[Sca-cooks] German Breads

[Terry Decker]

> Commercial yeast are grown in molasses, they are adapted for using
> the easy food they get from sugars and don't do well in the long run.
> The wild yeasts are adapted to a different food source (the grain).
>

What's your source for wild yeasts growing on grain?

To my knowledge, all yeasts use sugars for food.  The yeasts we have been 
discussing all feed on simple sugars and can not directly feed on grain. 
They can't even directly use the primary sugar in the molasses, sucrose. 
However, in commercial manufacture, the initial prue yeast infusion is fed 
on molasses malt to kickstart the process.

Commercial yeasts have been bred to produce varying quantities of alcohol 
and CO2, but they eat the same sugars as wild yeasts of the same species.

> There has been a lot of argument over this in the sourdough community
> and the scientific arena. However, at least a few of the
> microorganisms (and possibly the yeast that occurs naturally in
> flour) appear to produce amylase (a starch degrading enzyme) and
> maltase (an enzyme that breaks down complex sugars to simple sugars).
> Though it is possible that these enzymes are also of plant origin and
> may occur in the grain naturally, they definitely are produced in the
> grain if it is germinated (that's part of the reason for malting
> grain, to make these enzymes available for mashing and brewing).
>

Grains have an outer coating bran which consists of a number of things that 
can't be converted to sugars.  The outermost layer is called the aleurone 
layer consisting of a complex protein, aleurone.  Among the things in the 
aleurone are hydrolytic enzymes and the triggers for releasing them, 
including diastase (alpha amylase).  So there is no question that the 
enzymes in question are of plant origin and occur naturally in grain. 
Comparisons of fermentation between high and low alpha amylase flours 
demonstrates that some of the grain enzymes are released in fermentation. 
That almost certainly enhances the yeast enzyme production, which tends to 
be rather slow.

During germination, gibberellin hormones trigger the release of the enzymes 
to break down the starch in the endosperm, so that it can be used by the 
plant embryo, which is why malting works the way it does.  Malting is 
usually associated with beta amylase production.

If anyone is interested, Lallemand (a yeast manufacturer) has quite a bit of 
information on measuring and standardizing enzyme levels in flour at 
http://www.lallemand.com/BakerYeastNA/eng/PDFs/LBU%20PDF%20FILES/1_15ENFL.PDF . 
One tidbit they mentioned (that I vaguely remember from long ago, that means 
more now than it did then) is that most breadmaking flours have .25 percent 
malted barley of wheat flour added.  The enzymes are ready to go and the 
starch conversion has already started in these flours (and it should be 
noted on the label).  Such a flour should give a nice kick to a sourdough 
starter.

>>nor does it usually grow on the
>>grain kernals.  If they did, they would attack the flour immediately after
>>milling.
>
> Yeast require a relatively large quantity of water to survive in
> their active state, there is not enough moisture for this to occur in
> the grain or the resulting flour. Even with relatively "green" grain.
>

Water is a requirement of the hydrolytic enzymes that produce the sugars on 
which yeast feed.  If it was simply that yeast need water, then they should 
be cheerfully chomping away on the rice in every rice paddy in the world. 
Oh, and that pesky bran layer that gets in the way.

>>Yeast spores settle on the grain and are processed through with
>>the wheat into the flour, which is why you can cover a bowl of starter 
>>with
>>plastic and it will still ferment.
>
> Yeast are anaerobic organisms, they do not require oxygen except for
> reproduction. While you feed a starter, a sufficient quantity of
> oxygen is usually mixed into the slurry to enable the synthesis of
> protein and the budding of new yeast cells. Once they enter the
> fermentation stage, the yeast can survive just fine without oxygen.
>

It is immaterial to this argument whether they are anaerobic or not.  The 
point is that there are yeast spores that go through flour milling and are 
in the flour we purchase.  You can work in a totally sterile environment, 
but if you make a starter in that environment with off the shelf flour, it 
will likely be "alive!"

BTW, aerobic fermentation promotes yeast growth while anaerobic fermentation 
increase the output of alcohol and CO2.

<clipped>
>>I have encountered an interesting statement that I have yet to check out,
>>that the yeast in San Francisco sourdough is now named Candida humilis,
>>previously C. milleri, and originally identified as Saccharomyces exiguus.
>
> Again, genome sequencing needs to be done to determine if it is a
> unique species, I'm not too hung up on that part of it really. It may
> be unique, it may not. I think the difference in results that are
> achieved have more to do with the way the starters are grown and
> maintained than anything else.
>
> Dragon

You don't consider the Stanford Yeast Genome Database extensive enough? 
Usually, it's a problem of finding the right paper.

Checking Doctor Fungus shows C. humilis, C. milleri, and S. exiguus as 
seperate species and they still appear that way in some recent papers.  It 
may be that there is a move afoot to consolidate them taxonomically, but 
that hasn't occurred, as yet.

Understanding the particular yeast/lactobacilli combination of a given 
starter is a key to optimizing the maintanence of the starter.  Also, it 
might make it possible to seed and maintain starters with specific 
characteristics.

Bear