Sources for learning about fermentation?

[helgibelgi]

Hi everyone

Do you know of a good place online where I can find information about the science of fermentation?

I tried searching the forum a bit, but the search function is really not that great.

I'm writing an article about fermentation and the goal is to describe everything that goes on in layman's terms, but with all the relevant chemistry and further reading for those who are interested. Therefore I'm looking for free information that anyone can use. It's going to be a very detailed article that leaves (hopefully) nothing out. It's for a website.

Thanks

 

[botigol]

This looks like a good place to start:

https://www.homebrewtalk.com/showthread.php?t=107287

 

[ajdelange]

Get any good biochemistry text. There will be a chapter on fermentation.

Look up 'Glycolysis' on Wikepedia.

When you get to:

Pyruvate + NADH + H+ → Lactate + NAD+

which describes what happens in humans, substitute

Pyruvate ---> CO2 + acetaldehyde

and

acetaldehyde + NADH + H+ → Ethanol + NAD+

CH3CHO + NADH + H+ → CH3CH2OH + NAD+

That's the science of fermentation. Fermentation science is another matter being a course of study leading to careers in brewing, distilling, oenology etc.

 

[helgibelgi]

This looks like a good place to start:

https://www.homebrewtalk.com/showthread.php?t=107287

Thanks, I did see that thread. I Like the University of Arizona links. This will be helpful to understand some fundamental things. But I'm looking for detailed information about fermentation specifically.

 

[helgibelgi]

Get any good biochemistry text. There will be a chapter on fermentation.

Look up 'Glycolysis' on Wikepedia.

When you get to:

Pyruvate + NADH + H+ → Lactate + NAD+

which describes what happens in humans, substitute

Pyruvate ---> CO2 + acetaldehyde

and

acetaldehyde + NADH + H+ → Ethanol + NAD+

CH3CHO + NADH + H+ → CH3CH2OH + NAD+

That's the science of fermentation. Fermentation science is another matter being a course of study leading to careers in brewing, distilling, oenology etc.

Thanks. I already have pretty good information about glycolysis, the krebs cycle and ethanol production in yeast. But the problem is that it focuses only on glucose, pyruvate, acetaldehyde and ethanol. I haven't been able to find any good information about processes or pathways that make use of nutrients, or even why exactly oxygen is needed for the krebs cycle, or about the creation of flavour compounds (off flavor or good).

I'm looking for very detailed information that explains the chemistry or least references the related chemistry.

 

[orangehero]

Brewing Yeast Fermentation Performance

Brewing Yeast and Fermentation

And of course:

Yeast: The Practical Guide to Beer Fermentation (Brewing Elements)

The latter is already broken down to layman's terms. I don't know what your background is, but there are plenty of sources already in layman's terms. Your comment about not knowing the role of oxygen in the Kreb's cycle suggests your biology background is limited. The yeast metabolism we are intersted in is anaerobic.

For our beer brewing use let's say fermentation is the anaerobic process that involves the conversion of sugars to ethanol and carbon dioxide. That in itself is a very complex topic. The creation of flavor compounds is a separate and even more complex one.

Learning the science of fermentation is not a light task.

 

[ajdelange]

Thanks. I already have pretty good information about glycolysis, the krebs cycle and ethanol production in yeast.
But the problem is that it focuses only on glucose, pyruvate, acetaldehyde and ethanol.

Understand EMP and you should be able to understand any other pathway such as the fructose phosphate pathway which flows into EMP a few steps in. Most of fermentation depends on EMP once 'inversion' of maltose into two glucoses has taken place.

I haven't been able to find any good information about processes or pathways that make use of nutrients,

If you understand the pathways you will see where the 'nutrients' come into the picture. Obviously if Mg++ is needed as a cofactor for an enzyme it is clear that Mg++ is needed for fermentation. If you look at the nucleotides upon which fermentation so highly depends you will see they contain lots of nitrogen and so obviously nitrogen is needed for them but even more is needed for synthesis of proteins so you need to check out how yeast do that.

