FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
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Contents:
yeast propgation (Rob Schlank)
Re: Should I repitch? (Stephen Jorgensen)
Should I repitch? (Scott Birdwell)
Helium ("Chad Stevens")
more yeast perf ... pt 1 ("Steve.Alexander")
more yeast perf ... pt 2 ("Steve.Alexander")
Kalamazoo Stout (Tim Eitniear)
2009 South Shore Brewoff - competition announcement ("jeff_ri")
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Date: Tue, 17 Feb 2009 09:11:56 -0500
From: Rob Schlank <rschlank at comcast.net>
Subject: yeast propgation
Joshua WIlkins wrote, "The smack packs that Wyeast uses
contains nutrients and the sachet that you pop on the inside is the yeast
cells."
Not to nitpick, but this is incorrect. The sachet contains the nutrients,
not the cells. You can, if you wish, pitch the cells into a starter without
'smacking' the sachet. This is per Dave Logsdon at Wyeast in an interview, I
believe from an old TBN show. I have done this myslef several times, though
now I smack the pack just to get the nutrients into the starter as well.
- --
Rob Schlank
------------------------------
Date: Tue, 17 Feb 2009 09:35:17 -0600
From: Stephen Jorgensen <stephen at ultraemail.net>
Subject: Re: Should I repitch?
"I have an IPA in the secondary for about 10 weeks. It looks clear and tastes
decent upon sampling."
In my experience there is no more disappointing result in home brewing
than a bottle of sweet, flat beer. Yes you should use fresh yeast to
package your IPA but an entire envelope is not necessary.
I don't have the correct cells / ml numbers to hand but I am sure there
are multitudes of brewers reading HBD that know them by heart. I
generally use about 1/10 the amount for bottling as I did when pitching
the wort. In the case of Danstar Nottingham (no affiliation) which is
my bottling yeast of choice I use 2-3 g for a 6 gallon batch. For an
IPA I would go with 3.
------------------------------
Date: Tue, 17 Feb 2009 13:37:03 -0600
From: Scott Birdwell <defalcos at sbcglobal.net>
Subject: Should I repitch?
Regarding Tom Puskar's question, "Should I repitch. . ."
"For a number of reasons ranging from illness, work and family issues,
I have
an IPA in the secondary for about 10 weeks. It looks clear and tastes
decent upon sampling.
I'm hoping to bottle it (FINALLY) this coming week and wondered if I
should
add some additional yeast for carbonation. I keep a few envelopes of
dry
yeast around and could proof one up and add it to the bottling
bucket. I
haven't checked the gravity in a few weeks but last check it was around
1.015 and hadn't changed for a while."
Tom,
It's like chicken soup. . . it couldn't hurt! Just rehydrate the
dried yeast in some lukewarm water and mix it thoroughly into the beer
just before/after you mix in your priming sugar. You should have
carbonated beer within a couple of weeks. Good luck!
Scott Birdwell
DeFalco's Home Wine & Beer Supplies
Houston TX
------------------------------
Date: Tue, 17 Feb 2009 14:35:49 -0800
From: "Chad Stevens" <zuvaruvi at cox.net>
Subject: Helium
Got my CO2 tank filled yesterday. On the way out of the shop I saw a helium
tank. Brewers being mad scientists by default, I thought to myself,
"wouldn't that be an interesting party trick, Helium 'carbonated' beer."
Take a sip, then sing, "We represent, the lollipop guild...."
Anyone tried it?
Chad Stevens
QUAFF
San Diego
www.sdfair.com/beer
------------------------------
Date: Tue, 17 Feb 2009 18:03:56 -0500
From: "Steve.Alexander" <steve-alexander at roadrunner.com>
Subject: more yeast perf ... pt 1
Uhoh - 8k bouncy bouncy
I've used imprecise language and now several ppl have posted their own
(sometimes odd) views on terminology and we are making a mish-mash of
this discussion. In common use "ferment" merely means microbiological
activity. I didn't really think we need/want to delve so deeply on this
one but ....
