Long lTechnical post 3
Daniel Wing
Amylase digestion of this damaged starch provides sugar for fermentation
and produces dextrins, a class of polysaccharide that is quite
hygroscopic.
**
See comment No2: lactobacilli and yeast rely on the amylase of the grain
as they donąt have starch degrading enzymes. A Spanish group has looked
for the development of maltodextrins during sourdough fermentation: as
lactobacilli and yeasts donąt like the oligosaccharides, they accumulate
during fermentation. The Spanish (C. Collar and M. Martinez-Anaya in
Valencia, Spain) think that maltodextrins may delay bread staling, though.
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because that enzyme (PHYTASE) is most active in dough between pH 4.3 and
4.6, prolonged fermentation with mixed cultures (an acid medium) will
**
It is true that the enzyme is most active IN DOUGH between pH 4.3 and 5,
however, the reason is not optimum enzyme activity at this pH, but the
fact that CaMg-Phytate is insoluble and thus not available for enzymatic
cleavage at a higher pH. (The first work during my diploma thesis was to
look for phytase enzymes in lactobacilli from sourdough. After 8 weeks, I
figured out that there is none, and shortly thereafter it became clear
that both wheat and rye have sufficient phytase activity, all it takes is
some acidification).
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I chose to write "natural leaven" because it is less awkward than "mixed
ferment cultured from the environment and sustained with repeated
inoculation."
**
“Sustained with repeated inoculationł is better than anything I was
writing to say the same thing. Cultured from the environmentł is certainly
true - L. sanfranciscensis and the yeasts must come from somewhere - but
somewhat misleading, as these organisms most probably do not originate
from the grain, or the flour (Marco Gobbetti, whom I mentionned earlier
has been looking for L. sanfranciscensis on all kinds of Italian wheat
flours, and he has not found any. In every Italian dough “sustained with
repeated inoculationł youąll find L. sanfranciscensis to be the dominating
species, though. No other scientist has been able to isolate L.
sanfranciscensis from any other source than sourdough, but all sourdough
“sustained etc.ł Contain this organism as the dominating flora. A possible
source may be the humans: there are all kinds of lactobacilli thriving in
the mouth, the intestines, etc. Hammes met a South African Microbiologist
who claimed to have isolated L. sanfranciscensis from the teeth of
pre-school children. The data is not published, so I donąt know what
science is behind this claim. But, whereever L. sanfranciscensis comes
from, it most probably does not come from the flour. (Thats comment No4)
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Natural leavens are not all the same. Not only are there many strains of
yeast and bacteria that can form them, we need terms in English for the
various stages of natural leavens.
**
One may think of all the “sourdough stagesł as just a piece in a infinite
chain of repeated inoculations. Some sourdoughs are quite close to
infinity, as far as the generations go. You certainly know Carl Griffith
sourdough (claimed to have survived since the days of the Oregon Trail);
the dough weąve been working with, Böcker Reinzucht Sauer, a rye starter
that thas the reputation of being one of the best rye starters available
(Spicher says so, we do, and the Spanish group has been working with it as
well), is well above 50 yeast “oldł. Then, the definition of e.g. “three
stage sourdough processesł does make no sense. What makes is fascinating
is that the microbiology of Böcker Reinzuch Sauer HAS NOT CHANGED in the
past 30 yeast, i.e. since people started to do microbiology with the
dough. There are two strains of L. sanfranciscensis, and one yeast, C.
milleri. The “modelingł I mentioned in comment No1 was done with these
three organisms. Remarkably, the two strains of L. sanfranciscensis
reacted almost identically on changes of pH, temperature, etc. Then, the
definition of e.g. “three stage sourdough processesł does make no sense.
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This selection leaves it (COMMERCIAL YEAST) specialized for a narrow range
of fermentation characteristics that favor rapid gas production over
flavor production or other possibly desirable qualities (resistance to
bread spoilage, for instance).
**
This could be also said for sourdough lactobacilli and yeasts: As the
dough is continuously refreshed, those strains are selected that grow
fastest in dough. This is probably a much more harsh and effective
selection than what is done for the bakerąs yeast. Fortunately, what is
good for the sourdough lactobacilli seems also to be good for bread
quality (There are other microorganis in fermented food that require the
man-made habitat: e.g. Tetratenococcus halophilus growing only in soy
mashes, and Oenococcus oeni, occuring in wine only.) What is important, is
that as soon as you change your parameters, you may change the microflora.
E.g., if the dough is fermented at 33 instead of 28°C, yeasts will drop
out, and above 37 - 38°C, the flora will change altogether, with
thermophilic lactobacilli dominating. See comment No1.
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The yeast and bacteria in natural leavens are considered native or wild
because the cultures are started with organisms recovered from
environmental surfaces,
**
The fermentation starts with flour microorganisms, but - see comment No4 -
the sourdough lactobacilli and yeasts do probably not originate from the
grain. And later: the organisms have been refined by thousands and
thousands of sourdough - refreshments, much more effective than any
microbiologist of food scientist could ever be. (Besides, we know what
kind of organisms do grow in sourdough - but how flavor production takes
place, and which fermentation products delay bread staling is largely
unknownm - so other than gas production, I could not think of a property
of lactobacilli in which to select a strain. And gas production, as youąve
rightfully pointed out, is certainly not the right criterium.)
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The conditions under which a culture is developed and then maintained can
select out strains of yeast and bacteria that have special
characteristics, and the typical yeasts present in the air and soil in
different locations also vary somewhat in their properties and their
interactions with lactobacilli. This kind of co-evolution makes some
natural leavens remarkably stable when regularly maintained. The more
regular and consistent the maintenance, the more predictable the rising
power, microbiological composition, acid balance (acetic/lactic) and acid
production will be.
**
This is important (although I donąt think that the yeasts from air and
soil do matter). But the consistency in maintenance is crucial (one is
allowed to err to one side or the other from time to time, though).
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continued in next post-- DCW
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Dan Wing
Wag...@connriver.net