From: delwiche@sunflower.bio.indiana.edu (Charles Delwiche)
Subject: Re: sourdough ecology clarification
Organization: Biology, Indiana University - Bloomington
Date: Fri, 28 Aug 1992 19:59:58 GMT

In article <1992Aug28.113031.15118@hemlock.cray.com> dadams@cray.com writes:
>In article u4@usenet.ucs.indiana.edu, delwiche@sunflower.bio.indiana.edu (Charles Delwiche) writes:
>|Just a quick corection:  I stated, or implied, somewhere along the
>|line that yeast produce amylase, the enzyme that digests starch and
>|breaks it down into sugars.

>|Sorry if I confused anyone.

To this David Adams wrote:
>
>Well this gives me an added point of confussion, since by my understanding,
>which may well be wrong as I am a layman here, the grains do not release
>amylase until the process of germination begins.

I probably should have just stuck with my original argument, but now
that I have gotten everyone, including myself confused, I went and
looked it up.  The enzyme in question, alpha-amylase, is apparently
indeed not produced by _Saccharomyces_, either by _S. exiguus_ or _S.
cerevisiae_.  David Adams is right; the amylases in grains are not
generally released until germination has begun.  At least this is what
one is always taught.  One makes malt by taking barley, moistening it,
letting it go about three days into the germination process (until the
root it just beginning to emerge), then killing the sucker by roasting
it in an oven.  Grind the malt up with a rolling pin or a food
processor and you are ready to make beer (don't forget to do the
sparging and all that, and you might want to plant your hop plants a
bit before you start germinating the barley).

None the less, in the San Francisco sourdough process, amylase becomes
active without germination of the grain (Saunders, Ng, and Kline,
_Cereal Chem._ 49:86.  1972).  They incubated an *acidified*
flour/water mixture (pH 5.0) and found a marked increase in maltose
content.  I wonder if the acidification is essential?  It helps,
because it inhibits the microorganisms already present in the flour,
but it *might* also help activate the enzyme (I just don't know).  If
you tried to do this without acidifying the mixture you would end up
with a big fungal mycelium, or with a nice sourdough starter, depending
upon how lucky you were.  I think that the total amount of maltose
released is small compared to what you get in malted barley, where
almost the entire endosperm (what we eat) is converted to sugar.

So you can make sourdough without adding sugar because sugar is
produced during the development of the starter.  The lactobacilli
don't use up all of the maltose produced, so there is enough to add
flavor to the bread, and also help the crust brown nicely.  There are
also enough sugars other than maltose produced that _S. exiguus_ can
grow.

I don't know to what extent this applies to other kinds of sourdough.
I'll be looking into that when I have some time.












-- 
----------------------------------------------------------------------------
Charles F. Delwiche, Dept. of Biology        |"We admit no more causes...
Indiana University, Bloomington, IN 47405    |than such as are both true
                                             |and sufficient." I. Newton
Newsgroups: rec.food.sourdough