The effect of brewing temperature on flavor components in cider
dennis...@comcast.net
In the book Yeast: The Practical Guide to Beer Fermentation the authors, Chris White and Jamil Zainasheff, include a chart on page 96 that compares the flavor components of two beers from the same wort fermented with the same yeast, White Labs WLP001 California Ale Yeast, but brewed at two different temperatures. One batch was maintained @ 66F (19 C) and the 2nd batch @ 75 F ( 24C). After fermentation the two beers were analyzed by gas chromatography. While the amounts of ethanol, 1-propanol, total diacetyl, and isoamyl alcohol were roughly the same in both batches there was a huge difference in the amount of acetaldehyde: it was 7.98 ppm when fermented at 66 F but 152.9 ppm when fermented at 75F!! This would make a huge difference in flavor of the beer because the perception threshold for acetaldehyde is only 10 ppm.
(Other flavor components were also different: ethyl acetate was 50% higher @ 33.45 ppm at 75 F but that may be a minor problem because the flavor threshold is only 30 ppm. The total 2,3 pentanedione was 30% lower @ 3.17 ppb but that is not a problem because the perception threshold is 900 ppb.)
I realize that cider is usually fermented with wine, not beer, yeast and the components of the wort are very different, but does anyone know whether:
1) The wine yeasts used in cider fermentation would perform in a similar way?
2) Would the high level of acetaldehyde be reduced significantly (hopefully below the perception threshold) by aging and if so how long should the cider be aged and at what temperature?
3) Is minimizing the level of acetaldehyde the primary reason that Andrew and other authorities recommend fermenting cider at a cool temperature ~ 60 F?
4) Are there other flavor components in cider that would be different if the cider is fermented at a high temperature?
5) Are any of the flavor components produced at a higher fermentation level beneficial to the taste of cider?
Dennis Waller
greg l.
the end of fermentation, it seems like the second batch had
significant oxidation issues. Acetaldehyde and ethyl acetate are both
the result of exposure to oxygen. Acetaldehyde is a normal step on the
path to alcohol production by yeast, but there shouldn't be much left
at the end of fermentation. When red wine is fermented on skins in
open vats,and is fermented at higher temps, it smells quite strongly
of acetaldehyde yet afterwards smells fine.
Greg
Dick Dunn
"fermentation temperature" here. The actual beer-related results are
about two different fermentation temperatures. And cider, of course,
is not brewed, which is why the results might be of interest.
--
Dick Dunn rc...@talisman.com Hygiene, Colorado USA
dennis...@comcast.net
Dick
Please explain your distinction between "brewing temperature" and "fermentation temperature". The book states the two batches of innoculated wort were held at two different temperatures.
Dennis Waller
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Andrew Lea
necessarily have any clear cut answers. But I will try. For those who
are not interested in this level of technical detail - look away or
delete now!
First I agree with Greg that acetaldehyde levels of 150 ppm are
stonkingly high and perhaps imply some sort of oxidation outside of the
normal fermentation process. Normal acetaldehyde levels during
fermentation are in the region of 25 - 50 ppm for wines and ciders and
maybe lower for beers (I just checked in Briggs et al "Brewing" - a
classic and authoritative tome from the Brewing School at the University
of Birmingham UK - which quotes 20 ppm max). Acetaldehyde is not some
sort of flavour by-product; it is central to anaerobic metabolism by
yeast and every molecule of alcohol that you drink will have been a
molecule of acetaldehyde at some point during fermentation. So the
acetaldehyde is constantly being turned over and reaches an equilibrium
level. There is no reason to expect wine, beer or cider yeast to perform
much differently in the *fundamental* way that they synthesis and
transform acetaldehyde (though its perception as an 'off-flavour' is
probably more marked in beers than in wine/cider because of matrix and
pH differences. Likewise diacetyl and pentanedione are not generally
regarded as off-flavours in cider or wine).
However, strain, nutrient and temperature differences can have a marked
effect on its production, as can the level of SO2 (not used for beer
fermentation, where wort boiling replaces it, but generally used for
cider and wine). Oddly this connects with a thread not long ago about
SO2 where I mentioned that the presence of SO2 actually induces the
yeast to generate more acetaldehyde to compensate for what is bound to
sulphite. There is some data on strain, nutrient and temperature
differences in this paper from my website here
http://www.cider.org.uk/ciderbind2.pdf (370K PDF) - go to Table 6. This
shows that acetaldehyde levels (in that study) reduce as fermentation
temperature increases. But remember all those fermentations were
sulphited as is standard practice. Briggs remarks that high acetaldehyde
levels in brewing can be induced by excessively high fermentation
temperatures (he does not enumerate). So in this case it is possible
that the effects in beer compared to wine/cider are different. I do not
know any direct comparative data.
