======================================================

PART 1 STARTS HERE

======================================================

From: wagons@connriver.net (Daniel Wing)

Subject: Long Technical Post 1

Date: 1998/05/25

Message-ID: <wagons-0301041020310001@port-1-26.wellsriver.connriver.net>

Organization: Cookeville Garage

Newsgroups: rec.food.sourdough

 

 

Some members of this newsgroup will remember that I have posted some of

the content of my correspondence with Michael Ganzle, a German sourdough

researcher. He has recently reviewed a proof of a book I have written

about masonry ovens and naturally fermented bread, and has commented in

detail. Those comments will interest those of you who are interested in

the science and technology of sourdoughs. This post and others that follow

are for you. If you ARE NOT linterested in the subject, stop here, and

save yourself from confusion and frustration.

In each section Michael quotes a sentance from the book, and then responds:

------------------------------------

"witness the profusion of instant yeast brands-- while the opposite is true³

**

I strongly appreciate the notion that the "time equals money equation³ is

not true for sourdough bread or any kind of other fermented foods-- wine,

soy sauce, cheese, vinegar, fermented sausage: they usually get better if

they are fermented for a long time (the definition of "long³ varies,

though, with the different foods).

-------------------------------------

"I triple it by mixing it with its weight of water and its weight of flour³

**

There is a microbiological explanation for the three stage sourdough

processes. Microbial growth can be divided in three stages. When the

organisms are transferred to a new environment (e.g. by refreshing a

sourdough that has been in the refrigerator), they take some time to

adapt; no growth occurs ("lag phase³). Once the organisms are familiar

with the new environment, they start to grow exponentially, meaning one

doubling of cell counts in a given time (generation time), so called "log

phase³. Eventually, the culture will become stationary, i.e. the organism

have run out of food, or are inhibited by the metabolic end products. For

effective sourdough fermentation, one needs a lot of metabolically active

cells. After three or more refreshments, the organisms will reliably start

to grow soon after inoculation and will produce enough carbon dioxide.

Things are different with yeast dough, though: there simply are so many

cells that these have to cough only once to raise the dough.

--------------------------------------------

"the time it was inoculated and to the temperature at which it is kept

than with the size of the inoculation.] Let's call this the second leaven³

**

Comment No1: Weıve been doing quite some work to figure out which factors

affect microbial growth in sourdough. Iıve done some work in vitro (which

is about to be published: Gänzle et al., Modeling of growth of

Lactobacillus sanfranciscensis and Candida milleri in response to process

parameters of the sourdough fermentation, Applied and Environmental

Microbiology, July 1998); and a colleague of mine, Markus Brandt, has

tried to figure out how my "model predictions³ work out during the actual

dough fermentation. Taken together, one can state the following:

A) The optimum temperature for sourdough lactobacilli is 32 - 33°C. At

37°C and 20°C, the generation time is twice as long.

B) At 39 and 15°C, the generation time is four times as long.

C) At 41°C and 4°C, no growth is observed.

For the yeasts, the figures are as follows:

A) 28°C(optimum growth)

B) 32/20 (double generation time)

C) 34/14 (fourfold generation time)

D) 35°C, 8°C: no growth.

So: if several refreshments are done above 32°C, the yeasts will drop out

eventually. The optimum pH for lactobacilli is 5.0 - 5.5 (which is the

initial pH of a sourdough with 5 - 20% inoculum), the minimum pH for

growth is 3.8 (they usually produce acid until pH 3.6 is reached).

Lactic or acetic concentrations donıt affect growth of lactobacilli very

much: this is the reason why the buffering capacity of the flour is so

important for the organism (a high buffering capacity in high ash flours

means that the lactobacilli produce much acid until the critical pH is

reached). It also means, that in doughs that are continuously operated

with a high inoculum (more than about 30%), youıll find more yeasts and

fewer lactobacilli. Eventually, the lactobacilli flora may change, with

more acid tolerant lactobacilli (e.g. L. pontis) prevailing. Such a

sourdough is found in the Vollmar and Meuser continuous sourdough

fermentation machines (there are 6 operating in Germany, and a diploma

candidate in our department characterised the microflora of several of

these: as the machine is operated with a 50% inoculum, the pH is never

above 4.1 - 4.3, and no L. sanfranciscensis is found in those doughs).

