Growth of Baking Yeast

Mick mick at
Fri Sep 12 04:27:20 EST 1997

Kenneth Sole wrote:
> > > I have noticed that if the first starter takes, say, 28 hours to
> > > double, all the following stages will take (pretty close to) that
> > > same amount of time.
> > >
> > > This conflicts with my intuition... (snip)

Marc R. Roussel replied:
> Note that this is just Malthusian growth. (snip)

Timothy J. Kordas additionally replied:
> Marc answered the question correctly. The "rate of rise" of the dough
> *does* accelerate: (snip)

There seems to have been a misunderstanding which I feel compelled to
clear up.  When you read Kenneth's original message, you have to make
the assumption that when the dough is "refreshed", the carbon dioxide
that made it rise is released.  The dough starts off "flat" at each new
stage.  You make this assumption not through any knowledge of baking,
but because of an additional assumption that Kenneth is intelligent and
has made an honest observation that conflicts with his intuition, and
that he would not have bothered this newsgroup with a description of
everyday Malthusian logistic growth.  Anyway, when you mix a load of
fresh dough into risen dough, it seems obvious that the gas would be
squeezed out of the already risen dough, n'est pas?

In other words, reading between the lines ever so slightly, Kenneth is
saying that the rate of rise of (initially flat) dough is <not>
accelerating, even though his intuition told him it should.  This
observation requires an explanation.

Marc and Tim do not seem to make the assumptions I referred to above,
and proceed to treat us to some elementary mathematical expositions
which are made redundant by Kenneth's intuition.  Thanks boys; it's good
to see you are keen, and I hope you continue to work it out with a
pencil. (Ouch!) 

A plausible answer to the problem has now been provided by Gene Kidman
(this thread), who says the growth of yeast in dough is limited by the
low abundance of sterols, which yeast cannot make for themselves in the
anaerobic conditions found in a lump of dough.  A simple experiment
could settle the matter.  Add some ergosterol too your dough, Kenneth,
and see what happens.

Michael Pocklington

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