What are the products of alcohol fermentation?

Barnett, J. A. A history of research on yeast 1: Work by chemists and biologists, 1789–1850. Yeast 14, 1439–1451 (1998)

Barnett, J. A. A history of research on yeast 2: Louis Pasteur and his contemporaries, 1850–1880. Yeast 16, 755–771 (2000)

Barnett, J. A. & Lichtenthaler, F. W. A history of research on yeast 3: Emil Fischer, Eduard Buchner and their contemporaries, 1880–1900. Yeast 18, 363–388 (2001)

Encyclopaedia Britannica's Guide to the Nobel Prizes (2010)

Godoy, A., Herrera, T. & Ulloa, M. Más allá del pulque y el tepache: Las bebidas alcohólicas no destiladas indígenas de México. Mexico: UNAM, Instituto de Investigaciones Antropológicas, 2003

Gray, W. D. Studies on the alcohol tolerance of yeasts. Journal of Bacteriology 42, 561–574 (1941)

Huxley, T. H. Popular Lectures and Addresses II. Chapter IV, Yeast (1871). Macmillan, 1894

Jacobs, J. Ethanol from sugar: What are the prospects for US sugar crops? Rural Cooperatives 73(5) (2006)

McGovern, P. E. Uncorking the Past: The Quest for Wine, Beer, and Other Alcoholic Beverages. Berkeley: University of California Press, 2009

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Pasteur, L. Mémoire sur la fermentation alcoolique.Comptes Rendus Séances de l'Academie des Sciences 45, 913–916, 1032–1036 (1857)

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Meyerhof, O. & Junowicz-Kocholaty, R. The equilibria of isomerase and aldolase, and the problem of the phosphorylation of glyceraldehyde phosphate. Journal of Biological Chemistry 149, 71–92 (1943)

Meyerhof, O. The origin of the reaction of harden and young in cell-free alcoholic fermentation. Journal of Biological Chemistry 157, 105–120 (1945)

Meyerhof, O. & Oesper, P. The mechanism of the oxidative reaction in fermentation. Journal of Biological Chemistry 170, 1–22 (1947)

Pasteur, L. Mèmoire sur la fermentation appeleé lactique. Annales de Chimie et de Physique 3e. sér. 52, 404–418 (1858)

Page ID30629

Suzanne Wakim & Mandeep Grewal
Butte College

The muscles of this sprinter will need a lot of energy to complete their short race because they will be running at top speed. The action won't last long, but it will be very intense. The energy the sprinter needs can't be provided quickly enough by aerobic cellular respiration. Instead, a different process must be used by their muscle cells to power their activity.

Figure \(\PageIndex{1}\): Sprinter on the field

The cells of living things power their activities with the energy-carrying molecule ATP (adenosine triphosphate). The cells of most living things make ATP from glucose in the process of cellular respiration. This process occurs in three major stages, and one intermediate stage: glycolysis, oxidation of pyruvate, the Krebs cycle, and electron transport. The latter two stages require oxygen, making cellular respiration an aerobic process. There are also other ways of making ATP from glucose without oxygen, such as anaerobic respiration and fermentation, of making ATP from glucose without oxygen. Our cells do not perform anaerobic respiration. Therefore, we will only focus on fermentation in this section.

Figure \(\PageIndex{2}\). The picture shows glycolysis and fermentation. There are two types of fermentation, alcoholic and lactic acid. Fermentation follows glycolysis in the absence of oxygen. Alcoholic fermentation produces ethanol, carbon dioxide, and NAD+. Lactic acid fermentation produces lactic acid (lactate) and NAD+. The NAD+ cycles back to allow glycolysis to continue so more ATP is made. Each black ball in the image represents a carbon atom, and the red balls represent oxygen.

Fermentation starts with glycolysis, but it does not involve the latter two stages of aerobic cellular respiration (the Krebs cycle and oxidative phosphorylation). During glycolysis, two NAD+ electron carriers are reduced to two NADH molecules and 2 net ATPs are produced. The NADH must be oxidized back so that glycolysis can continue and cells can continue making 2 ATPs. The cells cannot make more than 2 ATP in fermentation because oxidative phosphorylation does not happen due to a lack of oxygen. There are two types of fermentation, alcoholic fermentation and lactic acid fermentation. Our cells can only perform lactic acid fermentation; however, we make use of both types of fermentation using other organisms.

