i.e.,
they shouldn't fail catastrophically if they develop a crack. Of course
if you shoot one with a bullet then all bets are off.
Carbon steel's perceived ductility and fatigue resistance has more to
do with the lack of alloying elements than the presence of carbon.
Aluminum, to achieve useful strengths, has more alloying elements to
stiffen the crystal structure, with the net result being that it work
hardens faster than carbon steel.
I am just scratching the surface here, but I have a feeling that I
would post more than anyone really cares about. One final thought is
that the fracture toughness of steel is higher than that of most
aluminum alloys, so that steel tanks can take more abuse than aluminum
tanks without failure.
John Palmer
john@howtobrew.com
www.realbeer.com/jjpalmer
www.howtobrew.com - the free online book of homebrewing
------------------------------
Date: Tue, 19 Aug 2003 23:40:53 -0600
From: Bob Devine <bob.devine@worldnet.att.net>
Subject: flashlights and beer
Eric <edahlber@rochester.rr.com> asks:
> Also, I know the phenomenon we call beer skunking is a result
> of light and hop oils reacting, but I am wondering if my nightly
> ritual of shining a flashlight into the carboy may be having any
> negative effect on my yeast? Photosensitive yeast?
Ahhh, the old Heisenbeer Uncertainty Principle. All homebrewers
go through this phase of checking on their beer to an, almost,
obsessive level. After all, if you aren't checking on the beer,
maybe it is not doing anything!
Seriously, the skunking effect comes from ultraviolet light
hitting and breaking isohumulones which, when combined with
hydrogen sulphide or other thiols, creates an organic compound,
mercaptan, that is detectable in the parts-per-billion level.
Unless your flashlight produces a lot of light in the ultra-violet
range (fluorescent lights do cause skunking), you should be safe.
But even if your flashlight produces only visible light, the
violet portion may cause skunking if a "sensitizer" such as
riboflavin causes more of the thiols to be formed.
Check back through the HBD archives for a paper reference.
Best to keep the fermenting beer in a dark spot.
Bob Devine
------------------------------
Date: Wed, 20 Aug 2003 09:53:19 -0400
From: Cairns Jim MTPROUS <Jim.Cairns@mt.com>
Subject: Re: Do levels
Date: Tue, 19 Aug 2003 12:20:27 +0000
From: "A.J. deLange" <ajdel@cox.net>
Subject: DO Levels
AJ wrote: I never really fully accepted the thesis that DO levels attainable
at a
particular partial pressure were a strong function of the strength of
the solution
Finally! A subject I know well. Lol
All DO meters measure O2 differently. However, the majority of them use a
Clark Polarographic cell and base the measurement on Henrys Law of Pressure.
Basically, Henries law states that the partial pressure of O2 in air should
be the same as in a liquid. But, it's a little more complicated than that.
There are many other factors that have to be accounted for to really
determine DO content. Temperature, salinity, membrane permeability, the
medium just to name a few. Plus, to cloud the measurement up just a little
more, all meters use the concentration curve of pure water. Keep in mind
most of these factors are for determining the concentration.(PPM/PPB)
Concentration is very difficult to determine. Saturation (0%-100%)
measurements are much more forgiving. Soooo...having said that, you're
right. There are a lot of factors that have to be taken into account in
order to make an accurate DO measurement. So many, that using this method is
not a practical way for determining the DO concentration of any given
medium.
Sincerely,
Jim C.
jim.cairns@mt.com
------------------------------
Date: Wed, 20 Aug 2003 06:44:42 -0400 (GMT)
From: rickdude02@earthlink.net
Subject: Sanitizers and Septic
Not to worry-- two factors prevent your use of sanitizers from
blocking proper operation of your septic tank.
The first is simply the sheer volume of water and waste that goes
into your tank as compared to the amount of sanitizer. IOW, the
sanitizer is too dilute to have an impact.
The second is that soil (sewage, waste, etc.) deactivates just
about any sanitizer, which is why you should always sanitize clean
items rather than dirty. (Acid based sanitizers can withstand the
deactivation, they just aren't that effective in penetrating soil.)
Rick Theiner
LOGIC, Inc.
