SC - the late Ricardo Montalban????

[Philip & Susan Troy]

Depending on what you have put into the mix, if you induce fermentation with
Saccharomyces cerevisiae, at the end of two days, you should have burned up
all of the sugars which feed the fermentation.  The yeast goes dormant and
the acidic waste products begin killing the yeast.  It may take a while (6
days in the test I ran), but it does happen.  

One of the problems with standard bread yeast in starters is that S.
cerevisiae is not well adapted to acidic environments.  As the starter
becomes more acidic (sour), the yeast loses potency.  This isn't a problem
if you are going to use the starter once or twice, but if you want a
continuous starter, it's better to let nature provide the spores.

The sourness is not due to waste products from the fermentation.  Those
products are carbon dioxide and alcohol.  The sourness comes from the lactic
acid released by the growth of lactobacilli in the starter.  Since
lactobacilli growth is an aerobic process, once the air in the starter is
used up, lactic acid production stops, so does the souring.  As the starter
goes anaerobic, the fermentation actually picks up and continues until the
sugar runs out.  

By feeding the starter with water and flour when it goes dormant, you add
the sugars produced by the amylase reaction to feed the yeast and
lactobacilli and aerate the starter to refresh the lactic acid production.
Just letting the starter sit does not improve the flavor.  At room
temperature, my starters tend to cycle through active to dormant about every
12 hours, so they usually are feed morning and evening.

One are of confusion about starters are sponges.  A sponge is similar to a
starter (in fact some books call it a starter).  It is made by taking a
quarter to a third of the flour and water and combining it with the yeast
and sometimes the sugar in the recipe to form a dough.  This is allowed to
rest for 4 to 24 hours to improve the flavor and yeast growth.  The sponge
is then broken apart in the remaining liquid to spread the yeast when the
dough is made.  The sponge is completely consumed in the recipe, where a
true sourdough starter is recovered.

It's been over a year since I last used Herman (he is hiding in the
freezer).  After the Known World Costume Symposium, I think I'll bring him
out and resurrect him to play with Italian baking practices.

Bear  



> According to my resident expert on the subject, it's just 
> resting.  He says that
> when you first put the yeast in, it's like a primary 
> fermentation...it just goes
> nuts.  Now that there are not as many nutrients available, it 
> goes more dormant,
> having reached a kind of equillibrium.  The longer you let it 
> go, the more sour
> it will get, the sourness being a result of the waste 
> products from the
> fermentation.  This fermentation is still going on, but at a 
> significantly
> slower pace.
> 
> Hope this helps!
> 
> Kiri