Yeasts are different: they donıt mind the pH at all, but are strongly

inhibited by acetic acid, and to a much lesser extend by lactic acid.

Increasing salt concentrations inhibit growth of lactobacilli, but yeasts

tolerate more salt. No salt is added to the sourdough until the final

bread dough, but the dough yield affects the salt concentration: with a

low dough yield (little water), the salt (ash) is dissolved in a smaller

water volume, and the salt concentration goes up: resulting in a slower

fermentation.

So much for the "in vitro³ theory. Surprisingly, Markus has found most of

the predictions to come true when he was looking at the cell counts at

different temperature, size of inoculum, salt concentration, and pH in rye

dough. The variation of the inoculum size was interesting: If he reduced

the inoculum size by 2, he had to wait almost exactly one generation time

(one doubling time of the lactobacilli) longer until the dough has reached

the same cell counts, pH, titrable acidity, and so on as the dough with

the higher inoculum. This was true for inoculum sizes between 1% and 20%:

at 50% inoculum, the pH is so low that the lactobacilli donıt really grow

well, and at an inoculum size of 0.1%, the pH and/or the oxygen pressure

in the dough are so high that the cells have a lag-time (see above) of an

hour. Thus, a scanty inoculum means one generation time longer

fermentation.

The generation time of L. sanfranciscensis in rye dough at 28°C is a

little less than an hour (figures may vary with different strains in

different flours, but itıs not much more or less than that), so if the

inoculation size is reduced from 20 to 2.5%, itıll take about three hours

more until the dough is ripe.

The question is, whether these findings are true for all flours and for

all organisms. The strain isolated by Kline and Sugihara does not differ

very much from the two strains Iıve been looking at. All the literature

available tells me that - as long as weıre looking at sourdoughs with a

tradition of continuous propagation - the system behaves the same way.

Differences may be between rye flour and white wheat flour: in white wheat

flour, the enzyme activities are so low that the organisms may run out of

food before the critical pH (lactobacilli) or the critical acetic acid

concentration (yeasts) is reached.

=============================================================

This discussion continues in the next post-- DCW

--

Dan Wing

Wagons@connriver.net

======================================================

PART 2 STARTS HERE

======================================================

From: wagons@connriver.net (Daniel Wing)

Subject: Long Technical Post 2

Date: 1998/05/25

Message-ID: <wagons-0301041021200001@port-1-26.wellsriver.connriver.net>

Organization: Cookeville Garage

Newsgroups: rec.food.sourdough

 

 

Rye is second to wheat as a bread grain

**

Comment No2: If discussing rye, it may be of importance, that rye quality

depends heavily on the weather conditions during the harvest: if is is

very humid before and during the harvest, sprouting starts, leading to

increased amylase activity. In a dry year, the amylase activities may be

rather low, so that the problem with the acidification is not very

prominent. It may also be noted that rye not only has a higher amylase

activity,a but also a higher protease activity, which is important for the

flavor development.

---------------------------------------------------------

In all, about 72 percent of the original kernel is left in most of the

white flour produced in the United States.

**

In Germany, the most common bread flour is wheat type 1050 (1.050 g ash

per kg) or rye type 1180. Many breads are "Vollkornbrot³. Type 550 (or 55)

is used only for white wheat bread, not a very big share in the market.

-----------------------------------------------------

Rye flour is commercially ground to a range of colors and particle sizes,

and the nomenclature is confusing.

**

If very coarsely groung flour is used, it should be swollen in water

before the dough mixing, Otherwise, it will take up water during dough

fermentation and proofing, and result in too stiff doughs. This is called

"Quellstueck³ by German bakers. As far as the enzyme activities go, see

comment No2 above. The difference in enzyme activities is also important

for the microorganisms: in rye flour they always have enough sugar

available due to the high enzyme activities, whereas in white wheat

flours, glucose (but not maltose) may be depleted during the fermentation.

----------------------------------------------------------------

Rye flour contains a great deal of amylase. Rye amylase resists

inactivation by heat to a greater extent than wheat amylase. It is so

resistant to inactivation that it is still active when the gelatinization

temperature of rye starch is reached in the oven

**

This is a very nice explanation. Also: see above (Comment No2)

----------------------------------------------------------

No laboratory test assesses taste, even though there are real differences

in the taste and texture of bread baked from otherwise similar flours.