------------------------------
Date: Wed, 20 Aug 2003 10:00:32 -0400
From: "Dave Burley" <Dave_Burley@charter.net>
Subject: Gump and knowing it all
Brewsters:
Gump says he refuses to call me to inform me that he doesn't know it all. At
least that's what I think he meant. {8< )
Keep on Brewin'
Dave Burley
------------------------------
Date: Wed, 20 Aug 2003 10:13:22 -0400
From: Bob Pelletier <rp@ihrsa.org>
Subject: How much priming sugar per bottle
I keg most of my beer but I need to bottle a few entries soon and was
wondering how much sugar I should add to each 12oz bottle. The beers are a
porter, a kolsch and a wheat. TIA, Bob
------------------------------
Date: Wed, 20 Aug 2003 13:31:51 -0400
From: "Jerry Zeidler" <gjzeidler@suscom.net>
Subject: Re: Dried Hops
David King wonders how others dry, package and store their homegrown hops.
When I harvest my hops, I lay the cones on a screen, which I lay on a
tabletop in a well-ventilated room with the shades drawn. It's not really
dark in there, but there's no direct sunlight hitting the cones. I allow the
hops to dry at ambient temperature for 24-36 hours, then turn them and
air-dry them for another 12-24 hours, or until the stems in the cones are
beginning to get brittle.
Once dry, I stuff 2 oz. into a sandwich-sized zipper-close baggie (takes
some squashing and cramming). I seal the baggie most of the way across, then
set the bag on a countertop and squash it further with a book or other
large, flat surface, then close the zipper seal with the weight still
bearing on the bag. This is to purge as much air out of the bag as possible.
Once sealed, I wrap the baggie in freezer wrap to prevent light exposure.
This double-wrapped package is then labeled with the type of hops and the
date packed, then placed in the chest freezer until brewing day.
I know that my method of "purging" air from the bags is imperfect, but I
have not had any reason to go to any further effort or expense, since my I
have always used my hops (or given them away) before they have had a chance
to go stale.
Jerry Zeidler
Williamsport, PA
------------------------------
Date: Thu, 21 Aug 2003 00:46:49 -0600
From: "Keith Lemcke" <klemcke@siebelinstitute.com>
Subject: Exploding CO2 tanks
Great thread on CO2 tank safety.
I hope any & all service establishments who change CO2 tanks frequently will
eventually move to bulk CO2 storage, which uses a lower pressure stationary
CO2 tank that is filled from a bulk truck right at the service environment.
This completely eliminates the need to move tanks, which aside from the rare
explosive incident, saves tank handlers from injury. Watching big CO2
bottles get moved around, especially up and down stairs, has always been an
uncomfortable thing, and I am sure there are a lot of injuries attributable
to CO2 bottle handling every year.
Keith Lemcke
Draught Beer Guild
------------------------------
Date: Wed, 20 Aug 2003 13:23:23 -0500
From: "Rob Dewhirst" <rob@hairydogbrewery.com>
Subject: Re: Sanitizers and Septic
>Does anyone have information on using
> sanitizers and it's effect on the septic system? I'm hoping that the
> relatively small amounts I use for five gallon batches once a month or so
> shouldn't be too detrimental.
I do not have some sort of authoritative study where people threw iodophor
in their septic system and studied the results, but it's pretty easy to see
the scope without even crunching the real numbers.
If you are mixing iodophor to taste-free sanitizing levels, and then pouring
that dilution into a septic tank of several hundred gallons, you are again
diluting this so low that the few organisms you might kills off will
regenerate within minutes, if not seconds.
Same applies for bleach.
Just use common sense and don't go overboard.
------------------------------
Date: Wed, 20 Aug 2003 14:50:30 -0400
From: "Martin Brungard" <Martin.Brungard@trow.com>
Subject: Starter Strategies
The responses to the question of how to best grow yeast starters were
encouraging. The guidance was welcome and it has created more thought on my
part.
It seems fairly clear that constant wort feeding is preferable to incremental
feeding in order to avoid the Crabtree Effect. It took a little digging to
figure what the Crabtree Effect was, but it seems that it's the phenomena of
the yeast producing alcohol, regardless of wort oxygen content, when the
glucose level exceeds 0.4 percent. Steve Alexander indicated that using a 7P
or lower malt wort will keep the starter below 0.4 percent. I'm pretty sure
that White Labs said they use a 5P malt wort for their production.
Steve suggested that if you set up a starter with constant wort feeding, you
would need to avoid overfeeding and underfeeding the starter, matching the
dosage with the yeast growth. Steve suggests that you would have to monitor
the CO2 and ethanol production to gauge the dosage rate. I did a little
research and found a reference in Vol 62, #2, of the ASBC Journal that
suggests that yeast do OK in an aerobic condition even when nutrients are
limited. So it seems that the only thing we really need to watch is
overfeeding. This may substantially reduce the sensitivity of the dosage
rate. I'm sure some smart person can probably calculate a dosage rate with
respect to initial cell concentration and wort strength. It's not me!
