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Offline Pizza Napoletana

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2225 on: November 11, 2013, 08:50:30 AM »
Omid, can fermentation happen aerobically in yeast and bacteria? Why if yes or no? How do you define fermentation?

Dear Pulcinella, your questions fall within the realm of microbiology, and I am not a microbiologist to be able to competently answer your questions. Nonetheless, I will try my best.

Fermentation is a broad subject, and the metabolic diversity of bacteria and yeast can make this subject complex and perplexing. Because of the metabolic diversity of bacteria and yeast, there are many different types of fermentation, each utilizing a particularized fermentation pathway. Therefore, for the purpose of answering your questions as accurately as I can, I will limit this post to only sugar-fermenting bacteria and yeast (such as Saccharomyces cerevisiae, i.e., the baker’s yeast) that are commonly used in preparing pizza dough.

First, let me make some prefatory statements. Fermentation is a property of (but not limited to) fermentative microorganisms such as bacteria and yeast. Moreover, each species requires a particular type or particular types of substrates (i.e., saccharides or sugars) to metabolize. Which sugars are metabolized by different bacteria or yeast vary by species and strains within each species, although some may have the same substrate requirements. In understanding fermentation (and various fermentative microorganisms), it is imperative to understand:

1. What fermentable sugar or sugars (such as glucose, fructose, sucrose, maltose, pentose, etc.) the fermentative microorganisms use as sources of food;
2. What end products and byproducts the fermentable sugars are converted to in the course of fermentation by the microorganisms; and
3. The conditions (such as anaerobic, aerobic, etc.) under which the microorganisms ferment the sugars.

For the sake of brevity, I will limit this post to only one substrate, glucose (a six-carbon sugar), which is the most common fermentable sugar used by the bacteria and yeast that we are interested in. Basically, to make a long story short, the starch (i.e., amylose and amylopectin) molecules of wheat flour are enzymatically hydrolyzed in several stages to form glucose molecules before fermentation actually begins. 

In the science of physics, "energy" is defined as follows: "Energy is that property something has that enables it to do work." Cellular activity or cellular work in bacteria and yeast requires energy. No energy, no cellular work. Fermentation (in conjunction with glycolysis) is one mode of production of energy in bacteria and yeast so that they can carry out cellular activities in order to survive.

Bacteria and yeast have specialized energy- and matter-producing "metabolisms"—geared toward their biological survival. Fermentation is a metabolic function of fermentative bacteria and yeast. What is "metabolic function" or "metabolism"? Metabolism is the critical chains of biochemical reactions that occur within the lifespan of a living bacteria or yeast in order to sustain its biological life by producing energy and matter. To be more specific, metabolism is the cellular chemical reactions that extract energy from suitable nutrients (glucose) and convert the energy to usable forms in order to carry out catabolic (destructive) and anabolic (constructive) reactions:

1. Catabolic reactions are energy-producing reactions. Catabolism constitutes the chemical reactions that break down glucose molecules (besides the protein and lipid molecules of wheat flour) into smaller molecules in order to release and harvest the inherent potential energy of the chemical bonds (covalent bonds) of glucose. Anaerobic cellular respiration (fermentation) and aerobic cellular respiration are two examples of catabolic reactions.

2. Anabolic reactions are energy-demanding reactions. Anabolism constitutes the chemical reactions that synthesize larger molecules from smaller molecules. The synthesis of smaller molecules to form new molecules requires energy, which is sourced from catabolic reactions. Hence, catabolic reactions (such as aerobic respiration and fermentation) fuel anabolic reactions. Yeast cell reproduction, growth, and repair are few examples of anabolic reactions.

The interrelation between cellular catabolism and cellular anabolism indicates that aerobic respiration (which is an energy-producing catabolic reaction), anaerobic respiration (which is also an energy producing catabolic reaction, of which fermentation is a part), and yeast multiplication and growth (which are energy-demanding anabolic reactions) are interlinked.

