Growth of Baking Yeast
Timothy J. Kordas
tkordas at gsbs3.gs.uth.tmc.edu
Thu Sep 11 15:53:33 EST 1997
Marc R. Roussel replied:
> > Note that this is just Malthusian growth. Since gas evolution
> > (which determines the macroscopic doubling time) is proportional to the
> > population, your dough doubling time should be approximately constant
> > provided the yeast are always well fed.
mick at blankley.prestel.co.uk wrote:
> Well, may I point out that since the rate of rise of the dough is
> proportional to the number of cells per unit volume of dough, then the
> rate will only be constant if the number of cells per unit volume stays
> the same. [ ... ]
> So the rate of rise of the dough should accelerate. IF it does not, an
> explanation is required, as Kenneth points out.
Marc answered the question correctly. The "rate of rise" of the dough
*does* accelerate: the "rate" is measured in units of volume per
unit time. He only discussed the *doubling* time.
Take a simpler example: a doubling time of 1 hour.
t P dP/dt d2P/dt2
0 1 - -
1 2 1 -
2 4 2 1
3 8 4 2
[ . . ]
10 1024 512 256
11 2048 1024 512
By looking at things in terms of doubling you simplify the expression:
you are expressing things in terms of the base-2 logarithm.
This being an exponential growth process, the rate is increasing at an
increasing rate ... it *is* accelerating. And as Marc pointed out the
purpose of the additional flour to make sure that nutrients do not
become limiting ... if you wanted to keep this culture going in
exponential phase for a long time you'd soon have to add *much* more
flour.
-Tim
--
Timothy J. Kordas
UT-Houston Medical School
Dept. of Pharmacology
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