From: watson@pioneer.arc.nasa.gov (John S. Watson - FSC)
Subject: Re: Simulating Fermentation?
Organization: NASA Ames Res. Ctr. Mtn Vw CA 94035
Distribution: na
Date: Wed, 16 Dec 1992 22:25:42 GMT

In article <1992Dec16.204701.6846@sernews.raleigh.ibm.com> murray@rocky.raleigh.ibm.com (Charlie Murray) writes:
>In article <1992Dec15.185053.9185@news.arc.nasa.gov>, watson@pioneer.arc.nasa.gov (John S. Watson - FSC) writes:
>|> I wondered: Has anyone ever simulated, on a computer (or otherwise)
>|> the dynamics of a fermenting carboy of beer?
>|> 
>|> From what I can see from the outside, down toward the bottom, 
>|> things are fairly calm.
>|> But near the top, there are all sorts of fabulous turbulents.
>|> 
>|> Is any net circulation inside the carboy?
>|> What would be the path of a yeast cell
>|> during the most active stages of the ferment?
>|> All sorts of questions pop into my mind.
>|> 
>|> Seems like this would be a fun program to write,
>|> while I'm slurping down my homebrews.
>
>On a macro level, you would expect there to be circulation of wort in the
>carboy due to the changing specific gravity.  This leads to an interesting
>question.  If the fermented liquid is lighter (lower SG), wouldn't all of the
>sugar laden wort sink to the bottom, away from a top fermenting ale yeast?

I was thinking the driving force of all the major currents and turbulents
in the carboy must be the rising  CO2 bubbles.    How do a bunch of little
bubbles rising straight up evenly cause all the little currents we see?

The yeast are just microsopic particles floating in the soap,
so I don't think they would have any effect, except maybe to change
the viscosity, and maybe the temperature.

I would like to know if 
there is any kind of net circulation, within the container.
I have in mind something like the simulations I've seen of thunder
storms.  Something like a donut shapped pattern rising  from the center
and folding over at the top and going down the outside and folding in
to the center again at the bottom (whew!).  
But looking at the current batch, all I can see is very random looking
currents everywhere (all that is visible is the sides).  

Other thoughts ... 
As it's going from a sugar/water solution to an alcohol/sugar/water
solution, does the viscosity change and how would that effect it?

> I would think the simulation would be quite complex, from what I remember
> from fluid dynamics, but I'ld also be interested in any work that has been
> done on the subject.

Yes, I also think it would be quite complex ... but ...
I think if the "turbulents" I see in the foment are not
really what the fluid dynamics people consider "turbulents",
(i.e., all the currents remain laminar), then there is a chance.

In a way, the model seems similar to a problem of a tank with liquid 
running into it from a outside pipe, and leaving from another.
Except all forces  are being generated internally, and there are no pipes.

Anyway, I guess I'll have to blow the dust off my fluid dynamics,
complexity theory, chaoic theory and  simulation modeling text books.

time to relax and have a homebrew, :-)
John

John S. Watson               watson@ames.arc.nasa.gov
#include <stddsclm.h> 

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