Catabolic metabolism in yeast and many bacteria is of two types: aerobic cellular respiration (which requires oxygen as the terminal electron acceptor) and anaerobic cellular respiration (which requires an organic molecule, never oxygen, as the terminal electron acceptor). Aerobic and anaerobic respiration are comprised of several stages:

1) Stages of aerobic cellular respiration (where oxygen is required)
    a. Glycolysis (conversion of glucose to pyruvate)
    b. Pyruvate oxidation/carboxylation
    c. Citric acid cycle
    d. Electron transport chain & chemiosmosis

2) Stages of anaerobic cellular respiration (where oxygen is not required)
    a. Glycolysis (conversion of glucose to pyruvate)
    b. Fermentation
        1. Alcoholic fermentation (by yeast)
            a. Conversion of pyruvate to carbon dioxide and acetaldehyde
            b. Conversion of acetaldehyde to ethanol (alcohol)
        2. Lactic acid fermentation (by bacteria)
            a. Homolactic fermentation (conversion of pyruvate to lactic acid by homofermentative bacteria)
            b. Heterolactic fermentation (conversion of pyruvate to lactic acid, ethanol, and carbon dioxide by heterofermentative bacteria)
            c. Homo-Hetero-lactic fermentation (performed by facultative heterofermentative bacteria, which can switch between homo- & hetero-lactic fermentation)

So, you asked, "Can fermentation happen aerobically in yeast and bacteria?" According to my studies, NEVER. There is no such thing as "aerobic fermentation", although I have seen many websites and books that treat fermentation as a partly aerobic phenomenon. Here is an example. According to the website "Bake Info - Baking Industry Research Trust" of New Zealand (which is supposed to be a professional website):

Quote
Yeast uses sugars by breaking them down into carbon dioxide and water. The yeast needs lots of oxygen in order to complete this type of fermentation.

C6H12O6 + 6O2 ←→ 6CO2 + 6H2O+ Energy
   Sugar           yeast          Water

http://www.bakeinfo.co.nz/Facts/Bread-making/Bread-ingredients/Yeast


The yeast needs lots of oxygen in order to complete this type of fermentation?!! With all due respect, this is NOT fermentation, not at all. I know this as an indisputable fact. The cited equation is the overall chemical equation for "aerobic cellular respiration", not "anaerobic cellular respiration"—which is comprised of glycolysis (as the first stage) and fermentation (as the second stage). Please, take notice of the "O2" in the equation. Any professional microbiologist will tell you that the fermentation pathway is not equipped with the biochemical mechanisms to utilize oxygen in order to bring about oxidation (breakdown) of glucose (C6H12O6) to carbon dioxide (CO2) and water (H2O). Indeed, we need to be more critical in understanding the concept "fermentation", for it is often confused—by both professional and nonprofessional bakers—with almost the entire catabolic metabolism of bacteria and yeast.

The overall equation for alcoholic fermentation by yeast is:

C6H12O6 → Glycolysis (Pyruvate) → 2 C2H5OH + 2 CO2
 Glucose                                            Ethanol       Carbon Dioxide
©©©©©©                                     ©©+©©      ©+©

(Each "©" stands for one carbon atom.)

The overall equation for homolactic fermentation by homolactic bacteria is:

C6H12O6 → Glycolysis (Pyruvate) → 2 C3H6O3
 Glucose                                          Lactic Acid
©©©©©©                                  ©©©+©©©

The overall equation for heterolactic fermentation by heterolactic bacteria is:

C6H12O6 → Glycolysis (6-Phosphogluconate) → C3H6O3 + C2H5OH + CO2
 Glucose                                                        Lactic Acid   Ethanol    Carbon Dioxide
©©©©©©                                                      ©©©         ©©        ©

Fermentation is always anaerobic by nature. To say that fermentation can happen aerobically is not only illogical, but also a biological absurdity. The fermentation enzymes, in conjunction with their attendant cofactors and coenzymes, can only bring about oxidation of glucose molecules by "substrate-level phosphorylation", which is purely anaerobic. When bacteria or yeast shift from anaerobic to aerobic respiration, then they need to use "oxidative phosphorylation" (which is purely aerobic), in addition to  "substrate-level phosphorylation", in order to be able to cause oxidation of glucose to carbon dioxide, water, and energy in the forms of ATP and heat. 

Bear in mind that fermentation is carried out with or without the presence of oxygen. Nonetheless, fermentation is a purely anaerobic reaction. While it can take place in the presence of oxygen, oxygen is never involved in the reaction, nor does it alter the reaction or its outcome. The technical reason that fermentation can never be aerobic is that it, unlike aerobic respiration, lacks the biochemical mechanisms of citric acid cycle, electron transport chain, and chemiosmosis—where oxygen functions as the terminal electron acceptor.