... or even why exactly oxygen is needed for the krebs cycle,

It isn't. That comes in further down the respiratory pathway (oxidative phosphrylation) which pathway is not used because yeast do not respire while they are fermenting. If you don't understand that then you have a long way to go and should start with a good biochem text as I recommended in my previous post. It is very unlikely that you will be able to provide reliable information in laymans' terms if you do not have a good understanding of the processes your self.

or about the creation of flavour compounds (off flavor or good).

Fermentation does not produce flavor compounds. They are produced via other pathways. Diacetyl, for example, comes from leakage from the valine synthesis pathway so you must research and understand that. There are plenty of sources for this information. You will need to find them but won't even know of their existence until you understand the overall biochemistry of beer, not just fermentation. A good brewing text, or actually several as some are good in some areas and abysmal in others while a different text might be complelentary.

I'm looking for very detailed information that explains the chemistry or least references the related chemistry.

You are asking a question that is somewhat like: "What's a good reference that explains in detail the influence of the Roman Catholic church on western civilization". There ain't no such animal. It seems, at this point, that you are trying to bite off a great deal more than you are able to chew. It's going to take a big investment of your time to get to where you want to be. It's a worthwhile investment, IMO, because the more you understand the underlying science the better your chances of producing good beer.

 

[helgibelgi]

Brewing Yeast Fermentation Performance

Brewing Yeast and Fermentation

And of course:

Yeast: The Practical Guide to Beer Fermentation (Brewing Elements)

The latter is already broken down to layman's terms. I don't know what your background is, but there are plenty of sources already in layman's terms. Your comment about not knowing the role of oxygen in the Kreb's cycle suggests your biology background is limited. The yeast metabolism we are intersted in is anaerobic.

For our beer brewing use let's say fermentation is the anaerobic process that involves the conversion of sugars to ethanol and carbon dioxide. That in itself is a very complex topic. The creation of flavor compounds is a separate and even more complex one.

Learning the science of fermentation is not a light task.

Thank you so much for the book suggestions! You're right, my biology background is very limited. But I trust myself to be able to learn anything, as long as my interest drives me forward. I took a course on beer chemistry online at the university of oklahoma recently and found out that even though I have been brewing for almost 5 years I still don't understand the fundamental chemistry deeply enough.

 

[helgibelgi]

Understand EMP and you should be able to understand any other pathway such as the fructose phosphate pathway which flows into EMP a few steps in. Most of fermentation depends on EMP once 'inversion' of maltose into two glucoses has taken place.

If you understand the pathways you will see where the 'nutrients' come into the picture. Obviously if Mg++ is needed as a cofactor for an enzyme it is clear that Mg++ is needed for fermentation. If you look at the nucleotides upon which fermentation so highly depends you will see they contain lots of nitrogen and so obviously nitrogen is needed for them but even more is needed for synthesis of proteins so you need to check out how yeast do that.

Lets see if you can help me confirm what I'm thinking right now. So if a pathway calls for an enzyme, for example hexokinase for the phosphorylation of glucose, then is it correct to say that the yeast needs: protein to make the hexokinase enzyme in the first place, Mg and ATP (and therefore phosphate) to be able to make use of hexokinase in the phosphorylation of glucose?

And if I understand this correctly, I could use the same logic for all the other pathways/reactions that occur. And by going through everything I should be able to derive all/most of the 'nutrient' requirements for a healthy fermentation.

Quote:
Originally Posted by helgibelgi View Post
... or even why exactly oxygen is needed for the krebs cycle,
It isn't. That comes in further down the respiratory pathway (oxidative phosphrylation) which pathway is not used because yeast do not respire while they are fermenting. If you don't understand that then you have a long way to go and should start with a good biochem text as I recommended in my previous post. It is very unlikely that you will be able to provide reliable information in laymans' terms if you do not have a good understanding of the processes your self.

