Is glycolysis the beginning part of fermentation, or does fermentation follow glycolysis?

I see conflicting information from different sources


"..Alcohol fermentation follows glycolysis, just like lactic acid fermentation..." <-- So glycolysis is preceding fermentation, not part of fermentation


" The Actual Fermentation Part

Glycolysis and fermentation are two separate processes. Glycolysis was explained briefly to give the reader an idea of the events leading up to fermentation and the starting conditions in terms of molecules available for reaction.....Going into the fermentation, the molecules NADH and pyruvic acid are present. " <--- so glycolysis is preceding fermentation, not part of fermentation.

Whereas these two links put glycolysis as part of fermentation, not a preceding stage before fermentation.


"Fermentation and cellular respiration begin the same way, with glycolysis" <-- glycolysis is part of fermentation, not preceding it.



"fermentation, which is a process that anaerobically generates ATP by performing glycolysis..." <-- fermentation includes glycolysis, so glycolysis is part of fermentation, not preceding it.

So, which is it?

Is it a)like khanacademy and study.com, or b)like honchemistry.wikispaces.com

I have heard the idea that glycolysis is independent, in that it can produce some (not much, but some), energy on its own, and it can happen without fermentation or cellular respiration following. Though when would glycolysis occur without fermentation or respiration following? And even if glycolysis is that independent, it may still be at the beginning of respiration and fermentation and not preceding it.

Wikipedia speaks in a contrary way..


"Before fermentation takes place, one glucose molecule is broken down into two pyruvate molecules. This is known as glycolysis." <-- so glycolysis is preceding fermentation, not part of it.

so the above quote from wikipedia suggests that glycolysis is not the beginning part of fermentation, but a step preceding it

whereas still on the fermentation wikipedia page, it says

"Fermentation is a metabolic process that converts sugar to acids, gases, or alcohol....The first step, glycolysis" <-- so glycolysis is part of fermentation.

Links on respiration are more unambiguous that glycolysis is part of respiration.. the links on fermentation vary a bit on whether glycolysis precedes fermentation or is part of it.

  • $\begingroup$ This would not be a natural distinction, it is symantical. The only way to state for sure would be if some universally accepted governing board declared it so. Or, if you're a student, it's what the teacher says, at least until after the exam! $\endgroup$ – bpedit Jan 23 '17 at 18:35
  • $\begingroup$ @bpedit But biologists have scientific journals.. Is there inconsistency even within a journal, with some papers defining it one way and some defining it the other way? $\endgroup$ – barlop Jan 23 '17 at 22:29
  • $\begingroup$ @barlop — There is no call to define it. Papers typically will have titles like "Delayed Lactose Fermentation by Enterobacteriaceae" (to quote a 1966 paper I found by Googling) and, for example,measure the amount of lactose converted to lactic acid or whatever in different strains (or more likely assay the activity of various enzymes). But this is not a question that concerns anyone in a field that has been moribund for the past 50 years. $\endgroup$ – David Jan 23 '17 at 22:52
  • $\begingroup$ The very popular college text from which I used to teach AP Biology, Biology, Campbell & Reece, uses fermentation to describe the entire process. I agree with @David below, that is probably the more standard approach. $\endgroup$ – bpedit Jan 23 '17 at 23:01

As @bpedit indicates in his comment, this is a semantic question — i.e. one regarding the meaning and usage of words. I will explain how I and others use these words and why. If you are convinced by my logic you will wish to use them in the same way, if not you are free to use them differently. However there is no ‘universal truth’ here, and if you are student I have no idea what your instructor thinks.

The problem is that ‘fermentation’ and ‘ferment’ (both as a noun and a verb) are old words, predating any understanding of the processes involved. Thus the Oxford English Dictionary quotes a relevant early example of the use of ‘ferment’ as a verb as follows:

1663 Cowley Verses, to Royal Society iv, All their juyce did .. Ferment into a .. refreshing Wine.

From this, it is clear that the idea of the fermentation process is the conversion of some initial compound (the sugar in the ‘juyce’) to some final compound (the alcohol in the wine). This usage is still current in referring to the process of fermentation, for example a Google search brings up a BBC Science educational page which states:

Beer and wine are alcoholic drinks made by fermentation reactions that use yeast to convert sugars into ethanol.

You may or may not be aware that term ‘ferment’ was historically used to mean what we now term yeast, and ‘Zwischenferment’, the obsolete German term for certain enzymes in yeast, is derived from this. So the original concept was merely of some biological conversion effected by yeast, although this has later been extended to bacteria and the idea changed to indicate metabolic processes capable of generating ATP anaerobically.

Part of the discrepancy in definition may be the emphasis on the end-product of the fermentation — ethanol fermentation, lactic acid fermentation etc. However, it seems clear to me that the fermentation is the whole chain of metabolic events from sugar (or whatever) to alcohol (or whatever); and if glycolysis is part of that process (which it is in this example) then glycolysis is part of the fermentation. (Of course, glycolysis can occur in other circumstances where the product, pyruvate, is oxidised in the tricarboxylic acid cycle, which is not a fermentation process.)