As far as the bacterium and yeast cells are concerned, the ultimate goal of fermentation, in conjunction with glycolysis, is to generate biochemical energy (about 2 ATP net per glucose molecule) by oxidation of glucose—without the involvement of oxygen. And, As far as the bacterium and yeast cells are concerned, the ultimate goal of aerobic cellular respiration is to generate biochemical energy (about 36-38 ATP per glucose molecule) by oxidation of glucose—with the direct involvement of oxygen. Good day!
« Last Edit: November 11, 2013, 07:35:41 PM by Pizza Napoletana »
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Offline Serpentelli

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2226 on: November 11, 2013, 09:05:27 AM »
Omid,

As fascinated as I am by the knowledge and effort that goes into your posts here I am even more intrigued as to how you have come to have such a profound depth of knowledge about all of the biological systems that you describe so well!

You certainly would have been a huge help to me in the past when I was struggling with these same issues in school! Thanks for sharing your knowledge so freely and eloquently!

John K

PS: When making beer, I remember that the "wort" was formed when I boiled crushed malted barley in water. The main purpose for this (as far as I can remember) was to allow the heat of the water to break some of the starches (in the barley) down into shorter polysaccharide chains. This in turn made it easier for the yeast (added after the wort was cooled) to convert those polysaccharides into alcohol.

Is there any way (or reason) that this process could (or should) somehow be applied to the dough process? Obviously cooking flour in water would be a seemingly bad way to start making dough, but perhaps if only a portion of the total flour and water were prepared in this way (and added to the remaining flour and water after it was cooled) it would have an interesting effect on fermentation time, and dough consistency. I imagine that the glutenin and gliadin in the cooked portion of the flour would be denatured and rendered useless, but surely a small amount of vital wheat gluten could be added back in to overcome this......
« Last Edit: November 11, 2013, 09:17:55 AM by Serpentelli »
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Offline TXCraig1

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2227 on: November 11, 2013, 10:25:04 AM »
PS: When making beer, I remember that the "wort" was formed when I boiled crushed malted barley in water. The main purpose for this (as far as I can remember) was to allow the heat of the water to break some of the starches (in the barley) down into shorter polysaccharide chains. This in turn made it easier for the yeast (added after the wort was cooled) to convert those polysaccharides into alcohol.

Is there any way (or reason) that this process could (or should) somehow be applied to the dough process? Obviously cooking flour in water would be a seemingly bad way to start making dough, but perhaps if only a portion of the total flour and water were prepared in this way (and added to the remaining flour and water after it was cooled) it would have an interesting effect on fermentation time, and dough consistency. I imagine that the glutenin and gliadin in the cooked portion of the flour would be denatured and rendered useless, but surely a small amount of vital wheat gluten could be added back in to overcome this......

To what end? If you want more fermentable sugar, why not just add it directly to the dough? Why denature the gluten and gelatinize the starch in the process? Sounds like a recipe for dense, gummy crumb to me, but I'd be interested to hear the results if you give it a try.
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Offline TXCraig1

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2228 on: November 11, 2013, 10:30:55 AM »
It might sell well down here in the South though. I can see the advertising now: "Here at our pizzeria, we add gravy to the dough."  :-D
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Offline Serpentelli

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2229 on: November 11, 2013, 10:32:33 AM »
To what end? If you want more fermentable sugar, why not just add it directly to the dough? Why denature the gluten and gelatinize the starch in the process? Sounds like a recipe for dense, gummy crumb to me, but I'd be interested to hear the results if you give it a try.

I know, right?? It sounds like such a dumb idea that there'd be no reason whatsoever to try it. I guess its just the retired beermaker in me...

I'll let you know if it happens.

Totally agree with the "gravy inside" idea!! :-D

John K
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Offline TXCraig1

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2230 on: November 11, 2013, 11:17:05 AM »
The yeast needs lots of oxygen in order to complete this type of fermentation?!! With all due respect, this is NOT fermentation, not at all. I know this as an indisputable fact. The cited equation is the overall chemical equation for "aerobic cellular respiration", not "anaerobic cellular respiration"—which is comprised of glycolysis (as the first stage) and fermentation (as the second stage). Please, take notice of the "O2" in the equation. Any professional microbiologist will tell you that the fermentation pathway is not equipped with the biochemical mechanisms to utilize oxygen in order to bring about oxidation (breakdown) of glucose (C6H12O6) to carbon dioxide (CO2) and water (H2O). Indeed, we need to be more critical in understand the concept "fermentation", for it is often confused—by both professional and nonprofessional bakers—with almost the entire catabolic metabolism of bacteria and yeast.