You're right of course that the krebs cycle isn't really a part of fermentation in a strict sense. But I want to explain in the article what happens to the oxygen in the wort and why you would want oxygen in your wort.

After reading about the krebs cycle I wasn't really sure about where oxygen was needed. But after a second look at it, I'm guessing that it is needed to oxidize the pyruvate (that was made during glycolysis) and I'm guessing it needs to be oxidized to be able to combine it with Acetyl-CoA. Is this correct?

Quote:
Originally Posted by helgibelgi View Post
... or about the creation of flavour compounds (off flavor or good).
Fermentation does not produce flavor compounds. They are produced via other pathways. Diacetyl, for example, comes from leakage from the valine synthesis pathway so you must research and understand that. There are plenty of sources for this information. You will need to find them but won't even know of their existence until you understand the overall biochemistry of beer, not just fermentation. A good brewing text, or actually several as some are good in some areas and abysmal in others while a different text might be complelentary.

This is what I consider to be most valuable information for brewers. To understand why and how flavor compounds are created. It seems to me that most brewers are satisfied with a simple method of trial and error regarding this topic without any underlying understanding of what's really going on (and I'm one of these brewers, but hopefully not for too much longer). Of course everything else that we talked about is also important, but more as a foundation. I guess I can write a whole new article only about this topic (It looks like I'll have to).

Thanks again for your answers! They are always so helpful!

 

[ArcLight]

>>You're right of course that the krebs cycle isn't really a part of fermentation in a strict sense. But I want to explain in the article what happens to the oxygen in the wort and why you would want oxygen in your wort.

Oxygen in wort is not really used for respiration, it's used for Sterol production, to strengthen the plasma membrane. There is something called the Crabtree effect where above a low threshold of sugar concentration, the yeast will ferment, even in the presence of Oxygen.

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Contin/overload.html

 

[ajdelange]

Lets see if you can help me confirm what I'm thinking right now. So if a pathway calls for an enzyme, for example hexokinase for the phosphorylation of glucose, then is it correct to say that the yeast needs: protein to make the hexokinase enzyme in the first place, Mg and ATP (and therefore phosphate) to be able to make use of hexokinase in the phosphorylation of glucose?

Definitely on the right track here though rather than say that protein is required you might want to say that nitrogen and amino acids which contain nitrogen (though they come from proteolysis of the malt) are needed. The yeast will then synthesize the amino acids (and proteins and nucleotides) from the available nitrogen. Most commercial yeast 'nutrients' contain a large proportion of urea and diammonium phosphate the latter of which provides both the the nitrogen and phosphorous for ATP, ADP, NAD etc.

And if I understand this correctly, I could use the same logic for all the other pathways/reactions that occur. And by going through everything I should be able to derive all/most of the 'nutrient' requirements for a healthy fermentation.

Yes, I think so.

You're right of course that the krebs cycle isn't really a part of fermentation in a strict sense. But I want to explain in the article what happens to the oxygen in the wort and why you would want oxygen in your wort.

As was pointed out in #10 it goes to sterol formation.

After reading about the krebs cycle I wasn't really sure about where oxygen was needed. But after a second look at it, I'm guessing that it is needed to oxidize the pyruvate (that was made during glycolysis) and I'm guessing it needs to be oxidized to be able to combine it with Acetyl-CoA. Is this correct?

The pyruvate is non oxidatively decarboxylated:

CH3COCOOH --> CH3CHO + CO2

giving acetaldehyde which is then reduced to ethanol by NADH.

 

[helgibelgi]

>>You're right of course that the krebs cycle isn't really a part of fermentation in a strict sense. But I want to explain in the article what happens to the oxygen in the wort and why you would want oxygen in your wort.

