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	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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