How does fermentation happen

As with glycolysis, fermentation takes place in the cytoplasm of the cell. There are two different forms of fermentation— lactic acid fermentation and alcoholic fermentation.

Let's first take a look at lactic acid fermentation. Most organisms carry out fermentation through a chemical reaction that converts the pyruvate from glycolysis into lactic acid or lactate.

Humans undergo lactic acid fermentation when the body needs a lot of energy in a hurry. When you are sprinting full speed, your cells will only have enough ATP stored in them to last a few seconds. Fermentation makes it possible for cells to continue generating ATP through glycolysis. Lactic acid is a byproduct of fermentation. Lactic acid will build up in fermenting cells and eventually limit the amount of fermentation that can occur.

The only way to get rid of lactic acid is through a chemical pathway that requires oxygen. As a result, after a quick sprint, a runner will need to supply oxygen to cells with plenty of heavy breathing. An intense effort that lasts just a few seconds may require several minutes of heavy breathing to deliver enough oxygen to cells to clear the lactic acid build up. Yeast a microscopic fungus are also capable of both cellular respiration and fermentation.

When yeast cells are kept in an anaerobic environment i. However, alcoholic fermentation in yeast produces ethyl alcohol instead of lactic acid as a waste product. Alcoholic fermentation also releases carbon dioxide. Alcoholic fermentation is the process that causes bread dough to rise. When yeast cells in the dough run out of oxygen, the dough begins to ferment, giving off tiny bubbles of carbon dioxide.

These bubbles are the air spaces you see in a slice of bread. The small amount of ethyl alcohol that is produced in the dough evaporates when the bread is baked. Directions : Watch Bread Time Lapse to see the results of fermenting yeast cells producing carbon dioxide. Skip to main content. When he compared the sediments from different containers under the microscope, he noticed that large amounts of yeast were visible in samples from the containers in which alcoholic fermentation had occurred.

In contrast, in the polluted containers, the ones containing lactic acid, he observed "much smaller cells than the yeast. Alcoholic fermentation occurs by the action of yeast; lactic acid fermentation, by the action of bacteria. By the end of the nineteenth century, Eduard Buchner had shown that fermentation could occur in yeast extracts free of cells, making it possible to study fermentation biochemistry in vitro.

He prepared cell-free extracts by carefully grinding yeast cells with a pestle and mortar. The resulting moist mixture was put through a press to obtain a "juice" to which sugar was added. Using a microscope, Buchner confirmed that there were no living yeast cells in the extract. Upon studying the cell-free extracts, Buchner detected zymase, the active constituent of the extracts that carries out fermentation. He realized that the chemical reactions responsible for fermentation were occurring inside the yeast.

Today researchers know that zymase is a collection of enzymes proteins that promote chemical reactions. Enzymes are part of the cellular machinery, and all of the chemical reactions that occur inside cells are catalyzed and modulated by enzymes.

ATP is a versatile molecule used by enzymes and other proteins in many cellular processes. Glycolysis — the metabolic pathway that converts glucose a type of sugar into pyruvate — is the first major step of fermentation or respiration in cells. It is an ancient metabolic pathway that probably developed about 3. Because of its importance, glycolysis was the first metabolic pathway resolved by biochemists. The scientists studying glycolysis faced an enormous challenge as they figured out how many chemical reactions were involved, and the order in which these reactions took place.

In glycolysis, a single molecule of glucose with six carbon atoms is transformed into two molecules of pyruvic acid each with three carbon atoms. In order to understand glycolysis, scientists began by analyzing and purifying the labile component of cell-free extracts, which Buchner called zymase. They also detected a low-molecular-weight, heat-stable molecule, later called cozymase. Both components were required for fermentation to occur. The complete glycolytic pathway, which involves a sequence of ten chemical reactions, was elucidated around In glycolysis, two molecules of ATP are produced for each broken molecule of glucose.

During glycolysis, two reduction-oxidation redox reactions occur. In a redox reaction, one molecule is oxidized by losing electrons, while the other molecule is reduced by gaining those electrons. A molecule called NADH acts as the electron carrier in glycolysis, and this molecule must be reconstituted to ensure continuity of the glycolysis pathway. Figure 3: Alternative metabolic routes following glycolysis A budding yeast cell is shown with the aerobic and anaerobic metabolic pathways following glycolysis.