Oxygen in wort is not really used for respiration, it's used for Sterol production, to strengthen the plasma membrane. There is something called the Crabtree effect where above a low threshold of sugar concentration, the yeast will ferment, even in the presence of Oxygen.

http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Contin/overload.html

Thanks, this clears up one misunderstanding that I have apparently been having about the use of oxygen.

It's very confusing when I read that under aerobic conditions pyruvate is used in the krebs cycle and under anaerobic conditions pyruvate is converted to acetaldehyde and then into ethanol.

so if I got this right, it looks like the yeast cell does use pyruvate in the krebs cycle constantly but if there are too many pyruvate compounds then some of them don't make it into the krebs cycle and are turned into acetaldehyde and further into ethanol.

 

[ajdelange]

No, the fate of pyruvate under fermentation is as given in #11. It would only enter the Krebs cycle if respiration gets going for some reason.

 

[helgibelgi]

Definitely on the right track here though rather than say that protein is required you might want to say that nitrogen and amino acids which contain nitrogen (though they come from proteolysis of the malt) are needed. The yeast will then synthesize the amino acids (and proteins and nucleotides) from the available nitrogen. Most commercial yeast 'nutrients' contain a large proportion of urea and diammonium phosphate the latter of which provides both the the nitrogen and phosphorous for ATP, ADP, NAD etc.

Yes, I think so.



As was pointed out in #10 it goes to sterol formation.




The pyruvate is non oxidatively decarboxylated:

CH3COCOOH --> CH3CHO + CO2

giving acetaldehyde which is then reduced to ethanol by NADH.

Sweet, thanks! I clearly need to study the oxygen use better, but the rest seems to be pretty clear to me. Still a little unsure about krebs cycle vs. ethanol production regarding why the cell would choose one over the other pathway. Is it because the cell needs oxygen to create ATP by oxidative phophorylation? and therefore choose this pathway under aerobic condtions?

 

[helgibelgi]

No, the fate of pyruvate under fermentation is as given in #11. It would only enter the Krebs cycle if respiration gets going for some reason.

Does cellular respiration not happen at all? I was guessing that in the beginning, when the yeast has just entered the wort, that the cells would undergo cellular respiration in order to get a lot of energy for growth.

 

[ajdelange]

Not, IIRC, in the brewery. Yeast have been bred to ferment. They will, again memory is hazy, I think undertake respiration if sugars are depleted and oxygen is present using ethanol as the carbon source.

 

[orangehero]

There's the Crabtree effect

http://en.m.wikipedia.org/wiki/Crabtree_effect

 

[helgibelgi]

There's the Crabtree effect

http://en.m.wikipedia.org/wiki/Crabtree_effect

So because of the Crabtree effect, cellular respiration does not happen. The yeast cells are basically happy with the ATP generated from glycolysis alone, and pyruvate goes on into ethanol production.

I admit, I am a slow thinker. This was the second time someone pointed out the Crabtree effect, but only the second time around I think I'm starting to get it

 

[ArcLight]

So because of the Crabtree effect, cellular respiration does not happen. The yeast cells are basically happy with the ATP generated from glycolysis alone, and pyruvate goes on into ethanol production.

I admit, I am a slow thinker. This was the second time someone pointed out the Crabtree effect, but only the second time around I think I'm starting to get it

Its much more complex than that.
Fermentation is faster than respiration. In a nutrient rich environment yeast have evolved to want to consume this abundant food as quickly s possible, before competitors do. The by products of fermentation (ethanol and lowering the pH) are harmful to competitors.

If you want yeast to respire instead of ferment, try making a very weak starter of 0.3 Plato, and keep it aerated. That's just below the Crabtree threshold and the yeast wont ferment.

In aerated wort (i.e. - a nutrient rich environment), I don't know if the yeast both ferment and respire, at least until the O2 is used up.
Or maybe the fermentation shuts down the respiration pathway.
It might be that fermentation is a supressor of respiration.

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3396845/