**

This would be impossible, since the flour has no flavor whatsoever. Iıve

been preparing a research proposal recently with Markus Brandt and Prof.

Hammes in our lab, and Prof. Schieberle, probably the best expert in

flavor chemistry of bread, so Iıll go into some detail (and refer to it as

comment No3 later on). It may be useful to distinguish between taste and

aroma. Taste happens on the tongue, where only salty, bitter, sweet and

sour can be evaluated. Aroma is percieved in the nose: during chewing, the

volatile compounds diffuse to the receptors (mind that acetic acid, but

not lactic acid is volatile. Thus, the latter is just sour, while acetic

acid has aroma). There are about 15 compounds each (about 10 of them are

the same for wheat and rye bread, furthermore, crust and crumb have

different aroma volatiles) with which the impression of rye or wheat bread

is given (This is work of Prof. Schieberle in Munich).

To group the compounds according to their generation in dough, one may say

that:

i), they are produced by fatty acid oxidation by cereal enzymes upon dough

mixing (several baking aids contain soy flour with additional lipoxygenase

activity, and prolonged storage of whole flour leads to rancidity as

well). These compounds have a "green³, "bitter³ "tallowy³ or "metallic³

taste - not very pleasant. Lactic acid bacteria and yeasts do inactivate

these compounds in part, thus, fermentation reduced the "rancidity³ of the

bread.

ii) aroma compounds are produced by yeasts and lactobacilli. More of them

by yeasts, probably, though acetic acid also plays an important role.

These compounds often give a "flowery³, "yeasty³ or "malty³ flavor.

iii) The Maillard reaction is extremely important, especially for the

crust aroma compounds. However, the precursor chemicals for this type of

reactions are amino acids, and the levels of amino acids in flour is verym

low. In wheat, there is little, if any proteolytic activity (proteases

degrade protein to amino acids), so, whatever amino acids there are

produced by enzymes of lactic acid bacteria (there has been nice work done

on proteolysis in wheat dough by Dr. Marco Gobbetti at the University of

Perugia). In rye, the proteolytic activity of the flour is much higher,

but the proteases need acidification to a pH below 5 to have their optimum

activity (and, of course, a long fermentation time gives the enzymes more

time to work). Sourdough yeasts are consuming amino acids, meaning a

sourdough with a high yeast count has fewer amino acids than a dough

containing only lactobacilli. Addition of excess amounts of bakerıs yeast

(>4%) also leads to an increase of Maillard compounds, but that may not be

the aroma a sourdough baker is looking for. The most important flavor

compound in rye crust, methional, as well as in wheat crust,

2-acetyl-pyrroline, are Maillard products of the amino acids methionine

and ornithine, respectively.

As I mentionned, weıve been preparing a research proposal to figure out

which of the aroma compounds or aroma precursors (meaning chemicals

converted to aroma compounds during baking) are formed by which

microorganisms. In other words, other than acetic acid production, we

donıt know whether or not aroma is produced by yeasts and lactobacilli of

sourdough. There are a few good working hypotheses: Some, but not all

strains of L. sanfranciscensis convert arginine to ornithine (MOST

important flavor precursos in wheat), so this metabolic activity may be of

importance. Several other compounds are produced by yeasts (but we donıt

know whether the sourdough yeasts are more active than bakerıs yeast), and

all L. sanfranciscensis does convert the fatty acid oxidation products to

chemicals with less or no aroma intensity - but how this activity compares

to straight, bakerıs yeast dough, we donıt know.

============================================

continued in next post-- DCW

--

Dan Wing

Wagons@connriver.net

 

======================================================

PART 3 STARTS HERE

======================================================

 

 

From: wagons@connriver.net (Daniel Wing)

Subject: Long lTechnical post 3

Date: 1998/05/25

Message-ID: <wagons-0301041021590001@port-1-26.wellsriver.connriver.net>

Organization: Cookeville Garage

Newsgroups: rec.food.sourdough

 

 

 

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 donıt have starch degrading enzymes. A Spanish group has looked

for the development of maltodextrins during sourdough fermentation: as

lactobacilli and yeasts donıt 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.