The nucleus black and mitochondrion red are also shown. When oxygen is available, pyruvic acid enters a series of chemical reactions known as the tricarboxylic acid cycle and proceeds to the respiratory chain.

As a result of respiration, cells produce 36—38 molecules of ATP for each molecule of glucose oxidized. In the absence of oxygen anoxygenic conditions , pyruvic acid can follow two different routes, depending on the type of cell. It can be converted into ethanol alcohol and carbon dioxide through the alcoholic fermentation pathway, or it can be converted into lactate through the lactic acid fermentation pathway Figure 3.

Since Pasteur's work, several types of microorganisms including yeast and some bacteria have been used to break down pyruvic acid to produce ethanol in beer brewing and wine making. The other by-product of fermentation, carbon dioxide, is used in bread making and the production of carbonated beverages. Humankind has benefited from fermentation products, but from the yeast's point of view, alcohol and carbon dioxide are just waste products.

As yeast continues to grow and metabolize sugar, the accumulation of alcohol becomes toxic and eventually kills the cells Gray This is why the percentage of alcohol in wines and beers is typically in this concentration range. However, like humans, different strains of yeast can tolerate different amounts of alcohol.

Therefore, brewers and wine makers can select different strains of yeast to produce different alcohol contents in their fermented beverages, which range from 5 percent to 21 percent of alcohol by volume.

For beverages with higher concentrations of alcohol like liquors , the fermented products must be distilled. Today, beer brewing and wine making are huge, enormously profitable agricultural industries. These industries developed from ancient and empirical knowledge from many different cultures around the world. Today this ancient knowledge has been combined with basic scientific knowledge and applied toward modern production processes.

These industries are the result of the laborious work of hundreds of scientists who were curious about how things work. Barnett, J. A history of research on yeast 1: Work by chemists and biologists, — Yeast 14 , — A history of research on yeast 2: Louis Pasteur and his contemporaries, — Yeast 16 , — A history of research on yeast 3: Emil Fischer, Eduard Buchner and their contemporaries, — Yeast 18 , — Encyclopaedia Britannica's Guide to the Nobel Prizes Godoy, A.

Gray, W. Studies on the alcohol tolerance of yeasts. Journal of Bacteriology 42 , — Huxley, T. Popular Lectures and Addresses II. Chapter IV, Yeast This process is essential because it removes electrons and hydrogen ions from NADH during glycolysis. The effect is to free the NAD so it can participate in future reactions of glycolysis. The net gain to the yeast cell of two ATP molecules permits it to remain alive for some time. However, when the percentage of ethyl alcohol reaches approximately 15 percent, the alcohol kills the yeast cells.

Yeast is used in both bread and alcohol production. Alcohol fermentation is the process that yields beer, wine, and other spirits. However, it is becoming increasingly clear that genetically-modified microorganisms behave differently when they are grown in a laboratory flask or industrial brewers.

One factor causing this divergent behavior is the difference in physical stress they encounter. Recall the most recent time you went swimming. Do you remember experiencing lower pressure at the water surface and rising pressure when you go deeper into the pool? This also happens to microorganisms swimming in large brewer. Microorganisms at the bottom experience much greater hydrostatic pressure. When this happens, they can burst and die. Others could undergo genetic or metabolic changes, thus sabotaging previous genetic engineering efforts.

This is a huge problem for the food industry. Researchers have tried to address this problem by building microfluidic bioreactors that can handle volumes up to a few liters.

These microfluidic bioreactors function just like an industrial brewer but as a scaled-down version. Microorganisms can be grown in these scaled-down bioreactors and subject to different sensor-controlled pressures, stirring rates, temperatures, and pH. Next, by collecting data on the growth of microorganisms and product yield under these conditions, researchers can use this information to optimize fermentation in a scaled-up brewer. This can help realize industrial-scale production of new fermentation recipes.

Our sense of smell and taste are intricately connected. Unfortunately, because of this, some people avoid tasty fermented food because of its smell. What if there is a way to remove the pungent smell while maintaining the tastiness of fermented food? This motivated Yan et al. Electronic nose is basically an array of electronic sensors that create unique electrical signatures when different compounds bind to them.

These signatures are then fed and matched to a database of tested compounds. Using their technology, Yan and colleagues attributed the pungent smell of shrimp paste to propanoic acid. Similarly, Harper and co-workers also found using electronic nose that the aroma of cheese can be completely attributed to just five types of fatty acids.