In fact, facultative anaerobes such as yeast and some bacteria resort to fermentation precisely because there is no oxygen available. Aerobic reparation generates far more energy than fermentation and is always the favored metaboic pathway of facultative anaerobes when oxygen is available.  Fermentation is prevalent in dough because 1) there is very little oxygen in dough initially, and 2) the viscous nature of the substrate makes it all but impossible to transport a meaningful amount of oxygen from the exterior to the interior of the dough.
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scott123

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2231 on: November 11, 2013, 11:35:22 AM »
Do the baker and the biochemist have the same definitions for fermentation?  Hasn't the definition of fermentation, for the baker, come to include all the biochemical processes that occur between when a dough is made and when it's baked?  If you go by this meaning, "aerobic cellular respiration", since it's occurring (to some extent) in dough, a component of fermentation?

It was/is my understanding that aerobic respiration can play a significant role in poolishes- especially when a lot of air is incorporated via whisking.

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2232 on: November 11, 2013, 11:59:09 AM »
Do the baker and the biochemist have the same definitions for fermentation?  Hasn't the definition of fermentation, for the baker, come to include all the biochemical processes that occur between when a dough is made and when it's baked?  If you go by this meaning, "aerobic cellular respiration", since it's occurring (to some extent) in dough, a component of fermentation?

That may be the case, but the baker would be absolutely incorrect in his definition. Does it matter? A particular quote comes to mind: "If the pizza obsessives don't stand up and say "Stop calling that abomination NY style," if we don't take concrete steps to save pizza- to educate, the light will go out."

Quote
It was/is my understanding that aerobic respiration can play a significant role in poolishes- especially when a lot of air is incorporated via whisking.

I bet if you could ask the yeast, they would disagree that "a lot" of air is incorporated via whisking.
« Last Edit: November 11, 2013, 12:00:40 PM by TXCraig1 »
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scott123

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2233 on: November 11, 2013, 12:57:53 PM »
That may be the case, but the baker would be absolutely incorrect in his definition. Does it matter? A particular quote comes to mind: "If the pizza obsessives don't stand up and say "Stop calling that abomination NY style," if we don't take concrete steps to save pizza- to educate, the light will go out."

In your example, you're pointing towards an, imo, pretty clear perversion of meaning.   Two professions defining the same word differently isn't a perversion. New Yorkers own the right to define NY style pizza.  For the term fermentation, ownership is not that cut and dry. The baker's version is certainly a looser definition, but I don't necessarily see biochemists as having the sole defining rights.

Fermentation is already an umbrella term for numerous processes occurring in dough, and, because of this, isn't appropriate for discussing specifics anyway. If I'm discussing enzymes, it's 'enzyme activity,' not 'enzyme fermentation.'  In that sense, Omid's original point that the term 'aerobic fermentation' is confusing is perfectly sound, but if one is in a mixed company of bakers and biochemists, a phrase along the lines of 'aerobic yeast activity during fermentation' or 'aerobic respiration during fermentation' shouldn't be too terribly confusing for either  party.

I bet if you could ask the yeast, they would disagree that "a lot" of air is incorporated via whisking.

A lot of it boils down to the consistency of the poolish.  If the poolish is just the right consistency, you can beat a considerable amount of air into it with a whisk.  A long time ago, when I was doing quick ferments and was trying to be frugal with my yeast, I would boost yeast activity via this method. It's a very limited scope, but aerobic respiration, can, in certain settings, play a role in the manner in which a dough ferments.


Mal

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2234 on: November 11, 2013, 01:20:22 PM »
re: pregelatinized starch
I've played around with adding a cooked flour and water mixture (i.e. wallpaper paste :-D) to dough to see what effects there were on fermentation time. The results were disappointing both in terms of fermentation (v. little difference) and the negative effects on gluten/dough strength. As I understand it, the starch recrystallises as the mixture cools down anyway.

I've read that some asian bakeries add this mixture (called ?water roux? I think?) to their bread doughs with the aim of making the final products softer but I highly doubt it's appropriate for pizza dough.

« Last Edit: November 11, 2013, 01:31:54 PM by Mal »

Offline arspistorica

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2235 on: November 11, 2013, 01:48:41 PM »
Fermentation is a broad subject, and the metabolic diversity of bacteria and yeast can make this subject complex and perplexing. Because of the metabolic diversity of bacteria and yeast, there are many different types of fermentation, each utilizing a particularized fermentation pathway. Therefore, for the purpose of answering your questions as accurately as I can, I will limit this post to only sugar-fermenting bacteria and yeast (such as Saccharomyces cerevisiae, i.e., the baker’s yeast) that are commonly used in preparing pizza dough.

Indeed, we need to be more critical in understand the concept "fermentation", for it is often confused—by both professional and nonprofessional bakers—with almost the entire catabolic metabolism of bacteria and yeast.

