yeast starters

[Zwickel]

Most ive done it is 4 times in a row without any problems -
........was the best by a long shot!

+1

 

[Bribie G]

In about half an hour I'm going to rack an ale into secondary, swish the yeast cake around till it's runny then pour about half of it into a clean sanitized fermenter. Then pour in a cube of an identical wort made yesterday then off it goes again (its a fairly exxie Wyeast 1768).

 

[A3k]

Yeah i'm about to do this. Using the WYeast oktoberfest, brewed a Munich Helles, then am going to dump an Oktoberfest on it.

 

[bowie in space]

In about half an hour I'm going to rack an ale into secondary, swish the yeast cake around till it's runny then pour about half of it into a clean sanitized fermenter. Then pour in a cube of an identical wort made yesterday then off it goes again (its a fairly exxie Wyeast 1768).

What are you going to do with the other half bribie?

 

[drsmurto]

I dont feel attacked, Im always happy to be stand errected, corrected.
My fave beers are without doubt, Belgian styles.
2nd to that, I enjoy the English beers, and I certainly have been under the impression, from stuff Ive read, and my own limited expreience, that lower pitching rates of any yeast leave me with more yeast armoas in the beer.
Wether these aromas are something that would slip me out of style in a comp, I can not say, but if I brew an Emglish Mild, style, say, then I prefer for the beer to have a lot of yeast character.
Do you get me?

Putting my kneck out here, im similair, I dont build up adequate starters with pale ales, and most of the time its been fine, in fact I actually quite like the esters you can sometimes get, for example I pitched a 1L starter of 1469 into 20 litres of 1052 and the esters and stone fruit im getting of it is devine :icon_drool2: Allthough I did it once with 1026 and :icon_vomit:

I think you missed my poorly made point.

Making a starter and pitching (arguably) a more appropriate amount of yeast doesnt (IMO and in my experience with english ale yeast) result in less yeast derived esters.

I would go further and argue (again, english ales as my example) that esters produced by happy yeast are more desirable than those produced by a stressed yeast.

I dont doubt that you are noticing more esters produced from stressing the yeast but what i want to open up a discussion on is - are those esters desirable compared to those derived from a happy yeast?

I'd like to know - any microbiologists out there like to enlighten me/us?

 

[white.grant]

I'm not so sure about reusing uncleaned fermenters and dropping nice fresh wort on entire yeast cakes. There is just way too much other stuff including dead cells, hop matter and other crusty bits coating the sides and trapped in the tap. You're also very likely to overpitch using a whole yeast cake.

I prefer to swirl the yeast cake with boiled and cooled water and then remove the required amount of yeast slurry to repitch onto wort in a clean and sanitised fermenter. Cleanliness counts I reckon.

cheers

grant

 

[Bribie G]

What are you going to do with the other half bribie?

put it in a sterilized Schott bottle in the fridge for my next UK bitter. :icon_drool2:

 

[Sammus]

I think you missed my poorly made point.

Making a starter and pitching (arguably) a more appropriate amount of yeast doesnt (IMO and in my experience with english ale yeast) result in less yeast derived esters.

I would go further and argue (again, english ales as my example) that esters produced by happy yeast are more desirable than those produced by a stressed yeast.

I dont doubt that you are noticing more esters produced from stressing the yeast but what i want to open up a discussion on is - are those esters desirable compared to those derived from a happy yeast?

I'd like to know - any microbiologists out there like to enlighten me/us?

I dont have a PhD in microbiology or anything, but the wyeast presentation on the bjcp site (see under continued education) they did a bunch of testing/tasting and for the wheat yeast example, the preferred sample was one pitched with 1/4 the number of yeast cells than the other style worts... What I'm trying to say is that I think there are times when the esters produced during the growth phase of the yeast are at least sometimes desireable...

 

[drsmurto]

I dont have a PhD in microbiology or anything, but the wyeast presentation on the bjcp site (see under continued education) they did a bunch of testing/tasting and for the wheat yeast example, the preferred sample was one pitched with 1/4 the number of yeast cells than the other style worts... What I'm trying to say is that I think there are times when the esters produced during the growth phase of the yeast are at least sometimes desireable...

Have heard that mentioned about wheat beers.