Jeremy Bergsman brought up another interesting idea for wort starters,
oxygenating the wort by storing it in an oxygen-filled pressure vessel. He
suggested creating a PVC or other type of container, but the obvious
container is a corny keg. As I understand it, this is similar to a Zahm and
Nagel tank that George Fix used to mention. Jeremy hypothesized that the
added wort would be thoroughly oxygenated as its added to the starter, but I
don't think that the minor volume of oxygenated wort dosed into the starter
would be sufficient to keep the starter aerated. So, continuous aeration
would still be needed. But, his idea does have several merits. The
pressurized wort would make it easy to meter wort into the starter with a
needle valve. The use of a corny keg also means that you could just pour the
freshly boiled wort without cooling into the corny and seal, hopefully
offering less infection risk.
The most important merit I see is the toxic effect against infection that
superoxygenation could provide the stored and pressurized wort. Does anyone
know what oxygen concentration would be needed to create a condition lethal
to most spoilage organisms? I think A.J. DeLange and George Fix did studies
of oxygen concentration in wort, but those apparently were at atmospheric
pressure. We could use some information on equilibrium oxygen concentrations
under various pressures and wort gravities. Anyone up for that? Another
drawback may be the effect of long-term oxygenation on raw wort. Would it
degrade somehow?
Wow, think of what a time savings you could get if you could keg a batch of
starter wort and have it keep for several months without infection. Is it
possible? I have to say that there are some interesting and potentially
practical starter strategies forming here. What are your thoughts?
Martin Brungard
Tallahassee, FL
------------------------------
Date: Wed, 20 Aug 2003 10:54:39 -0500
From: Brian Lundeen <BLundeen@rrc.mb.ca>
Subject: RE: anti-foam
> Date: Tue, 19 Aug 2003 06:08:43 -0400
> From: "Kevin Kutskill" <beer-geek@comcast.net>
> Subject: Re: Room enough for 10 gallons?
>
>
> Like Jeff Renner mentioned, there is a product called Foam
> Control, sold by Hop Tech (no affiliation, yada, yada, yada).
> You use 1 tsp. for every 5 gallons, and works like a dream.
Hop Tech must love you if you are using it up at that rate. I found 1/4 tsp
of their product was lots, sometimes all it took was a few drops. It depends
largely on the wort and yeast. I've switched to FermCap now. Picked up a
lifetime supply from a defunct brew pub for a pittance.
That does remind me of a question. Being a commercial brewery product, one
can assume FermCap is used largely in enclosed, vented kettles. Are there
any safety issues with having this stuff boiling in a homebrew kettle that
is filling up the air in your house or garage with the steam? I've noticed I
get a bit of a headache during the boils now, and wonder if it's from some
volatiles coming off from this stuff?
Cheers
Brian, brewing in Winnipeg
------------------------------
Date: Wed, 20 Aug 2003 16:45:46 -0400
From: Robert Sandefer <melamor@vzavenue.net>
Subject: Re: Munton's Wheat DME
David,
My supplier has told me that Munton's wheat dme is a 60:40 wheat:barley
blend, if my memory serves.
Hope this helps.
Robert Sandefer
Arlington, VA
------------------------------
Date: Wed, 20 Aug 2003 21:08:03 -0500
From: "Rob Moline" <jethrogump@mchsi.com>
Subject: Dr. Cone Responds-Conical Fermenters & Harvesting Yeast- Bob Fawbush
Dr. Cone Responds-Conical Fermenters & Harvesting Yeast- Bob Fawbush
Hi Dr. Cone,
Recently many homebrewers have purchased or
fabricated conical fermenters that employ
60 deg sloped sides & a bottom dump port.
My questions are as follows:
1)Assuming normal yeast fermentation
temperatures are employed - How many
days of fermentation should occur before
a brewer dumps yeast for reuse ?
2)Will the pressure that builds up on
the condensed yeast cake at the bottom
of the conical fermenter over the fermentation
cycle damage or harm future harvested yeast?
If so how ?
Thank you for taking the time to answer my
questions.
Cheers!
Bob Fawbush
Bob Fawbush,
The conical bottom fermenters are neat.
(1)Attenuation time depends on yeast strain, yeast health, wort gravity,
mashing protocol and fermentation temperature. The yeast should not be
settling appreciably until the end of the fermentation when all the sugar
has been used up (attenuation). Then it begins to flocculate and settle out.