To narrowly define fermentation in the strict biochemical sense (i.e., as a specific metabolic event or events performed in the absence of the electron transport chain) is but one way to look at things.  Should bakers and pizzamakers henceforth refer to their craft as "fermentation in addition to (or as well as) the 'entire catabolic metabolism' of the involved microbiota?"  Because aren't we, as bakers and as pizzamakers, concerned with more than just the metabolic outcomes of ethanol, carbon dioxide, lactate and acetate?
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Mal

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2236 on: November 11, 2013, 01:55:53 PM »
To narrowly define fermentation in the strict biochemical sense (i.e., as a specific metabolic event or events performed in the absence of the electron transport chain) is but one way to look at things.  Should bakers and pizzamakers henceforth refer to their craft as "fermentation in addition to (or as well as) the 'entire catabolic metabolism' of the involved microbiota?"  Because aren't we, as bakers and as pizzamakers, concerned with more than just the metabolic outcomes of ethanol, carbon dioxide, lactate and acetate?

Hear hear.  Fermentation is a very broad subject and necessarily so.  Soy sauce is considered to be "fermented" where proteolysis is the key process and so similar processes in bread making and pizza making should receive equal recognition for their role in forming flavor precursors.

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2237 on: November 11, 2013, 01:58:51 PM »
In your example, you're pointing towards an, imo, pretty clear perversion of meaning.   Two professions defining the same word differently isn't a perversion. New Yorkers own the right to define NY style pizza.  For the term fermentation, ownership is not that cut and dry. The baker's version is certainly a looser definition, but I don't necessarily see biochemists as having the sole defining rights.

Fermentation is already an umbrella term for numerous processes occurring in dough, and, because of this, isn't appropriate for discussing specifics anyway. If I'm discussing enzymes, it's 'enzyme activity,' not 'enzyme fermentation.'  In that sense, Omid's original point that the term 'aerobic fermentation' is confusing is perfectly sound, but if one is in a mixed company of bakers and biochemists, a phrase along the lines of 'aerobic yeast activity during fermentation' or 'aerobic respiration during fermentation' shouldn't be too terribly confusing for either  party.

This is not about perversion; it’s about precision. In the sense of understanding and improving baking through the application of science as Omid has done here, one cannot use "fermentation" in the loose sense that perhaps some bakers might.

I would also add that using a word to mean something is not the same as it being defined to mean that something. There is no accepted definition of fermentation for baking use as there is for science. As such, the word is largely meaningless when used in any sense other than the scientific. This is where I was going (apparently clumsily) with the quote – just because someone calls something by a particular name, doesn’t make it so.
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Offline TXCraig1

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2238 on: November 11, 2013, 02:03:15 PM »
Hear hear.  Fermentation is a very broad subject and necessarily so.  Soy sauce is considered to be "fermented" where proteolysis is the key process and so similar processes in bread making and pizza making should receive equal recognition for their role in forming flavor precursors.

Because it's a broad subject we should broaden it further to include things that it does not include? What sense does that make?

(It may be time for a split subject)
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scott123

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2239 on: November 11, 2013, 02:05:43 PM »
Okay, so, if 'fermentation' doesn't incorporate all the biochemical processes in dough, what's the term that does?  Precision or not, you can't just take away a term used by just about every baker and not have a suitable replacement. And, no, I don't think 'proofing' is it, especially since some people equate 'proof' with a single rise of the dough.

You give me a suitable alternative term for the whole shebang, I'll use it.

Offline arspistorica

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2240 on: November 11, 2013, 02:34:41 PM »
Okay, so, if 'fermentation' doesn't incorporate all the biochemical processes in dough, what's the term that does?  Precision or not, you can't just take away a term used by just about every baker and not have a suitable replacement. And, no, I don't think 'proofing' is it, especially since some people equate 'proof' with a single rise of the dough.

You give me a suitable alternative term for the whole shebang, I'll use it.

"Fermentation," as an historical term and before 1837, was applied in a general sense, as it is today.  In fact, most of the world's leading researchers on this subject (the microbiology of sourdough; the biochemistry of cereal sciences) use the term in this very way; otherwise, life would become very tedious.  It should go without saying one word can have two or more meanings.
« Last Edit: November 11, 2013, 02:38:19 PM by arspistorica »
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Offline TXCraig1

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2241 on: November 11, 2013, 06:09:34 PM »
Okay, so, if 'fermentation' doesn't incorporate all the biochemical processes in dough, what's the term that does?  Precision or not, you can't just take away a term used by just about every baker and not have a suitable replacement. And, no, I don't think 'proofing' is it, especially since some people equate 'proof' with a single rise of the dough.