----------------------------------------------------

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).

-----------------------------------------------------

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 inoculation³ is better than anything I was

writing to say the same thing. Cultured from the environment³ 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 inoculation³ youıll 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.³ 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 donıt 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)

--------------------------------------------------------

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 stages³ 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 weıve 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 "old³. Then, the definition of e.g. "three

stage sourdough processes³ 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 "modeling³ 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 processes³ does make no sense.

-----------------------------------------------------

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 bakerıs 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.

---------------------------------------------------------

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 youıve

rightfully pointed out, is certainly not the right criterium.)

----------------------------------------------------------

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 donıt 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).

-------------------------------------------------------------------

============================================

continued in next post-- DCW

--

Dan Wing

Wagons@connriver.net

 

 

======================================================

PART 4 STARTS HERE

======================================================

From: wagons@connriver.net (Daniel Wing)

Subject: Long Technical Post 4

Date: 1998/05/25

Message-ID: <wagons-0301041022540001@port-1-26.wellsriver.connriver.net>

Organization: Cookeville Garage

Newsgroups: rec.food.sourdough

 

 

 

Since many people new to natural leavens would like to bake San Francisco

sourdough, Desem bread, or German rye bread, let's look at some of their

characteristics, as determined by their leavens, ingredients, and

processes.

**

The microflora of German rye sour and Sanfrancisco sourdough is (almost)

identical. The difference is raw material and production process. Prof.

Hammes thinks that L. sanfranciscensis isolated from wheat or rye may have

different properties (e.g. degradation of arginine to ornithine, see

comment No3, or proteolytic activity (see comment No2: wheat has less

proteolytic activity by itself than rye). He still has to prove his point,

though.

-----------------------------------------------------------

That yeast is also resistant to a natural antibiotic made by the bacteria.

**

The most "antibiotic³ compound in sourdough is acetic acid. Although I

mentionned earlier that Candida milleri from Böcker Reinzucht Sauer (The

Saccharomyces exiguus described by Kline and Sugihara has been renamed to

Candida milleri as well) is more sensitive to acetic acid than the

lactobacilli, it certainly is much more resistant than bakerıs yeast.

Gobbetti says that L. sanfrancisco produces other organic acids that may

inhibit yeast growth, but I donıt know wheter or not the concentration in

the dough is high enough to make a difference. As far as I know, no other

antimicrobial compound in dough has been characterised.

-----------------------------------------------------------

Most German rye bread has at least 30 percent rye

**

I have the figures: 60% is "mixed rye bread³ containing both rye and

wheat, but more of the former. As far as the bread goes, rye only about as

important as wheat only. The situation is different for bagels, pretzels,

and so on. There is increasing interest in wheat sourdoughs: the 1 - 5%

addition of sourdough, which is sometimes replaced by a dried and "dead³

sourdough works, but not quite as well as it could. Which is why industry

is funding flavor research at the Universities of Hohenheim and Munich...

----------------------------------------------------------

Vollmar and Meuser showed that the rate of bacterial reproduction after

inoculation is self-regulated, within limits: if you add a small inoculum,

the bacteria will multiply faster than they will if it is larger, so the

static population (say 1,650 million cells/cc) is reached at the same time

in either case, about three and one-half hours.

**

The Vollmar and Meuser sourdough machine is not a very good example: as

pointed out in comment No1, it operates with an inoculum of 50%, which

makes the dough so acid from the beginning on the the lactobacilli donıt

like to grow fast. Between 1 and 20% inoculum, lactobacilli grow at the

same speed (giving rise to the dependency of fermentation time and

inoculum size explained earlier). The Vollmar and Meuser machine also has

a rather high yeast content (if youıve read their publication in Cereal

Chemistry; yeasts are above 100 million or more than 10% or the total cell

counts, while "normal³ starters such as the Sanfrancisco starter of the

Böcker Reinzucht Stater have only around 10 million or about 1% of the

total cell count.

--------------------------------------------------------

When cultures are fermented at higher temperatures, non-pathogenic

acid-tolerant contaminants such as Pediococcus (makes too much lactic

acid) and Acetobacter (makes to much acetic acid) can intrude and

dominate, affecting taste.