The rate of settling is strain dependent, final gravity and how long and
well you have stored the re-pitched yeast.
You should note the fermentation activity, CO2 bubbling. When the CO2
bubbling dramatically slows down and you are near or at final gravity the
yeast begins to settle; three to five days depending on the temperature of
fermentation; three days at 80F, five plus days at 60F. These are very broad
suggestions. Be guided by the turbidity of the wort. If you can refrigerate
the mash, the yeast will settle faster and you can begin to remove the
settled yeast. Refrigeration places less stress on the yeast to be used for
the next pitching. Some beer makers will remove and discard the bottom 1/3
of the settled to get rid of most of the trub to minimize the carry over in
the next re-pitching. The remainder should be removed ASAP and refrigerated
at <4C. if possible.
I wish there was a more definitive answer.
(2) CO2 should present no problem in the fermenter size that the average
home brewer would use:
CO2 @ 0.2 atmospheres pressure stimulates yeast growth.
CO2 @ 0.5 atmospheres pressure begins to exert a negative effect on
yeast growth.
CO2 @ 3.0 atmospheres pressure stops growth
CO2 @ 3.0 atmospheres pressure does not stop fermentation-alcohol
production.
10 ft. height fermenter = 0.3 atmospheres.
Clayton Cone
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------------------------------
Date: Wed, 20 Aug 2003 21:08:05 -0500
From: "Rob Moline" <jethrogump@mchsi.com>
Subject: Dr. Cone Responds-Metabolism (follow up)-Fredrik
Dr. Cone Responds-Metabolism (follow up)-Fredrik
Dear Dr.Cone and Tobias!
Thank you very very much for answering all the questions!! :) :) Your
answers gave me some very valuable ideas how I need to revise and extend my
thinking on these topics!
I sure hope I am not beeing rude by asking too many questions considering
the limited bandwidth!? But If there is still space left at the end of this
two week period , I do have a couple of follow up questions.
(Lage phase and glycogen)
1) If there is basically no matebolic activity during the lag phase - is the
glycogen level not an issue during the lag phase? I had the impression that
low glycogen levels (like in stored yeast?) would cause an extended lag due
to some "free energy limitation"? I thought that until yeast start to uptake
and metabolise sugars, glycogen (and some others) was the energy supply for
whatever activites that is going on at this time? It this wrong? Are all the
adaptations in the lag phase of passive nature, like equalizing gradients?
requiring no metabolic energy to be spent? I understand that choice of
strain may impact the lag time, but for any given strain, what would be the
most important factors and variables be that determines the length of the
lag?
(sugar utilization)
2) From your answer about sugar utilization, to make sure I got it right,
did I understand things correct if I think there is no regulation of sucrose
uptake and invertase activity due to external glucose? so they would both
start at the same time and go on in parallell? If, as like I would guess(?)
that glucose uptake is alot quicker than sucrose uptake, would it be
possible to observe a small dip in CO2 production activity at the point
where the external glucose is consumed or reached soem treshold? I did
observer such a dip in a test I did. It sure is possible that ambient
conditions cause this, but in this case for some reason I think not, and the
dip coincidently occured at about 6% depletion of fermentables. I would like
to ask you about your opinon if you think that detecting such a dip (about
1.5 hours long and the "dip" was lowering the CO2 rate by some 15%) is
possible? Or do you think I should rule this explanation out and start
looking for another explanation of the dip?
/Fredrik
Fredrik,
Thanks for probing a little further into my reply to your question.
(1) You are correct in your impressions. Perhaps I overstated the lack of
metabolic activity during the lag phase. While it is acclimating itself to
its new environment, it is still very much alive and requires energy. This
energy does come from the glycogen and trehalose reserve present in the
yeast from the last fermentation cycle and left over from the refrigerated
storage period. If this carbohydrate reserve has been consumed during poor
and or extended storage, there will be an extended lag phase.
(2) Perhaps I should explain the sucrose step a little better. Sucrose
itself does not pass through the cell wall. Invertase is an external enzyme
that is present at the beginning of the fermentation. It begins immediately
to convert sucrose to glucose which joins with the initial glucose and
inters through the cell wall together via glucose permease. There is no
separate stage in which the initial glucose is used up, then the invertase
begins to convert the sucrose to glucose.