According to Brock's "Biology of Microorganisms", a very widely used and
highly regarded text we have ... "Fermentation - Catabolic reactions
producing ATP in which organic compounds serve as both primary electron
donors and ultimate electron acceptors and ATP is produced by
substrate-level phosphorylation". And, "Respiration - Catabolic
reactions producing ATP, in which either organic or inorganic compounds
are primary electron donors and organic or inorganic compounds are
ultimate electron acceptors". If you study the definitions carefully
you will see that respiration is any ATP energy pathway, while
fermentation additionally requires organic donors, organic acceptors and
substrate-level phosphorylation (as opposed to oxidative phosphorylation
pathway). Brock divides catabolic pathways into "aerobic respiration"
and "anaerobic respiration", and OBVIOUSLY he's not referring to the
environment but the metabolism.
According to Brock's ... Fermentation IS a type of respiration !!!!
Aerobic/Anaerobic can and usually does refer to the metabolism NOT the
environment.
. so perhaps we all get a big fat F- for terminology.
Nester-Robert-Nester "Microbiology", and Stryker "Biochemistry" says
that respiration requires any inorganic electron acceptor.
Mathews-vanHolde*, *"Biochemistry", says respiration requires oxygen as
the electron acceptor.
===========
The two concepts we are trying to distinguish here are related to how
the metabolic phosphorylation of ADP to ATP occurs, but thats awfully
deep into the nuts & bolts.
In conventional brewery fermentation with Saccharomyces yeast (of
course) none of the catabolic(energy producing) pathways use free
oxygen. Brewery yeast induce sugar or create these from enzymatic
breakdown of sugar polymers.
First, each hexose sugar is converted to two pyruvates + 2 H2O + energy
as a net +2 ATP. This is known as the Embden-Meyerhof-Parnas (EMP)
pathway and is one of several glycolytic pathways. The ATP is produced
by substrate-level conversions of bisphosphoglycerate and
phosphoenolpyruvate.
The pyruvate can readily, enzymatically be converted to lactate (as in
your muscles) acetate+formate or acetaldehyde+CO2. In yeast the
pyruvate is converted to acetaldehyde+CO2 and the acetaldehyde is
reduced (the organic electron acceptor) into ethanol.
The EMP pathway also converts 2 NAD+ to 2 NADH and this is a great
energy store (1 NADH can be converted to 3 ATP with some oxygen) BUT to
accomplish the redox balance all of the NADH must be used to reduce
acetaldehyde to ethanol. In anaerobic condition it is always necessary
to use the NADH of glycolysis to reduce the pyruvate product.
No oxygen is required for this catabolic pathway, and the net energy
yield is only 2 ATP per hexose.
- --
Under ABNORMAL conditions we can get brewing yeast to use another
catabolic pathway using sugars. The yeast induce sugars as before. The
EMP glycolytic pathway occurs too producing pyruvate and ATP as before.
The next pathway is the "Citric Acid Cycle"(CAC) , aka Tri-Carboxylic
Acid Cycle(TCA) and more formally as the Szent-Gyorgyi/Krebs cycle (note
Szent-Gyorgyi is one guy). The major plot is that the 3-carbon chain
pyruvate is converted to 3 CO2 molecules by repeated decarboxylation.
First the pyruvate is converted to AcetylCoA+CO2, then the Acetyl-CoA
plus an oxalacetate(from...see below) becomes ketoglutate+CO2, then
the ketoglutarate becomes succinyl-CoA+CO2 and finally the succinyl is
reverted to oxalacetate and added back at the start of the next cycle.
The CAC+Glycolysis results in net yield 38ATP of energy per hexose and
only 4 of the ATPs of the total produced are by substrate-level
phosphorylation, the rest by oxidative phosphorylation.
========
Heading out of the chem lab and back toward the brewery .....
There are some silly notions perpetrated and/or perpetuation by poorly
researched HB books. Brewery yeast under normal brewing conditions
NEVER use the CAC cycle (almost never). Not even when they are pitched
into well oxygenated normal wort. Now IF you use an open fermenter then
after all the sugars are used up the yeast can oxidize ethanol back into
aldehyde then convert to acetyl-CoA which can then enter the CAC cycle
and yields a lots of energy. The "back up the tree" process can also
throw off some lactate and acetate. It's unclear how rapidly this path
can operate but distilleries use open fermentation and I've seen figures
indicating that a few percent of the ethanol is used per 24 hours of
extra delay. I would imagine that oxygen is a limiting factor in those
conditions.
