effects of stirring a starter

[scpizza]

Stirring a starter will result in more vigorous fermentation and higher rise in the jar.  The question is what's the primary driver of this?

1) Is it the oxygenation fueling increased metabolism (and strengthening gluten)?
2) Is it the redistribution of nutrients fueling increased metabolism
3) Is it the mechanical development of the gluten just giving the appearance of increased activity by trapping more gas?

I vote #1 as the primary factor, but am curious what others have to say.

[Crider]

I'd say it is number 2, since the yeast is anerobic and that the yeast doesn't have any means of travel. Read this:

http://www.thefreshloaf.com/node/10375/lactic-acid-fermentation-sourdough

[scpizza]

That's a good article, but I don't draw the same conclusion as you did.

Yeasts (and some bacteria) are in fact facultative anaerobes so with oxygen available they produce 18x as much energy from a sugar molecule as without oxygen.  That's a high hurdle to beat.

If #2 is the primary factor, then a stir would have to provide all the organisms in the starter access to far more new sugar molecules than it provided the facultative anaerobes access to new oxygen molecules.

Hard to predict in theory, there are so many factors in play.  Would be easy to test if had a sealed CO2 or N2 filled chamber to work with.

[dmcavanagh]

I seem to remember reading that the stirring oxygenates the culture which activates it. So i guess i'd agree with #1.