Glucose is a maltose inhibitor. Neither the permeases or the maltase
are
produced in the presence of >0.4% glucose. There is probably a short period
before these enzymes get into full production. Also, the maltose inters the
cell at a slower rate than glucose, so you would probably note a noticeable
slowing down or dip in CO2 production for a short period of time. Yeast
strain, wort composition, and fermentation temperature can effect this
transition period. You were very observant.
Keep in touch with future observations.
Clayton Cone
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------------------------------
Date: Wed, 20 Aug 2003 21:08:04 -0500
From: "Rob Moline" <jethrogump@mchsi.com>
Subject: Dr. Cone Responds - Aerobic yeast starters- Fred L Johnson
Dr. Cone Responds - Aerobic yeast starters- Fred L Johnson
Dr. Cone,
Some of us (or perhaps only I) are attempting to culture our yeast
starters in a respiratory state (with high oxygen and low glucose
concentrations). In my experience, I cannot deliver very much air to
the spinner culture using an aeration stone without creating too much
foam. I have made several beers with poor head retention when I've
included FermCap in the starter in sufficient quantity to prevent
foaming in the aerated starter, so I've tried another method that does
not require FermCap. I have been pumping filtered air at 2
liters/minute into the head space of a spinner culture with vigorous
stirring.
Questions:
1. Can pumping air into the head space with vigorous stirring provide
sufficient oxygen to the yeast to maintain them in a respiratory state
during incremental infusion feeding?
2. Can FermCap be used in aerated starters without detrimental effects
on the beer?
Fred L Johnson
Fred,
If your starter culture tank is 10 feet tall the answer is probably not.
If
it is several inches tall and a wide surface area, the answer is yes. A
sterilized cotton plug should allow enough air transfer to the surface of a
stirring wort culture to provide enough O2 for the yeast. Pumping a small
stream of filtered air into the head space would help.
I am not familiar with the composition of FermCap. Some antifoam
compounds
interfere with the oxygen transfer from the air into the wort media.
Stirring via a magnet stirrer should minimize or eliminate any foaming
problems.
Clayton Cone
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------------------------------
Date: Wed, 20 Aug 2003 21:08:04 -0500
From: "Rob Moline" <jethrogump@mchsi.com>
Subject: Dr. Cone Responds - Attenuation- Dave
Dr. Cone Responds - Attenuation- Dave
Dr. Cone,
I have a situation where I switched from bottled spring water to tap
water
filtered through the 10" carbon filter, found at http://www.morebeer.com/
(FIL32), and my beer's attenuation has suffered, seemingly, because of the
change. My attenuation levels for identical recipes went from 1.013 -
1.015 to 1.018-1.019.
Increasing the amount of aeration and/or oxygenation at the start has no
effect on the FG. Is there maybe a third cause I am overlooking, or can
filtering water through a carbon filter change the water chemistry enough
to alter the amount yeast attenuates the wort.
Thanks for any information you can provide,
Dave
Dave,
Water composition has a great effect on the mashing characteristics of
wort
and the fermentation characteristics of the yeast. Calcium and magnesium are
the two key minerals. The water should contain 50-100 mg. of Ca+++/liter
and 10-15mg. Mg+++/liter. Your tap water may be softer than the spring
water. I would try adding 1/6 tsp. of gypsum and about half that amount of
Epsom salts per gallon of water to be used for mashing.
The calcium is needed to protect the starch conversion enzymes in the
malted
barley. Magnesium is needed in the yeast metabolic process.
Let me know if it works.
Clayton Cone
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------------------------------
Date: Wed, 20 Aug 2003 23:10:09 -0400
From: "Tanksalot" <tanksalot@rogers.com>
Subject: CO2 Tanks
CO2 tanks can be dangerous. The gas is compressed (to a liquid) under
pressure approaching 1000 psi. But there is (or should be) a working Safety
at the Tank Valve. This allows the gas to escape safely, but very noisily
in the event of a problem at the valve end of the tank. If the Safety Valve
blows, all the gas escapes and the tank cannot be refilled until the problem
is corrected; most gas suppliers will simply replace the whole valve
assembly as it is not practical to rebuild the Safety or "pressure relief".
I live in Ontario, Canada and tanks are stamped so they must be
hydrostatical tested every five years before they can be refilled.
Two years ago I had some 2.5# and 15# tanks refilled, and foolishly left
them in the trunk of my car for a few very-hot hours. It sounded like
Vietnam as the Safety Valves in turn vented all of the gas and coated the
trunk lid with "dry ice" ..even the last two tanks which I tried to cool
with water. In this case it was an error by the welders' supply shop where
they were overfilled. Larger tanks of course would be more of a hazard, but
I don't believe there would be a "rocket" flying around your brewery. CO2
is the gas used in many fire extinguishers so it's not poisonous or
flammable. Anyway, it is best to treat any compressed gas with respect!