The extent to which one can tie oneself in knots with trying to define fermentation is illustrated in the best-selling and well-respected text book, originally written by Lubert Streyer and subsequently maintained by Berg et al. I mention this text both because an older edition is available on-line, and because a book of such value to the publishers is carefully vetted by referees. In the chapter on Glycolysis there is an attempt to define Fermentation:

Fermentation: An ATP-generating process in which organic compounds act as both donors and acceptors of electrons. Fermentation can take place in the absence of O2. Discovered by Louis Pasteur, who described fermentation as “la vie sans l’air” (“life without air”).

So the biochemical lawyers have produced a definition that very few readers will be able to take in at first sight. What is this business about electron donors and acceptors? Well what it means in relation to the fermentation process in which lactic acid is produced (note my legalistic choice of words) is that one organic compound is reduced (glyceraldehyde 3-phosphate) — by NAD+ — and one organic compound is oxidized (pyruvate) — by NADH. And as the production of ATP is included in the definition this means that Berg et al. include glycolysis in this definition of fermentation.

…except that on the same page there is the following statement:

pyruvate is converted, or fermented, into lactic acid in lactic acid fermentation or into ethanol in alcoholic fermentation

So here it seems that the word is being used for the conversion of pyruvate to lactate or ethanol, i.e. it excludes glycolysis.

Pasteur managed to talk about fermentation without being aware of glycolysis or ATP, and it is clear to me that you can write whatever carefully phrased definitions you like, but people are going to continue to use venerable terms like fermentation in whatever way seems natual to them.

  • $\begingroup$ I concur, that's the way in which I generally use the term. $\endgroup$ – bpedit Jan 23 '17 at 22:52
  • $\begingroup$ I see the definition apparently used by that statement from BBC science, is consistent with the old definition(that requires sugar be the start), and the new one(which mandates no electron transport chain). I see what you mean that a current usage, from BBC science, is using the new definition but is consistent with the old one, by including sugar at the start. $\endgroup$ – barlop Jan 24 '17 at 1:09
  • $\begingroup$ However, BBC science is a bit dodgy for example bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/… says "Anaerobic respiration in plant cells and some microorganisms (such as yeast) " <-- And that's wrong. Yeast mitochondia, are (like most eurkaryotic organisms's mitochondria), only capable of using oxygen as the terminal electron acceptor in their electron transport chain. So, like humans, yeast,cannot do anaerobic respiration. They do aerobic respiration, and they do fermentation. So I guess their definition of respiration is wrong? $\endgroup$ – barlop Jan 24 '17 at 1:14
  • $\begingroup$ @barlop — My quote from the BBC was just to show that the 17thC usage persists to the present day. I do not intend to cite the BBC as a scientific authority. However, perhaps it was late at night when you wrote "So, like humans, yeast,cannot do anaerobic respiration". The word "respiration" is a semantic minefield as in common usage it is equivalent to 'breathing", so "anaerobic respiration" seems an oxymoron. However biochemically respiration is used to mean obtaining energy from metabolism of nutrients, and anaerobic respiration is what fermentation (in yeast and bacteria) is all about. $\endgroup$ – David Jan 24 '17 at 11:17

Glycolysis is the beginning portion of BOTH types of respiration; aerobic and anaerobic. It makes a couple of ATP. If aerobic respiration occurs, it recharges more ATP. If anaerobic respiration occurs, the organism can make other compounds (like Lactic Acid) but doesn't generate any more ATP. I actually made a diagram that you might find helpful. It's posted here on Twitter:


And have now included it in this post below

enter image description here

I also made a series of videos for my students that might be useful as well. They're on Youtube: Below is a video on cellular respiration that goes into more detail.


  • $\begingroup$ Can you please not advertize yourself but write an answer, which stands for itself? So adding pictures here instead of linking them, for example. References are for further reading... $\endgroup$ – Chris Feb 9 '17 at 19:02
  • $\begingroup$ Thanks.. And I think this is the case of fermentation too. It'd be awesome if you can address this question too. biology.stackexchange.com/questions/55505/… $\endgroup$ – barlop Feb 9 '17 at 21:07
  • $\begingroup$ @Chris i'm not sure if it's possible to add pics sometimes, until rep is higher, but i've edited her post to add the picture from the link she gave, and i've put the references more in a context of sources and further information. It's great to have an educator contributing. $\endgroup$ – barlop Feb 9 '17 at 21:11
  • $\begingroup$ I think you're right it's part of the beginning of both. However, it's kind of wrong/questionable though to count fermentation under respiration, (which your diagram does) see my answer biology.stackexchange.com/questions/55505/… $\endgroup$ – barlop Feb 12 '17 at 3:06
  • $\begingroup$ I think you're right it's part of the beginning of both. However, it's kind of wrong/questionable though to count fermentation under respiration, (which your diagram does) see my answer that i've just posted here $\endgroup$ – barlop Feb 12 '17 at 3:19

I will post an answer that uses an advanced microbiology book, as they are careful to get their terms very accurate.

Glycolysis is part of both respiration and fermentation.

Microbiology: A Clinical Approach, Second Edition By Anthony Strelkauskas, Angela Edwards, Beatrix Fahnert, Greg Pryor, Jennifer Strelkauskas

enter image description here

(Side note- Non-introductory microbiology books don't count fermentation as part of respiration. As I discovered when looking into whether humans did anaerobic respiration, here Are humans capable of both anaerobic respiration, and lactic acid fermentation? And as is shown in the diagram above, from that advanced microbiology text. Biology 101 texts, and human biology texts, are more relaxed(arguably wrong), with their definition)


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