Alcoholic fermentation The process by which this happens is summarized in Figure \(\PageIndex{2}\). The two pyruvate molecules are shown in this diagram come from the splitting of glucose through glycolysis. This process also produces 2 molecules of ATP. Continued breakdown of pyruvate produces acetaldehyde, carbon dioxide, and eventually ethanol. Alcoholic fermentation requires the electrons from NADH and results in the generation of NAD+.

Yeast in bread dough also uses alcoholic fermentation for energy and produces carbon dioxide gas as a waste product. The carbon dioxide that is released causes bubbles in the dough and explains why the dough rises. Do you see the small holes in the bread in Figure \(\PageIndex{3}\)? The holes were formed by bubbles of carbon dioxide gas.

Figure \(\PageIndex{3}\): Holes from carbon dioxide gas in bread dough are left behind after the bread bakes.

Lactic acid fermentation is carried out by certain bacteria, including the bacteria in yogurt. It is also carried out by your muscle cells when you work them hard and fast. This is how the muscles of the sprinter in Figure \(\PageIndex{1}\)get energy for their short-duration but intense activity. The process by which this happens is summarized in Figure \(\PageIndex{2}\). Again, two pyruvate and two ATP molecules result from glycolysis. Reduction of pyruvate using the electrons carried by NADH produces lactate (i.e. lactic acid). While this is similar to alcoholic fermentation, there is no carbon dioxide produced in this process.

Did you ever run a race, lift heavy weights, or participate in some other intense activity and notice that your muscles start to feel a burning sensation? This may occur when your muscle cells use lactic acid fermentation to provide ATP for energy. The buildup of lactic acid in the muscles causes the feeling of burning. The painful sensation is useful if it gets you to stop overworking your muscles and allow them a recovery period during which cells can eliminate the lactic acid.

With oxygen, organisms can use aerobic cellular respiration to produce up to 36 molecules of ATP from just one molecule of glucose. Without oxygen, some human cells must use fermentation to produce ATP, and this process produces only two molecules of ATP per molecule of glucose. Although fermentation produces less ATP, it has the advantage of doing so very quickly. It allows your muscles, for example, to get the energy they need for short bursts of intense activity. Aerobic cellular respiration, in contrast, produces ATP more slowly.

Myth: lactic acid build-up can cause muscle fatigue and a burning sensation in muscles. The soreness is thought to be due to microscopic damage to the muscle fibers.

Reality: The statement about lactic acid causing the burn in the muscle has no solid experimental proof. Alternate hypotheses suggest that through the production of lactic acid, the internal pH of the muscle decreases, triggering contraction in muscle due to the activation of motor neurons.

State the main difference between aerobic cellular respiration and fermentation.
What is fermentation?
Compare and contrast alcoholic and lactic acid fermentation.
Identify the major pro and the major con of fermentation relative to aerobic cellular respiration.
1. What process is shared between aerobic cellular respiration and fermentation? Describe the process briefly.
2. Why is this process able to occur in fermentation as well as aerobic respiration?
Which type of metabolic process occurs in the human body?
1. Aerobic cellular respiration
2. Alcoholic fermentation
3. Lactic acid fermentation
4. Both A and C
True or False. Lactic acid fermentation produces carbon dioxide.
True or False. Types of bacteria can carry out alcoholic fermentation and lactic acid fermentation.
True or False. No ATP is produced by fermentation.
Both lactic acid fermentation and alcoholic fermentation use which acid molecules to make their final products?
Which type of process is used in the making of bread and wine?
1. Alcoholic fermentation
2. Lactic acid fermentation
3. Aerobic cellular respiration
4. Prokaryotic respiration
Is fermentation an aerobic or anaerobic process?
What is the reactant, or starting material, shared by aerobic respiration and both types of fermentation?

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While many people think that Brewers are artisans for their production of beer, in actuality, the true craft and process of beer making are due to anaerobic glycolysis from yeast. Learn more here: