hist-brewing: Slow Ferment, what is fast, and nutrients

ulfin at mail.portup.com ulfin at mail.portup.com
Wed Jul 7 16:16:06 PDT 1999


(Sent this earlier to Nathi, but I meant to send it here.)

Nathi writes:
>The commonly held belief is that if you add a lot of yeast
>and have as quick a ferment (highest bubble rate) as possible you will
>produce better mead.

I don't think that's a "commonly held belief".  The high pitching
rate is for a quicker start, not a quicker fermentation.  The
former is desireable, the latter might not be.

If all you want is speed, raise the temperature and keep
bubbling oxygen through it throughout the entire fermentation
(the aerobic fermentation uses up sugars much faster than
the anaerobic stage, so it'll ferment out sooner).  Sure, you'll
probably end up with undrinkable cardboardy mead with plenty of
rotting cabbage esters and fusel alcohols, but just think of the
time you'll save.

>So what my post is questioning, is
>if the long held philosophy many of us have of more yeast and fast
>fermentation rate equals better mead, is actually FALSE (gasp).  (notice
>that I am questioning the common knowledge here, gasp-gasp!)

Again, I think this is a misunderstanding of the "long held
philosophy".  You're confusing quick starts with quick fermentation.

>One
>factor is definitely temperature since a vigourous ferment will raise the
>temperature of the mead, but this is probably not the only one since you
>can have a fast ferment AND a cool temperature by simply dropping the
>ambient temperature as I do with my meads.

Lowering the temperature will slow the yeast activity. Always. (Well,
between 32 and 120 degrees F, anyway.)  But this is not necessarily
a bad thing.  Even lager yeasts ferment more actively at higher
temperature; however, their products won't be as clean.

We want quick starts to stave off infection.  Fresh must is much
more susceptible to infection than must once it is active.   Once
you have a well-established colony of the happy beasties, outsiders
don't have much chance to cause problems.   We want to eliminate
the period during which the yeast is just waking up and beginning
to reproduce.

Look at it as two stages:

____Stage 1: Propogation (aerobic fermentation)___
Input: yeast                Yields: more yeast (a lot)
       sugar (a lot)                alcohol (a little)
       oxygen (a lot)               CO2

Then when there is a sufficient yeast colony (I guess the
cells have a board meeting to determine this, then send out
a memo), it moves on to the second stage:

____Stage 2: Fermentation (anaerobic fermentation)_____
Input: yeast                Yields: more yeast (only a little)
       sugar (not as much)          alcohol (a lot)
       oxygen (only a little)       CO2

If you have too much oxygen in the secondary fermentation,
it will oxydize the wine 'cuz the yeast can't use it up.

Also, the anaerobic fermentation is much slower (in terms
of gravity drop).  70-90% of your fermentation is during
the propagation stage, and that can occur in a couple days
or even just a couple hours.  The remaining 10-30% can
take weeks or years.

Shortening the propogation stage is also desireable for
production efficiency reasons.  During this phase the yeast
is using the food (your honey) to make more yeast and CO2
(both of which you discard as by-products) instead of alcohol
(your mead, do not discard).  If you have a large active
colony to begin with, you can bypass much of the propogation
phase and proceed to anaerobic fermentation.


Dan Butler-Ehle



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