**

Pediococcus is probably less acid tolerant than L. sanfranciscensis, but

it grows at higher temperatures (as mentionned above, sanfranciscensis

does not like more than 35 - 37°C. Acetobacter is of no importance in

sourdoughs: it strictly requires oxygen for growth, and sourdough becomes

anaerobic (=without oxygen) very quickly due to the metabolism of yeasts

and lactobacilli. If youıve ever seen a vinegar fermenter you will notice

that several hundred liter of air are pumped through a liter of vinegar

during an hour: it is almost impossible to aerate sourdough in such a way.

--------------------------------------------------------------

Dr. Sugihara, who participated in the characterization of the flora of San

Francisco sourdough and several other cultures, was asked whether natural

sourdough cultures could be contaminated with commercial yeast. His reply

was no, not if you have a stable culture that is continuously maintained

with the same conditions and ingredients.

**

Dr. Sugihara is certainly right here. There was an experiment done by a

Dutch group: bakerıs yeast didnıt survive more than two refreshments. I

think that itıs the acetate that kills the yeast as its less acetate

tolerant than sourdough yeasts.

And to the margin note right next (CONCERNING THE ABILITY OF BACTERIAL

FERMENTATION TO RAISE A LOAF OF BREAD, WITHOUT YEAST): Weıve done the

experiments, it works quite well without yeast. The volume is somewhat

smaller, though. Markus Brandt has estimated the contribution of yeasts

and lactobacilli to gas production in a "normal³ sourdough: about 50%

comes from lactobacilli and yeasts each. The yeasts are fewer in numbers,

but larger in size.

--------------------------------------------------------

Bakers are interested in the acids produced by leaven microbes because

much of the distinctive flavor produced by leaven microbes comes in the

form of organic acids that are products of fermentation.

**

The production of lactic acid in dough in determined mainly by the

buffering capacity of the flour, i.e. the ash content. Dough yield and

temperature are much less important; as far as Spichers investigations go,

I think that the higher lactic acid concent of doughs with higher

temperatures or higher dough yields he measured is due mainly to the

faster fermentation at these conditions. (this holds true if you calculate

the lactate produced on the amount of flour in the dough: this ratio is

fairly constant). The amount of acetic acid produced is controlled mainly

on the availability of fructose. L. sanfranciscensis produced lactic acid

and ethano (and carbon dioxide) from maltose or glucose. If the organism

wants to produce the more oxidized end product, acetic acid, another

substrate must be reduced. L. sanfranciscensis reduced 2 moles of fructose

to mannitol per mole of acetic acid formed. The ratio of mannitol to

acetic acid in dough os about 1.8, fairly close to the theoretical value

of 2 if fructose was the only co-substrate that is reduced. During

fermentation, L. sanfrancisco starts to produce lactic acid and acetic

acid first, and forms lactic acid and ethanol only if the fructose is

depleted. There is a lot of fructose in dough, but not all of it is

available for the lactobacilli. Yeasts liberate some of the fructose bound

in glucofructans that thus becomes available for the lactobacilli (there

is some nice work that has been done by the Sugihara group, Saunders et

al., cereal chemistry, 1972 or 1973). If you to too high with the

temperature, you slow down yeast growth, and the acetic acid levels in the

dough decrease. For bakers, an easy way to increase the acetic acid

content is to add sugar 8that is sucrose,a consisting of glucose and

fructose). This wonıt increase the total titrable acidity, though, as that

is determined by the buffering capacity. Sugar addition (not too much, 1

or 2%) may speed up fermentation in white wheat flours: as mentionned

above, in contrast to whole wheat flour and rye flours, the enzyme

activities and thus the sugar concentrations are rather low and may limit

microbial metabolism.

As far as the influence of acetic acid and lactic acid on flavor go:

lactic acid has no influence on aroma, only on taste, while acetic acid is

an aroma volatile. So, I think it is not so much the ratio of lactic to

acetic acid, but more simply the acetic acid content that matters.

------------------------------------------------------------

Natural leavens should be actively fermenting and reproducing when they

are incorporated into a dough

**

Yeasts in dough donıt have to rely on oxygen for growth: if that were the

case, they woudnı t be there.