But lets be honest, what would a wheat beer be without yeast derived esters? Tasteless megaswill i suspect..... h34r: but then i dont make wheat beers so i shouldnt really comment

My points were related to my experiences with english ale yeasts

 

[Swinging Beef]

Have heard that mentioned about wheat beers.

But lets be honest, what would a wheat beer be without yeast derived esters? Tasteless megaswill i suspect..... h34r: but then i dont make wheat beers so i shouldnt really comment

My points were related to my experiences with english ale yeasts

Im happy to be involved in the guinea pig process in the interest of improving fine english styled home brews!
Ill try to sort myself out a split batch into two fermenters under varied yeast conditions to check it out.
Probably chould be clear to do one of these in early June.
Anyone wanna suggest me an amber ale recipe to do this with?
And as for wheat beer.. yes.. if it wasnt for decent carbonation, other spices and yeast, I reckon it would be a sad lonley brew.

 

[muckanic]

I dont doubt that you are noticing more esters produced from stressing the yeast but what i want to open up a discussion on is - are those esters desirable compared to those derived from a happy yeast?

Fix in his "Brewing Science" book makes a throw-away comment that cold break in the ferment can reduce the incidence of unpleasant acetate esters. I assume he's referring to ethyl acetate, and contrasting this with the fruitier, higher molecular weight esters. Extrapolating, the provision of unsaturated lipids is meant to substitute for oxygenation, and oxygenation and pitching rate are both crucial to avoiding yeast stress in high gravity brews.

Maybe the weizen brewers are getting away with underpitching because the gravity is not sufficient to show the damage? Weizenbocks could be a different matter. OTOH, Fix could simply be saying that cold break reduces all esters equally. The more recent olive oil research could be a clue.

 

[muckanic]

Some more thoughts after a bit more reading. Fix reiterates that respiration and esterification are competing processes, meaning that one happens at the expense of the other. This might seem a little odd in light of the common sentiment that "more growth means more esters". My interpretation is that this is not an either/or situation, and that there are basically three situations:

1. Underpitching, in conjunction with underoxygenating and/or lack of lipids. Result: weak growth, stressed yeast, and probably a stalled ferment. Made more acute by high gravity brewing, because the pitching rate and oxygenation requirements are that much higher. We know that this can result in solvent-city, but it is not clear that this also results in fruit-city to the same degree.

2. Under to adequate pitching, but in conjunction with appropriate oxygenation and lipids. The Fix view seems to be that this results in adequate yeast growth and consequently suppresses esterification. However, this also seems to be the situation that most weizen brewers refer to when they say they are "stressing" their yeast.

3. Pitching to such an extent that no yeast growth is required. Fix doesn't have an explicit view on this, but of course there is a common sentiment (originating from Wyeast?) that this makes for bland beer. Personally, I'm not so sure that the yeast characteristics can be suppressed that easily. Ales don't suddenly become lagers, for example.

Obviously, oxygenation and lipid technique are wild cards in any discussion of these issues. Most amateurs don't separate cold break fully, and some practise open fermentation (unless possessed of a teutonic disposition)! It is interesting that there is a common view in the lambic community that spontaneously fermented brews derive some of their raunchiness from what is effectively underpitching. But even there, the break is usually fermented and the primary is supposed to be open.

 

[muckanic]

And yet more. This is something I harvested from the ATIB digest many moons ago, and is quite an informative read:

Date: Sat, 31 Aug 1996 02:50:32 +1000
From: Charlie Scandrett <[email protected]>
Subject: Ester Identification & Control

This is a summary of what I have found so far,

ESTER CONTROL.
One of the problems with the ester thread recently in the HBD was the usual old
fallacy of treating the whole class as though it had the same properties,
this is the logical fallacy of summation & division. I have tried to isolate
factors affecting different esters.
Esters are produced by yeast metabolism with the acyl CoA enzymes, from
carboxylic acids (usually aliphatic (fatty) acids) and alcohols.

R1CH2OH + R2COOH = R1CH2OOCR2 + H2O

The different abundance of different fatty acids and alcohols produces different
esters, some of which are desirable in ale styles and some of which are
considered off flavours.

Major Esters in Beer.