Acetaldehyde is quite reactive and so in theory and practice can be lost
on anaerobic ageing, especially by reaction with alcohols to form e.g.
dioxolanes. Also it will bind with sulphite (one reason we add it) so
that although the acetaldehyde is still present it is bound and
sensorially inactive. If there is any chance of oxidation, acetaldehyde
levels will almost certainly rise (that is a chemical reaction mediated
by hydrogen peroxide produced by polyphenol oxidation in air). If MLF
takes place, the acetaldehyde level will probably fall. Practically
speaking, the levels of acetaldehyde normally encountered in well made
ciders and wines (let's say up to 50 ppm) are not regarded as an issue
despite being above their sensory threshold (after all if nothing was
above its sensory threshold the cider might have no flavour!). Of course
at higher levels and in the absence of SO2 a 'sherry' note becomes evident.
The reason for recommending cool cider fermentation has nothing to do
with acetaldehyde. The same advice is often given for white wines and it
is generally because ester production and retention is higher at low
temperatures while the accumulation of some fusel alcohols is less.
(That is considered to give a more desirable flavour balance). However,
this is hugely dependent on yeast strain and nutrient status so it is a
sweeping generalisation. Also a lower temperature (< 15C) may favour the
growth of non-Saccharomyces yeast whose additional flavours some of us
value (up to a point!). But not all cidermakers agree and some large
commercial cidermakers do ferment at 25C because they believe that gives
them what they want. Maybe they prefer fusels over esters. Here is
another paper you may like to read which mentions some of these things
inter alia
http://www.scientificsocieties.org/jib/papers/2006/G-2006-1012-432.pdf
(400 KB PDF).
I hope this answers some of your questions without going into excessive
detail.
Andrew
On 09/02/2011 19:28, dennis...@comcast.net wrote:
> In the book _Yeast: The Practical Guide to Beer Fermentation_ the
> dennis...@comcast.net <mailto:dennis...@comcast.net>
Dick Dunn
> Please explain your distinction between "brewing temperature" and "fermentation temperature". The book states the two batches of innoculated wort were held�at two different temperatures.
OK, they were talking about beer. "Brewing temperature" would be the
temperature at which the wort is cooked (brewed), which would normally be
a bit over 100 �C ("over" because it's got sugar in it). It's not
relevant because beer is always brewed at boiling (unless you're brewing
at altitude, but that's an entirely different experiment).
But in particular, it's not relevant to us because cider is not brewed.
(one hopes!)
"Fermentation temperature" is the temperature at which the beer is held
during fermentation (after pitching yeast). That's what the article was
about, and that might be relevant to us in terms of what the yeast does
and produces.
Claude Jolicoeur
> But in particular, it's not relevant to us because cider is not brewed.
> (one hopes!)
French books on cider making during the winter, and they sometimes
write about "Brasser" or "Brassage" of the cider - which is the French
word for brewing. I'll have to check this again to figure the exact
context in which they used it.
Claude
dennis...@comcast.net
Andrew
Thank you very much for your detailed and very informative answer to my questions. I have downloaded and will carefully read the two articles you mentioned.
However, I have one followup question. Since I only make cider for myself and my family, I often purchase pasteurized sweet cider made by a large Washington State apple processor,TreeTop, during those times of the year when I can not purchase freshly pressed cider. Since the TreeTop product is pasteurized, I have not added any SO2. You mention that acetaldehyde "...will bind with sulphite (one reason we add it) so that although the acetaldehyde is still present it is bound and sensorially inactive." My question: Is there any taste benefit of adding SO2 to the pasteurized sweet cider before fermentation?
Dennis Waller
Andrew Lea
> My question: Is there any taste benefit of adding
> SO2 to the pasteurized sweet cider before fermentation?
The primary function of SO2 added before fermentation is anti-microbial.
So if the juice is already pasteurised and you add a cultured yeast
inoculum it's not necessary. If you are worrying about acetaldehyde, I'd
say the normal levels at end of fermentation (25 ppm or so) will not be
an issue, just part of an acceptable flavour profile.
But after fermentation that initial protection from pasteurisation will
have been lost. So it may be wise to add some SO2 before storage to
prevent both microbial attack and oxidative generation of acetaldehyde
and other adverse flavours.
Andrew
--
Wittenham Hill Cider Pages
www.cider.org.uk
Trevor
"problem' we in NZ have ( and I presume in Aus) is that the summer is
still in progress at harvest time so the ambient temperature at
fermrentation is approx 20C. Washing milling and pressing is much
nicer though above sub artic temperatures! I am considering a heat
pump to cool the cider barn down to 12C for the time before autumn/
winter temps kick in. This year is esp bad today is 30C in the orchard
and the Tom Putts are ready. I had a real shock as we are one month
advanced over last year. Still it was nice to show Rose Grant around
in the sunshine. Cheers Trevor
>
> I hope this answers some of your questions without going into excessive
> detail.
>
> Andrew
>
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