"wildeny" > wrote in message ups.com...
> Peter Reinhart posted this in his blog on 07/18/2006
> Please check this
Yeasts are facultative aerobes, meaning that they can switch, under
certain conditions, from anaerobic metabolism to aerobic. However,
it is quite likely that dough and starter fermentations are anaerobic,
and that stirring effectively speeds fermentation by repositioning the yeast
cells with respect to their nutrients, which are depleted in their nearness
by their metabolic activities.
Drying thin layers of batter, on the other hand, might possibly involve
aerobiosis, particularly inasmuch as the diffusion path is short, practically
allowing oxygen to reach the yeast cells. Under conditions of nutrient
depletion and oxygen abundance, yeasts may (when complementary
mating strains are available) merge and sporulate. Conceivably that
could be a mechanism in SD culture drying -- but unlikely because bread
yeasts tend primarily to be polyploid, and thus incapable of the orderly
reduction division required for sporulation.
Here is some discussion:
I have several (more than 6) times seen the false coming-to-life of reactivating
dry cultures mentioned by the subject author. Somewhere at r.f.s. I have
reported on that. It is my experience that there is no possibility of recovery
from it, other than back to square one. Possibly, as the author suggests, a
specific microorganism, e.g. * leuconostoc*, can be implicated.
I get depressed by statements like "yeasts need air to breathe", and "yeasts
love oxygen" as such statements imply microbiolical ignorance.