ESTER Flavour-Aroma Typical. Flavour Thres.
Ethyl acetate Solvent, fruity, sweet 8-48 ~25
2-Butyl acetate Paint thinner, plastic,& 2 12
glue,
2-Methylpropyl acetate Banana, sweet, fruity. 0.01-0.025 1.6
2-Methylbutyl acetate Banana, estery, solvent,& 0.6-4 1.2
sweet.
3-Methylbutyl acetate Banana, estery, solvent,& 0.6-6.6 ~1.05
(this is Isoamyl acetate) apple-like.
2-Phenetyl acetate Rose, honey, apple, sweet. 0.05-2 ~3.4
Ethyl Propanate 0.03-0.2 ~5
Ethyl Butanoate Papaya, buttery, apple,& 0.04-0.2 0.4
perfumy.
Ethyl 2-Methylbutanoate Sweet, fruity, grape,& 0.001-0.015
0.007-0.2
artificial candy.
Ethyl 3-methylbutanoate Fruity, grape, sweet,& 0.005-0.04 0.018
isovaleric.
Ethyl hexanoate Apple, fruity, aniseed, & 0.07-0.5 ~0.19
sweet.
Ethyl octanoate Apple, sweet, fruity. 0.08-1.5 ~0.6
Ethyl decanoate Caprylic, fruity, apple,& 0.01-1.0 ~1.0
solvent.
Ethyl dodecanoate Caprylic, estery. 0.015-0.6 ~2.75
Ethyl tetradecanoate Caprylic, vegetable oil. 0.4 >2.0
2-methylbutyl 2-methyl- 0.07 0.05-0.6
propanoate
3-Methylbutyl hexanoate Caprylic, fruity, solvent,& 0.001-0.21 0.9
perfumy.
3-Methylbutyl octanoate Fruity, hot (spicy), orange, 0.008-0.42 2.0
pear-like.
Geranyl 2-methyl- Floral-pleasant(from hops) 0.025-0.15 0.45
propanoate
Methyl 4-decanoate Floral (from hops)
Methyl 4,8-decadienoate Floral (from hops)


Since Acetic Acid is the most abundant acid, and since Ethanol is the most
common of alcohols, it is not surprising that the Acetates are the most common
esters, Ethyl Acetate in particular. Fortunately it also has the highest
flavour threshold and levels can be controlled. The Ethyl Esters are called
the "Apple Esters" for obvious reasons and are generally undesirable. Ethyl
Acetate and 2-Butyl Acetate exhibit "solvent" flavour/aromas.. As Ethanol
will always be in abundance, they must be controlled in other ways. Wort
composition and oxygen seem to be the most important control parameters for
the Ethyl esters.
The Methyl** Acetates are called the "Banana Esters", also for obvious
reasons, and are often prized aromas in some styles. Because acetic acid is
always available, levels of these depend on the intracellular pool of acetyl CoA
enzyme concentration and the occurrence of the corresponding higher (fusel)
alcohols:
2-Methylpropanol
2-Methylbutanol
3-Methylbutanol
All other esters capable of reaching flavour or aroma threshold, and for
which these alcohols are precursors, are described as "fruity, sweet".
Control of these higher alcohols can thus yield a pleasant ester profile.
2-Phenyl Acetate is called the "Rose Ester", for its rose-like aroma.


Factors Affecting Esters.

