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What is Fermentation?

By Brendan McGuigan
Updated May 21, 2024
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In a general sense, fermentation is the conversion of a carbohydrate such as sugar into an acid or an alcohol. More specifically, it can refer to the use of yeast to change sugar into alcohol or the use of bacteria to create lactic acid in certain foods. This process occurs naturally in many different foods given the right conditions, and humans have intentionally made use of it for many thousands of years.

The earliest uses of fermentation were most likely to create alcoholic beverages such as mead, wine, and beer. These beverages may have been created as far back as 7,000 BCE in parts of the Middle East. The fermentation of foods such as milk and various vegetables probably happened sometime a few thousand years later, in both the Middle East and China. While the general principle is the same across all of these drinks and foods, the precise methods of achieving it, and the end results, differ.

Beer is made by taking a grain, such as barley, wheat, or rye, germinating and drying it, and pulping it into a mash. This mash is then mixed with hot water, and some fermentation begins. After being further treated, the liquid is transferred to a vessel, where yeast is added to the mixture. This yeast “eats” the sugar present in the mash and converts it into carbon dioxide and alcohol. After a few weeks of fermentation and a further period of conditioning, the beer is ready to be filtered and consumed.

Wine is created using a similar method that also involves fermentation. Grapes are crushed to release the sugar-rich juices, which are then either transferred quickly away from the skins or left to rest for a time to absorb some of the flavor, tannins, and color of the skins. Yeast is then added, and the grape juice is allowed to ferment for a number of weeks, at which point it is moved to different containers and processed at a slower rate, and eventually aged or bottled.

Pickling foods, such as cucumbers, may be accomplished by submerging the vegetable one wants to pickle in a salty water solution with vinegar added. Over time, bacteria create the lactic acid that gives the food its distinctive flavor and helps to preserve it. Other foods can be pickled simply by packing them in dry salt and allowing a natural fermentation process to occur.

Milk can also be cultured, and people have been using this process with dairy products for nearly 5,000 years. It is speculated that early dairy products, such as yogurt, was the result of a natural processes that occurred when the milk was cultured by bacteria that dwelt in skin sacks used to store dairy. Yogurt these days is made by adding a number of special bacteria, such as L. acidophilus and L. bulgaricus to milk and keeping it at the proper temperature. The bacteria begin converting the sugar in the dairy to lactic acid, eventually creating what we know as yogurt.

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Discussion Comments

By anon310516 — On Dec 24, 2012

How is soy fermented?

By anon283371 — On Aug 04, 2012

Why does the rate of conversion of raw materials to produce a fermentation process vary during the beginning, middle and final stages of the process?

By anon205982 — On Aug 14, 2011

i just want to know why sucrose,maltose or dextrose is not use in alcohol fermentation? please answer!

By anon199515 — On Jul 23, 2011

which companies are into fermentation? I am working in india in fermentation.Please let me know which companies in india and in the world are working in fermentation.

By anon161363 — On Mar 19, 2011

what is a fermenter made out of? I wouldn't mind details, please.

By anon155899 — On Feb 25, 2011

I am doing research. I would just like to ask if what are the other alternatives that can I use to hasten the fermentation process except on molasses?

By anon144471 — On Jan 19, 2011

i am wondering why does fermentation happens.

By anon141691 — On Jan 11, 2011

This is a very useful text and it has helped me a lot. My tuition teacher will definitely accept this answer. Regards: Kausalyah

By anon138790 — On Jan 02, 2011

thank you so much. this info really helped me with my science project and thanks to you i will probably get first place at the science fair.

By anon129475 — On Nov 23, 2010

Which organism can carry out the process of fermentation?

By anon124545 — On Nov 06, 2010

what other ingredients other than yeast or sugar, that would be added to the fermenter?

By anon109173 — On Sep 06, 2010

Does fermentation happen only in microbes?

By anon102647 — On Aug 09, 2010

I want to ask what the do's and don'ts of fermentation are, and what the is the main example of fermentation?

Please help me because this is my report in chemistry.

By anon78696 — On Apr 19, 2010

What kind of science experiment or investigation can we do to do with fermentation?

By anon73054 — On Mar 25, 2010

how is aerobic and anaerobic related to fermentation?

By anon71074 — On Mar 17, 2010

Which product ferments quicker in yeast?

Water, starch, sucrose, or glucose.

By anon64090 — On Feb 05, 2010

What would i do for making fermentation fast?

By randolfh — On Jan 08, 2010

could i make wine out of sugar cane? if so, how do I prepare it?

By anon54755 — On Dec 02, 2009

fermentation is the process of breakdown of organic substances and reassembly into other substances.

By anon52127 — On Nov 11, 2009

how do i produce acetone from fermentation?? Any idea? thanks. please reply ASAP.

By anon51151 — On Nov 03, 2009

Cool fact: The chinese used to use fermented soybeans to treat skin infections (2,000 B.C)

By anon51013 — On Nov 02, 2009

i am doing a science project and i had to explain fermentation what it is and what it does.

By anon44284 — On Sep 06, 2009

I am making an organic fertilizer using molasses among other things. How do I speed up the fermentation process so there is no 'scum' left at the top of the bucket?

By anon37240 — On Jul 17, 2009

I don't know where you got that source from but if the enzymes stop working at 14% how come some wines are as high as 18% e.g. dessert wines, these are not fortified, they reach 18% purely through fermentation. i'll tell you a legitimate fact about fermentation, it is a exothermic reaction. meaning heat is given of as a byproduct from converting the sugar into alcohol/CO2

By anon35692 — On Jul 07, 2009

i am a second year bio tech student.now i want do my project on fermentation. so help me to do my projects. and what are the things have to done to finish my project successfully? Please answer me sir!

By anon26475 — On Feb 14, 2009

so what is the theory of how to make yogurt using bacteria?

please answer!

By dharanaresh — On Jan 10, 2009

what are the different physical parameters to be controlled in fermentation process (related to instrumentation engg) for automation using plc.

By anon21548 — On Nov 17, 2008

somerset,

While your most commonly used yeasts for table wines do indeed cease (or slow incredibly) when alcohol levels reach the low to mid teens, some wine and even ale yeasts can be coaxed into fermenting to more than 20%. A number of non-fortified wines can be purchased commercially in this range. For beers, one of the only commercial examples comes from Sam Adams, and is called Utopias.

By anon19997 — On Oct 23, 2008

I just want to say that a hydrometer is a good way to measure the alcohol content of liquids. Also, I just want to say thanks for this information. Even though I'm only 13, I know a lot. You guys got a really good thing going on her. You have a lot of information.

Sincerely, hardcoresoccergirl

By anon19700 — On Oct 17, 2008

Fermentation involves the endogenous electron acceptor to break down organic compounds.

By somerset — On Feb 16, 2008

An interesting fact about fermentation of wine is that enzymes that break down sugars into wine become inactivated when the level of alcohol reaches about 14%. This is the reason why wine, or any alcohol product created by fermentation is less than 14% alcohol.

Most familiar wine is made from grapes, but "sake" for instance is made from rice, and "mead" is made from honey. Other products are made by fermentation as well, such as pickles, sauerkraut and olives.

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