You give me a suitable alternative term for the whole shebang, I'll use it.

I'm not trying to take anything away from anyone's baking lexicon. I call it fermentation too, and functionally speaking that's what it is as there simply isn't enough oxygen in dough to worry about aerobic processes.



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scott123

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2242 on: November 11, 2013, 08:09:02 PM »
I'm not trying to take anything away from anyone's baking lexicon. I call it fermentation too, and functionally speaking that's what it is as there simply isn't enough oxygen in dough to worry about aerobic processes.

Anecdotally, as I mentioned, I've seen the results in whisked poolish. Also, it's most likely insignificant, but I think it might be a factor with the air introduced with stretch & folds. John Fazzari seems to have made inroads in proving that stretch & folds introduce oven spring benefits that traditional kneading fails to provide.  It's probably just the introduction of actual pockets of air rather than the air's aerobic impact on yeast, but, at this point, I wouldn't rule anything out.

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2243 on: November 11, 2013, 10:11:59 PM »
Anecdotally, as I mentioned, I've seen the results in whisked poolish.

What did the results look like?
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Offline Pulcinella

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2244 on: November 12, 2013, 01:31:31 AM »
Omid, thank you for your detailed response. Apparently fermentation is lot more complex than I thought. Where does fermentation by natural sourdough starter fit in this scheme, if you don't mind? Thnk you

Offline arspistorica

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2245 on: November 12, 2013, 07:08:39 AM »
I'm not trying to take anything away from anyone's baking lexicon. I call it fermentation too, and functionally speaking that's what it is as there simply isn't enough oxygen in dough to worry about aerobic processes.

Just because oxygen is not used as the terminal electron acceptor in starch-based lactobacilli and yeast fermentations does not mean oxygen has no impact on the kinetics of fermentation.  Quite the opposite is true, profoundly so.  E.g., in the increased presence of oxygen the gene expression of Lb sanfranciscensis shows an over-expression of NADH oxidases in its genome, as well as gshR (gluthathione reductase) and/or other thiol-activated systems.  This has significant metabolic consequences downstream:  aeration (through stirring or even stretching and folding) generates the highest amount of acetate possible in most heterofacultative lactobacilli under equal conditions, say, in the presence of the other electron acceptors responsible for producing acetate (fructose, citrate, malate or pyruvate).  Oxygen invokes a stress response that can increase cell size, density and growth rate; induces greater barotolerance (and hence cold tolerance) by over-expressing proteins required for thickening the cell wall; changes dough rheology through interaction with thiol compounds; etc.

The above reasons are why Italian sourdough bakers (who are generally no lovers of acetic acid) go to such great lengths to limit their culture's exposure to oxygen (this is in addition to using lower-extraction flours and hydration rates; increasing the frequency of feeds and fermentation temperatures; and often adding salt to their starters).
« Last Edit: November 12, 2013, 07:25:33 AM by arspistorica »
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Offline Pizza Napoletana

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2246 on: November 12, 2013, 08:56:34 AM »
Omid, thank you for your detailed response. Apparently fermentation is lot more complex than I thought. Where does fermentation by natural sourdough starter fit in this scheme, if you don't mind? Thnk you

You asked, "Where does fermentation by natural sourdough starter fit in this scheme?" I do not know, but I can make some conjectures. If I understand your concern properly, this is one area that I usually struggle with. So, I do not know how reliable my answer is going to be. For me, the fermentative properties of sourdough cultures are usually more difficult to pin down and comprehend than the fermentative properties of Saccharomyces cerevisiae (the baker’s yeast). From my perspective, when I use baker’s yeast, I already know the microorganism that I am dealing with (namely, S. cerevisiae). In addition, I know its general behavior and metabolic requirements. On the other hand, when I use a sourdough culture, I do not know, with specificity, the fermentative agents that I am dealing with. Moreover, if it is a new culture, it takes me some time to observe and comprehend the culture’s general behavior under various circumstances.

If I am not mistaken, baker’s yeast is capable of only one type of fermentation, namely, the alcoholic or ethanol fermentation, which is basically a three-step process:

1) Glycolysis (conversation of glucose to pyruvate),
2) Decarboxylation (conversion of pyruvate to carbon dioxide and acetaldehyde via enzyme pyruvate decarboxylase),
3) Dehydrogenation (conversion of acetaldehyde to ethanol via enzyme alcohol dehydrogenase.)   

