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HOMEBREW Digest #5299
HOMEBREW Digest #5299 Sun 24 February 2008
FORUM ON BEER, HOMEBREWING, AND RELATED ISSUES
Digest Janitor: pbabcock at hbd.org
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Contents:
Re: oxygen and fatty acids and sterols for dummies ("steve.alexander")
Providing sterols to yeast (Fred L Johnson)
Back Issues ("Val J. Lipscomb")
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Date: Sat, 23 Feb 2008 08:35:22 -0500
From: "steve.alexander" <-s at roadrunner.com>
Subject: Re: oxygen and fatty acids and sterols for dummies
Matt Wallace writes,
> I'm interested in ways to give yeast everything they need to brew
> very high
> gravity beers.
Yeast require oxygen to produce UnsaturatedFattyAcids(UFAs) and sterols
- two different categories of lipids. It's been demonstrated that yeast
can live anaerobically if supplied with these.
Yeast incorporate UFAs into cell membranes which has a huge impact on
flexibility and permeability of the membrane, critical to high gravity
brewing. Yeast can directly incorporate fatty acids (either free or the
n-acyl glycerides in veggie oil) directly into cell membranes. Your 1/2
drop of olive oil is too little. If you search the archive you'll find
my calculation, but it's on the order of ~1tablespoon of oil, ~14grams,
for 5gal of 12P wort and more for high gravity. Adding a little
lecethin can make the oils more accessible to the yeast.
Yeast will incorporate plant sterols into membranes, but there aren't
any readily available concentrated sources in your kitchen. You may
find plant sterol pills in health food stores. Vitamin D is a sterol
too, but not very concentrated. Sterol is a critical part of cell
membranes and it affects membrane fluidity, but unlike UFAs seems to
have less of a role in permeability except to the extent they limit the
quantity of membrane tissue.
> -Sterols are generally the major limiting factor in yeast growth, and
> oil
> doesn't provide them in any significant amount.
Right. When the sterol level drops too low the yeast cease to reproduce
since they can't create more membrane. This *seems* OK since the
existing yeast cells are still alive and fermenting, but that's false.
When yeast metabolism recognize the lack of a growth factor (sterol,
amino acids, biotin and about 50 others) they change the cell surface to
flocculate, and they become dormant and the fermentation rate drops by a
factor of 10+ (stuck fermentation) !
> -There is evidence to suggest that providing yeast with "free fatty
> acids"
> can result in enhanced yeast growth and attenuation.
>
Yes, but ... . Yeast don't need UFAs to grow ! They can create
saturated-FAs(SFAs) anaerobically and use these. The problem is that
the membranes created with more SFAs are inferior. Consider that wort
has a relatively high initial molarity (concentration of molecules in
solution) and as yeast ferment each molecules of maltose into 4
molecules of ethanol the molarity increases. The problem is several
times worse in a high gravity brew. Osmotic pressure at the cell
membrane is created by this concentration of solute. The yeast have to
expend energy pumping metabolic by-products out of the cell across the
pressure gradient and the amount of energy increases with molarity. The
pressure causes more leakage into the cell so the cells must also expend
energy pumping "bilge" out too. The UFA poor membranes are leaky which
limits growth in a high molarity low oxygen environment.
> -a good way to give those free fatty acids to your yeast is to add a
> small
> amount of saponified flax or olive oil, i.e. soap.
>
The action of soap (salts of FAs) on bacteria is to disrupt cell
membranes by reducing surface tension, and I think it should do the same
to yeast membranes. It's also unclear how yeast could ever use the salt
of FAs to build membranes. Avoid soap. Instead consider flax oil mixed
well with a little lecethin (liquid form).
> But I am still curious if there are practical ways for the
> homebrewer to cheat ....
High gravity brewing is a special topic - and there are many ways to
improve the results.
Total UFAs and sterol includes that in the yeast you pitch, plus the
amount produced form the oxygen of aeration within hours after pitching,
plus a modest amount in the wort. This represents all the UFAs and
sterols in the final yeast cake. In ale brewing we expect a 10x
increase in the dry yeast mass, so the final yeast have only 1/10th
concentration of the UFAs and sterol as the cells early in the
fermentation. In high gravity brewing the yeast may not be survive with
only 1/10th of UFA & sterol and this immedialte implies a higher
pitching rate to for cell membrane quality as well as a higher pitching
rate to accomodate the extra extract. Your 28P beer is about 2.5 times
normal gravity, but you may need 4 or 5 times the normal pitching rate.
First - choose a yeast that can tolerates high gravity without special
treatment. Pitch enough yeast. A 5gm dry yeast pack or a wet XL pack
is IMO barely sufficient for 5gal of 12P ale. and you would start with
perhaps 3x that rate and plan on more later. You can reportedly aerate
the pitched wort up until the time the fermentation takes off - perhaps
12 or more hours after pitching. Dissolved CO2 increase molarity,
decreases pH and inhibits some of the yeast metabolic processes so
shaking, stirring or otherwise removing CO2 helps. Adding well aerated
yeast from a starter well into the fermentation is a good way to bump up
the sterol+UFA in the fermenter.
In one Canadian study they added yeast extract (as nutrient), 24ppm of
ergosterol and 0.24% vol/vol of tween80 (esters of UFAs). That's half a
gram of sterol per 5 gal and may be available in plant sterol pills.
The tween80 is similar to 48ml or ~3 tablespoons of veg oil per 5
gallons of beer. They produced 14% to 16% ABV beer using conventional
brewing yeast after 5 days of fermentation !
-S
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Date: Sat, 23 Feb 2008 08:46:28 -0500
From: Fred L Johnson <FLJohnson52 at nc.rr.com>
Subject: Providing sterols to yeast
Matt wonders about how to provide sterols to yeast.
I've also wondered about a way of providing sterols to yeast, but
I've never read exactly which sterols the yeast contain and haven't
bothered to look this one up. It really doesn't matter. If one were
to extract the sterols from the yeast in bulk and then provide the
whole extract to the yeast, it would probably be beneficial to the
yeast. Separating out the sterols from the other extractable lipids
would get pretty involved and probably isn't worth it.
The extract may need to be emulsified with soap to make them
available to the yeast. The extract itself may actually be
emulsifiable after drying and sonication in water or an appropriate
buffer. There are probably enough phospholipids in the extract to
make the emulsion, although I'm not sure how stabile it would be. In
any case, it would not be difficult to prepare a lipid extract and
then prepare a stabile emulsion.
Incidentally, the author of the olive oil report told me that he and
his colleagues do not believe that olive oil itself is useful to the
yeast. Rather, they believe the trace amount of free fatty acids
present in the olive oil are more likely the cause of the effects
observed. If I recall, this was never mentioned in the original report.
Fred L Johnson
Apex, North Carolina, USA
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Date: Sun, 24 Feb 2008 13:08:29 -0600
From: "Val J. Lipscomb" <vlipscomb at satx.rr.com>
Subject: Back Issues
Due to medical concerns my Doc has decreed that I no longer can consume
alcohol in any form. As a homebrewer for over 20 years I have accumulated a
lot of
magazines and books. I have, for sale, 3 complete years of Brewing
Techniques plus
5 single issues. I also have 12 complete years of Zymurgy plus 10 single
issues. I am
asking $5 per issue and $25 per complete year.I would prefer to sell them
all to one
buyer and would give a substantial discount for that and,being a really
good guy,
would donate 10% to the HBD which has given me much enjoyment and information
over all these years. E-mail me for a complete list of the magazines and
brewing books.
Val Lipscomb-formerly brewing in San Antonio
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End of HOMEBREW Digest #5299, 02/24/08
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