If you can grow yeast with their metabolism using the CAC cycle, then
there are some metabolic and environmental differences. The yeast are
constantly exposed to free oxygen (needed for the oxidative
phosphorylation) and so they don't accumulate squalene (a precursor to
sterol) but instead they contain a high level of sterol. Similarly
with ever present oxygen yeast can construct (mostly mono-) unsaturated
fats and so these yeast have the best cell membranes around. As the
yeast hit a growth limitation then I would expect that they will store
"storage carbohydrates" abnormally; glycogen accumulates in response to
growth limitations, but also degrades in the presence of oxygen.
Trehalose accumulates in response to a wide array of stresses including
nutrient deficit. So pitching yeast that have finished in aerobic
metabolism is probably nearly ideal except for glycogen, and that's
probably not terribly important unless you plan to store the yeast (then
an anaerobic final finish w/ a little sugar added might be best); and
since these are high in UFA&Sterol so there is less need to aerate the wort.
Yeast in anaerobic conditions suppress the enzymes of the CAC cycles,
and in aerobic conditions they suppress the creation of cytochomes that
are involved in the electron transport for redox balance (far less is
needed). This is NOT a big deal unless you are the sort who gets
ants-in-the-pants if a fermenter isn't bubbling in 20 minutes.
- --
(continued)
------------------------------
Date: Tue, 17 Feb 2009 18:04:25 -0500
From: "Steve.Alexander" <steve-alexander at roadrunner.com>
Subject: more yeast perf ... pt 2
(continued)
Kai T suggests ....
>> > > It might be that low gravity propagation isn't
>> > > good either b/c the yeast may get uses to the lower alcohol/sugar
>> > > concentration both of which are stress factors.
>>
No. High gravity is just a ion pump stressor (yeast must expend more
energy moving ions across cell membranes) and there is no way to
accumulate a tolerance to the added workload except to include more
sterol & UFA per cell to reduce "leakage". It's always best to
propagate yeast at 5-7P.
Joshua Wilkins mentions his experience with a commercial propagator but
.. this doesn't exactly hit the mark either. This sort of propagation
is aimed at providing oxygen to yeast culture, such as a scintered stone
would, but it is not aimed or creating conditions for aerobic metabolism
(the CAC cycle). There is nothing very expensive about scaling this
down to HB level.
His other comments fall solidly into the "old brewers tales" category.
That yeast develop resistance to ethanol and hops doesn't match anything
I've ever read anywhere - and the fact is that all fermentation produces
intracellular ethanol. The "resistance" or more correctly high
tolerance of high level is of extracellular ethanol is from several
studies only related to cell membrane quality and the absence of the
environmental stressors like excess CO2 in solution and the presence of
several specific amino acids which reduce the osmotic stress effect.
When repitching into a barleywine you can and should use sterol&UFA rich
yeast propagated at ~5P.
The idea that you should walk yeast through the sugars they consume (the
order glucose,fructose, maltose, maltotriose is common) before you plop
them into fresh wort has absolutely no advantage. The presence of
glucose inhibits the transport of the maltose & maltotriose ; maltose
inhibits the maltotriose and so on ... and the enzymes for transport
and hydrolysis simple don't last long enough to make any difference at
all. There may be a slight advantage in propagating yeast on glucose
since it's the first sugar they'll get at pitching, , but frankly it's
pretty far down the "don't care" list. So long as the yeast is
reproducing correctly and has the necessary nutrients, then they carry
all the genetic machinery to produce (and alternatively inhibit) the
right enzymes for their *current* conditions and it only takes minutes
for them to make a transition if healthy.