Generally, when you utilize any form of baker’s yeast (dry yeast, cake/fresh yeast, liquid yeast), you are basically using one type of fermentative microorganism to inoculate your dough with. On the other hand, when you employ a sourdough culture as your inoculum, you are using more than one fermentative microorganism—in some cases as many as eighteen (18) different microorganisms. And, keep in mind that the types of sugars required by different microorganisms vary by species and strains within species, although some may have the same sugar requirements. (To the best of my knowledge, bacteria and yeast can only catalyze the sugars that their DNAs code for. For instance, while baker’s yeast can ferment glucose, they are unable to ferment lactose, simply because the yeast lack the proper enzyme, lactase, to break down the lactose molecules. Enzymes are proteins and are coded for by genes. The baker’s yeast does not have the genes that code for lactase enzyme.)

Therefore, in understanding the fermentative properties of sourdough cultures, you are most likely dealing with:

1) Various types of glycolysis:
    a. Embden-Meyerhof pathway (the classic glycolysis, used by yeasts and many bacteria)
    b. Pentose phosphate pathway aka pentose phosphoketolase pathway (used by heterolactic acid bacteria)
    c. Entner-Doudoroff pathway (used by some bacteria)

2) Various types of fermentation:
    a. Alcoholic fermentation (used by yeast and at least one known bacteria, producing ethanol and carbon dioxide)
    b. Lactic Acid fermentation
        1. Homolactic fermentation (used by homolactic bacteria, producing lactic acid and no carbon dioxide)
        2. Heterolactic fermentation (used by heterofermentative bacteria, producing lactic acid, ethanol, and carbon dioxide)
        3. Homo-hetero-lactic fermentation (used by facultative heterolactic bacteria, able to switch between homo- & hetero-lactic fermentation)

In comparison, in understanding the fermentative properties of S. cerevisiae, you are essentially dealing with:

1) Embden-Meyerhof pathway (the classic glycolysis), and
2) Alcoholic fermentation (products of which are ethanol and carbon dioxide)

These primordial microbes, the bacteria, as opposed to yeasts, show a great deal of diversity in their metabolisms and fermentative capabilities, making us non-specialists really toil at understanding them.

It is said that one distinctive feature of sourdough microorganisms is their ability to symbiotically (non-competitively) ferment sugars. In principle, a sourdough culture is said to be composed of two types of microorganisms: lactic acid bacteria (for example, a species of Lactobacillus) and wild yeast (for example, a suitable species of Candida). Both microorganisms symbiotically metabolize the sugars in dough. For instance, while the bacteria concentrate on metabolizing certain types of saccharides, the wild yeast focus on digesting certain other types of saccharides—without competing with the bacteria over the resources. The bacteria ferment specific sugars to lactic acid if they are homolactic fermenters; the bacteria ferment specific sugars to lactic acid, ethanol, and carbon dioxide if they are heterolactic fermenters; and/or the bacteria switch between homolactic and heterolactic fermentation if they are facultative heterofermentative bacteria. Meanwhile, the wild yeast, akin to S. cerevisiae, ferment their prescribed sugars to ethanol and carbon dioxide.

As an example, let us briefly take a look at the well-known San Francisco sourdough culture. Basically, the culture is reported to contain two principal types of microorganisms: (1) heterolactic acid bacteria known as Lactobacillus sanfranciscensis and (2) wild yeast known as Candida humilis. Generally, the bacteria-yeast ratio is reported to be about 100:1. The bacteria normally outnumber the yeast cells, as it is the case with other sourdough cultures. L. sanfranciscensis, which are obligate heterofermentative bacteria, require maltose (a di-saccharide composed of two glucose molecules) and glucose as the principal fermentable sugars. While the wild yeast are unable to metabolize maltose, they are able to metabolize glucose. The bacteria ferment the sugars via the pentose phosphate pathway (or the heterofermentative pathway), producing lactic acid, ethanol, and carbon dioxide. On the other hand, the yeast ferment the sugars via the Embden-Meyerhof pathway and alcoholic fermentation, producing ethanol and carbon dioxide. The sugar requirements of the bacteria and yeast and their use of different fermentative pathways do not promote them to compete over the resources, but create conditions under which they can coexist symbiotically. The bacteria cleave one maltose molecule into two molecules: glucose and glucose-1-phosphate. Next, the glucose is released into the dough and the glucose-1-phosphate is reduced to glucose-6-phosphate, which then goes through the pathway of heterofermentation to produce lactic acid, ethanol, and carbon dioxide. Meanwhile, the glucose molecules released into the dough can be ingested by the yeast in order to be fermented into ethanol and carbon dioxide. This is a very rough description and by no means accurate. In addition, it does not account for formation of acetic acid.