----------------------------------------------------------------------

The more accepted and consistently successful way to store a culture for a

month or so is to make a fresh and very stiff storage leaven, put it in a

well covered vessel ...

**

Such leavens may keep up to almost three month (my sister had a baby in

March and didnıt use her starter for almost three month. It was stored the

way you described here, and did come out well upon refreshment. The Böcker

Reinzuchtsauer is also distributed as stiff, refrigerated product. I think

the company does not guarantee storage stability of more than 4 weeks,

though.)

----------------------------------------------------------------------

Still there may be someone out there who does need to start a leaven

because of some terrible misfortune--

**

I think it does not matter when the first batch of a new sourdough stinks

- the good bacilli will come out eventually, and they may come faster if

fermentation is done around 25 - 30°C (as mentionned earlier, the

temperature optimum of L. sanfranciscensis is 32 - 33°C). There has been

nice work done in Rudi Vogels lab on the microflora of a freshly started

sourdough: first, there are Enterobacteria (Escherichia coli, Salmonella,

Enterobacter), highly undesirable organism that stink terribly, then there

are homofermentative lactobacilli (good, but no gas production), then

acid-tolerant, heterofermentative lactobacilli. I think, this took about

48 hours at 30°C. The stink at the beginning does not matter as the

organisms will be diluted out or die eventually. No L. sanfranciscensis,

though, these will occur only after repeated refreshments. Peter Stolz of

the Böcker company told me that it takes about two weeks of repeated

inoculations to get a good "sanfranciscensis³ sourdough. I donıt know

whether or not this process was sped up in his case as, due to his

workplace, his skin is all covered with L. sanfranciscensis.

-----------------------------------------------------------------

My biggest disagreement with her, though (NANCY SILVERTON), is about the

amount of material one should use in a starter.

**

I agree with you: one g of dough is one billion lactobacilli and 10

million yeasts: more than enough. In the lab, Iım doing most experiments

on a 1/10 ml scale, for dough refreshments at home, it does not get much

smaller than 10 g: itıs difficult to handle smaller amounts.

-------------------------------------------------------------

If leaven refreshment intervals are excessive

**

The main criterion of sourdoughs containing L. sanfranciscensis is the

repeated, frequent refreshment (not counted the storage in the

refrigerator). Peter Stolz said that one every 24 hours will suffice, if

intervals are much longer than that (lets say more than 3 days),

different, more acid tolerant organisms may evolve (e.g. L. pontis as

found in the Vollmar and Meuser Breasd maschines: these are refreshed

frequently, but with a very high inoculum).

---------------------------------------------------------------------

Refreshment schedules are always dependent on temperature.

**

See my earlier comment on the temperature dependency of growth of L.

sanfranciscensis and Candida milleri. Most of the typical sourdough yeasts

resemble C. milleri with respect to the temperature sensitivity (i.e. no

growth at 37°C).

-------------------------------------------------------------

Acidity can be expressed as flavor (an acid flavor), as pH, or as total

acidity.

**

That a good explanation of the total titrable acidity concept. (I find

students almost done with their degree still have difficulties with this

concept).

-------------------------------------------------------------------

At any given temperature the thinner starter will ferment faster and reach

a lower pH; but will not contain as much acid.

**

If you calculate the amount of acid produced on the weight of the flour

rather than the dough weight, the outcome -lactic acid per g flour -

should be pretty independent on dough consistency (not if very stiff

doughs are produced: the combined salt and acid stress leads to a

decreased acid production). Markus Brandt observed this in doughs (rye

flour, TA 180) if more than 2% salt were added.

-------------------------------------------------------------------

Together, caramels and Maillard products are responsible for much of the

flavor and aroma of fresh yeasted bread, although of these two, Maillard

products are moch more intensely aromatic.

**

This is right for both yeasted breads and sourdough breads, however, it is

important to note that whatever chemicals are reacting with each other

during baking must be formed during dough fermentation. (Schieberle in

Munich has done several nice studies: he supplied doughs with amino acids

and demonstrated that the levels of aroma compounds in the bread were

increased). So, formation of aroma precursors during dough fermentation is

crucial for the Maillard reaction.

==================

The end of this set of posts-- DCW

--

Dan Wing

Wagons@connriver.net