*HIGH WORT densities promote esters, raising 10P to 20P = total esters x
3to8 times. This can be somewhat offset by increased and continued aeration.
The ratio of carbohydrates to amino acids is not important, and ethyl acetate is
unaffected by amino acid concentration.
*AMINO ACIDS. Excess amino acids will stimulate fusel alcohol production.
This can raise the "Banana Ester" level without affecting Ethyl Acetate.
These fusel alcohols are also raised by increased cold trub residue, but the
suppression of Acetyl CoA by trub availability balances out any increase in
the Acetates in this case. ("Bananas" are Methyl** Acetates). The "Rose
Ester", 2-Phenethyl Acetate actually decreases with increasing AAs, but
Ethyl Hexanoate increases. More than 30 minutes of mash time spent between
45-55C will ensure excess amino acids these days.
*FATTY ACIDS. Level of unsaturated fatty acids >C15, especially Linoleic
acid (C18:2), reduces all esters but in particular, Acetate esters. The
level required for significant reduction is >20 ppm, but levels dissolved in
wort that high would lead to staling problems. However, retaining >50% of
cold trub haze (which is > 30% long chain lipids) will make available some
of the necessary level during growth phase. Yeast apparently absorbs the
attached lipid droplets by the gooey hug method, a bit like amoebas having
sex! Excess trub can be removed by racking or flotation before completion
of fermentation thus avoiding staling. The process seems to be the
redirection of Acetyl CoA enzyme to yeast growth. The levels of *medium*
chain fatty acids actually promotes the formation of their corresponding
esters, eg Ethyl Hexanoate.(aniseed, apple) Poorly lautered wort will have
higher medium chain lipids in solution. Whirlpools remove fatty acids
uniformly, but flotation tanks have little effect on the remaining medium
chain fatty acids. Flotation tanks reduce the staling and Ethyl Acetate
suppressing long chain FAs significantly.
*OXYGEN. This is not the biggest effect! In the presence of O2 at the growth
phase, saturated fatty acids are biosynthesised to unsaturated fatty acids
and the principal yeast sterols; lanosterol, ergosterol and zymosterol.
These have chains >C15 and suppress the Acetate esters in particular. Once
wort oxygen has been utilised, precursors to these sterols become esterfied
because levels of Acetyl CoA increase. Decreasing O2 levels from 6ppm to
3ppm has been shown to increase total esters by up to 50%, however such low
levels are unusual. Above 6ppm, O2 has little effect. However a fermentation
with all cold trub left in during growth phase would have a similar total
ester level to a clarified, but well aerated, ferment. The ester profile of
a cold trub rich *and* well-aerated cool ferment may well be too low for
some styles. This need for balance between O2 and Linoleic Acid (C18:2)
concentrations leads to some ferocious anecdotal arguments among homebrewers
which are probably deleterious to their beer.
*DIATOMACEOUS Earth. The addition of DE to a trub-clarified fermentation at
4% wet volume will suppress total esters to a similar level to leaving most
cold trub in. DE stimulates fermentation by providing nucleation sites for
CO2 without increasing lipids. However Ethyl Acetate is disproportionately
reduced, leaving the "Banana Esters" and the "Rose Ester" largely unaffected!
*TEMPERATURE raises all esters, (there are reported exceptions) a 15C
increase in fermentation will usually increase total esters x ~2, however
Isoamyl Acetate(banana) and Ethyl Octanoate( sweet fruit) peak at 15C, while
Ethyl esters generally increase uniformly with temperature. The effect of
temperature on ester profile changes with Linoleic Acid (C18:2)
*PRESSURE. The formation of Acetate esters is substantially reduced by
increasing hydrostatic pressure. Reduced pressure stimulates acetate
formation whereas the Ethyl Esters reach a maximum around atmospheric pressure.
*YEAST Strain. The ester profile is a characteristic of each strain, with
some stains varying particular esters by as much as 100%, under the same
conditions. Ale yeasts (S.Cerevisiae) produce considerably more esters, even
when fermented at the same temperature as lager yeasts.(S.Uvarum)
*PITCHING Rate. A twofold increase in pitching rate will very slightly
selectively suppress Ethyl Acetate. Above that, other esters are also
slightly affected.
*LAGERING. Under normal conditions, only small changes in ester levels occur
during cold storage.
*pH. Has been shown to have little effect on ester production.


Summary of Effects on Ester Levels.

(! = important but variable, + = increase, - = decrease)
Ester Yeast Gravity Temp Pressure Amino N Lipids +O2 +DE
Ethyl Acetate !!! +++ +++ -- 0 -- --- ---
(solvent, fruity)
Ethyls-* * !!! +++ +++ -- 0 - 0 --
(apple +)
** -Acetates !!! + + -- ++ --- -- 0
(bananas)
2-Phenethyl- !!! - ++ - 0 0 - 0
Acetate (rose)

Basically, yeast selection will be your primary method of controlling the
ester profile of your beer. Desirable notes can be enhanced or protected, while
undesirable notes can be suppressed, using selective techniques of wort
production and fermentation control.


References.

Malting and Brewing Science-Vol2- Hough, Briggs, Stevens & Young.
Brewing Science -Vol 1- J.Pollack
European Brewery Convention--15th Congress-1975-Control of Ester Formation....
The Influence of Trub on Fermentation and Flavour Development---Brauwelt
Free Fatty Acids in Wort & beer---Klopper, tuning and Vermeire
Principals of Brewing Science--G. Fix
Volatile Compounds in Foods and Beverages---Henk Maarse
Food Science Handbook--Nick Light


regards,
Charlie (Brisbane, Australia)

Charlie, are you listening by any chance?