Larry at Tanksalot
------------------------------
Date: Wed, 20 Aug 2003 23:36:43 -0400
From: "-S" <-s@adelphia.net>
Subject: Re: The reason for the seemingly excessive oxygen requirements?
Had to abbreviate for the 8kb limit but ...
Curious Fredrik writes ...
>Biomass(dry) is about 1% sterols (according to George Fix)
>For simplicity I assume sterols = 100% ergosterol
>squalene contains 0% oxygen
>ergosterol contains 4% oxygen
>
>[...] O2 requirements for new healthy biomass
>is 0.04%
>
>Assuming 100% utilization this indicated that a biomass yield of 10% on a
10
>plato wort would take no more than an initial oxygen level of about 3-4
ppm.
Biomass growth is 5% according to Balling ...
[ 200g maltose + 1 g ammonia -> 10g yeast + 97.5g EtOH + 93.6g CO2 ]
Your 10P wort would grow enough yeast to require 2ppm of O2. *BUT*
in normal brewing (not starters) you pitch about 10%-25% of this
amount of yeast so it's a fraction of 1ppm for sterols. O2 utilization
efficiency is obviously between 50% and 100% for each oxygen in
sterol.
>1) maybe there are other processes competing for the oxygen? If so which
>onces? I've assumed that nonenzymatic reactions are not relevant in the
>timeframe considered here, like in a starter, what do you think?
More oxygen is required for the formation of unsaturated fatty acids(UFAs)
than sterols. UFAs are extremely importantly wrt cell membrane properties.
Several sources suggest that for air saturated wort (around 7-8ppm of O2)
pitched with lipid depleted yeast that 10% of the O2 is used for sterol
synthesis and 15% for UFA synthesis. I can't say exactly where the other
75% of oxygen is used, but the 'haem' protein is involved in the initial
oxygen
uptake for most yeast oxygen pathways. Respiration is one obvious
use for O2.
Also fresh wort is full of reducing substances capable and ready to oxidize
at the drop of a hat. Fresh wort will chemically compound O2 saturation
levels (~15ppm for pure O2) in a matter of several hours. Some of the O2 is
lost to wort staling in a nonenzymatic way. In the mash the enzymes can
use up saturation O2 levels in minutes if not seconds. In the fermenter
the non-enzymatic staling processes require hours for the asme activity.
>2) The rate of oxygen uptake is the limiting factor rather than the
>absolute depletion of oxygen. Due to the diffusion kinetics [...]
Oxygen induction is an active process regulated by several genes, not
passive diffusion. Pitching levels of yeast can remove saturation levels
of O2 in a matter of 20 minutes under the right conditions so uptake
rate isn't the issue.
>3) there is a waste of oxygen in the synthesis of ergosterol?
Very likely, but I can't say how much.
Yeast, like other cells, have very strong mechanisms for handling any free
oxygen radicals that might result as 'waste'.
>What is the proper way to resolve this confusion?
I'd start with a good book. Dr.C.Cone mentioned a few. One I like a lot
is "Brewing Yeast and Fermentation" by Boulton and Quain, 2001,
ISBN 0-632-05475-1
>If the wort gets really really depleted of oxygen (=0 ppm), whayt the heck
>is the oxygen used for? :). It seems from my crude estimations that it
can't
>all go into sterol synthesis? Are my estimates flawed?
No - your estimate for sterol is a very good first step, but you neglected
the other oxygen ereq - UFA and then again no one seems to know
exactly where all the O2 goes besides respiration.
>What did I miss? help!
I think you didn't express your motive. It's interesting to note that yeast
seem to consume some 3 or 4 times their minimum requirement of O2 and much
of the excess beyond requirements goes to unknown destinations - but SO WHAT
! Yeast metabolism includes at least several hundred thousand reactions
which are certainly not all understood quanitatievlyt in relation to each
other.
Why not start your search for understanding by considering which factors
cause
significant changes in brewing behaviour (flavor, fermentation, performance,
flocculation and health) rather than try to hunt down the destination of
every bit of every nutrient. The first task is merely very difficult, the
second is almost impossible. The quant info simply does not exist.
Great questions Fredrick - but it's time to use that library card and do
some hunting through the technical literature. If I can help you with
specific references or details, please let me know.
-Steve Alexander
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End of HOMEBREW Digest #4328, 08/21/03
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