*IF* (this is a huge if) you could force yeast into using the CAC cycle
they would produce roughly 10X the biomass per unit sugar so wort would
be too deficient in nutrients to be useful. Adding nitrogen can
alleviate the nitrogen deficit *BUT* I've recently read that (low)
nitrogen plays a huge role in keeping yeast in aerobic-respiration
metabolism. If nitrogen is low then respiration is preferred (low
nitrogen limits sugar transport), but the low nitrogen also inhibits
growth rate. So you really need to carefully feed both sugar and
nitrogen. Boulton & Quain "Brewing Yeast and Fermentation", suggest
that the only way to get yeast to respire is to slowly feed sugar in a
very low nitrogen environment or to use a chemostats under carbon
(sugar) limitation. A chemostat is a bit of lab gear that allows one to
adjust the input rates into fermenter (with corresponding output) so
that the vessel contains a stable culture. It's not useful for biomass
creation. There are about 3 dozen well know required yeast nutrients
aside from nitrogen and a carbon source(sugar ...) and these won't come
cheap. Urea and a good yeast nutrient are a start but what exactly
provides biotin and pantothenic acid and enzyme cofactors and in what
proportion ?
The only other CAC approach that makes sense is to use a substrate than
cannot undergo glycolysis - so feed your yeast pyruvate or lactate or
ethanol, xylitol or certain glycosides and let then run it thru the CAC
cycle. These are some so called "oxidative substrates", but the trouble
is that aside from pyruvate, which yeast can use which substrate is hit
or miss (The UK NCYC has very incomplete tables for their yeasts).
Then we have the question of how fast can yeast really use oxidative
substrates. This may make this approach even more impractical; I
believe that most can use ethanol, but the rate may be too slow to
provide a decent propagation method.
Trying to grow yeast with CAC metabolism is an interesting hack, but
ultimately costly and difficult. I might feel differently if sugar was
vastly expensive or else if pyruvate and other nutrients very cheap; but
just the opposite is true. It may have a place in producing yeast for
freeze-dried storage, but that's a special application I don't need to
practice. If you learn to do this cheaply and effectively please drop a
note, b/c it would be a great propagation technique.
The only really practical approach I see here is that if you bump oxygen
into a conventional wort starter (say on a stir plate or with a stone)
then your yeast will still be well supplied with UFA and sterols and
you'll have the happy co-incidence that wort has about the right mix of
sugar and nutrients to grow yeast using glycolysis only.
As a very relevant aside, Boulton pioneered the "yeast oxygenator"
method used commercially as Bass Brewers Limited. They take a yeast
slurry, presumably from a finished batch, and add just a bit of 3P wort,
then the add continuous oxygen over a period of several hours. They
continuously measure the yeast oxygen uptake rate. In about 3 hours
the oxygen uptake rate peaks then it drops to a low figure after another
3-4 hours. At that point the yeast have degraded their glycogen store
and produced all the sterol possible. This is pitched directly into
UNoxygenated wort in fermenter. They give figures showing the beer
attenuation rate is superior and far more consistent than wort
oxygenation. Also the there is no significant difference in esters or
other flavor active yeast by-products.
Yeah - by all means get a lot of oxygen into the starter, and less into
the wort ! But there isn't any practical gain to pushing the metabolism
to oxidative phosphorylation on the HB scale.
-S
------------------------------
Date: Tue, 17 Feb 2009 20:17:10 -0600
From: Tim Eitniear <timeitniear at sbcglobal.net>
Subject: Kalamazoo Stout
Hi,
Trying to clone this lovely beer. Found something in the archives from
2002 and I have the zymurgy articles from 2003. Any one have any
suggestions or have found a AG solution to this beer?
Tim
- --
http://nottawaseppibrewing.wordpress.com
A guy walks into a pub with a lump of asphalt on His shoulder, He says to
the bar man give me a pint and one for the road.
------------------------------
Date: Tue, 17 Feb 2009 22:10:38 -0500
From: "jeff_ri" <jeff_ri at cox.net>
Subject: 2009 South Shore Brewoff - competition announcement
The 2009 South Shore Brewoff is the 14th annual homebrew competition
organized by the South Shore Brew Club. The competition is organized to
provide entrants with a high level of evaluation and valuable feedback on
their brewing efforts. Whether you are a novice or a seasoned brewer, we
welcome your participation.
The competition will be held in Mansfield, MA on April 18th, 2009. The
entry deadline is April 3rd, 2009.
All entry information is on the club webpage at:
http://www.southshorebrewclub.org/
Geoffrey McNally (judge coordinator)
Kevin Farrell (competition organizer)
------------------------------
End of HOMEBREW Digest #5506, 02/17/09
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