If anyone has a description or model of symbiotic fermentation by sourdough microflora, please share. Good day!

Omid
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Offline arspistorica

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2247 on: November 12, 2013, 09:58:26 AM »
If anyone has a description or model of symbiotic fermentation by sourdough microflora, please share. Good day!

Symbiosis (or non-competitive life requirements) in sourdough cultures is merely an outcome of whichever organisms are the fittest for a particular sourdough matrix at the time, and is by no means descriptive of sourdough microbiota in general.  There are as many stable relationships borne of antagonistic relationships as there are of synergistic, and these two elements will always be in flux, due quite obviously to the ability for "successful" (dominant) organisms to evolve to their external conditions.  These stable relationships come from these organisms wanting similar living conditions, just like roommates (e.g., in temperature and pH, the two most important process parameters for determining the make-up of a culture outside of substrate specificity), as well as having evolved similar stress responses to the harsh realities of living in a starch and water mixture.

Stability in a particular sourdough's microbiotic consortia is an afterthought; it only occurs after a baker repeats the same conditions over and over, selecting for whichever strains are the most suitable.  There's much, much more to this topic than just preferred carbon source (amino acid catabolism, e.g.).

Science understands very little about these matters but makes slow progress every day.  Even this past year researchers have uncovered species (both yeast and lactobacilli) never seen in sourdoughs before, some of which were entirely unknown before being discovered, and some of which utilise metabolic pathways never seen before.

The uniformity in species recovered from sourdoughs has more to do with human involvement than anything else, through our agricultural methods, dietary preferences, health-care technology, and so on.  I have long maintained Lb SF is and has been the dominant organism in sourdough much, much longer than researchers suspect (in the tens of thousands of years, beginning in Africa), and there's a team out of the Netherlands that will be publishing research pointing in this direction later this year.  Sourdough species should be seen as highly domesticated (selected for), similar to any other livestock that factor into our diets or living conditions.

Speaking of which, time for me to go divide a dough made up of one of these "wild" microbiotic cultures!
« Last Edit: November 12, 2013, 11:33:48 AM by arspistorica »
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scott123

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2248 on: November 12, 2013, 11:06:49 AM »
What did the results look like?

The yeast was considerably more active with whisking than without.

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Re: A PHILOSOPHY OF PIZZA NAPOLETANISMO!
« Reply #2249 on: November 18, 2013, 05:37:09 AM »
In light of the brief discussions we had in regard to aerobic and anaerobic reactions, I would like to share with you the pictures attached hereunder. Yesterday, using a double diving arms mixer by Pietroberto (which has an amazing ability to aerate dough), we made about 45 kilos of dough at Pizzeria Bruno. The dough was mixed for about 20 minutes without interruptions. When I turned off the mixer, the dough immediately began to settle down, whereupon I distinctly heard some of the trapped air in the dough to forcibly gush out, akin to a punctured tire rapidly deflating. This occurrence is not unusual; it happens often, both during and after mixing. Next, with the aid of a knife, I carefully cut a big chunck of the dough to take a look inside the dough mass.

The first and second pictures, below, show what I saw. Notice all the air pockets trapped inside the dough. There were multitudes of tiny air pockets that are not visible in the pictures. My Kitchen Aid and Santos mixer can not aerate dough this well.

I am not trying to imply that the dough was aptly oxygenated to promote aerobic cellular respiration in the yeast cells in the dough. I do not know if that was or was not the case, but it would be interesting to know the impact of the air bubbles, if any at all, on the metabolic activities of the yeast cells. Perhaps, as Craig stated, the viscosity of the dough makes it difficult for the oxygen to significantly penetrate and diffuse throughout the dough system.

As far as I know, oxygen (which constitutes about 20% of the air around us) need to be made available to the yeast cells. The cells, at least S. cerevisiae, can not proactively seek oxygen because they are not motile (capable of self-motion). Therefore, it seems to me that they need to go with the flow in the dough. Hence, the fluid mechanics of dough seems to be another consequential factor to reckon with. Last, I make the assumption that the water, used in making dough, holds a certain amount of dissolved oxygen, depending on the water temperature and other factors.

By the way, I have noticed that the air pockets usually disappear shortly after I take the dough out of the mixer bowl and place it on the countertop. I do not know how much of them escape into the environment and how much of them dissipate in the dough. Good day!

Omid
« Last Edit: November 19, 2013, 06:28:54 PM by Pizza Napoletana »
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