Scientists Say: Fermentation

This process breaks down carbohydrates, such as sugars, to produce gases, acids or alcohol

Some bacteria ferment the sugars in milk, making lactic acid. This creates yogurt.

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Fermentation (noun, “FUR-men-TAY-shun”)

This word describes a process by which living things break down carbohydrates to make other molecules and provide energy to cells or organs. Carbohydrates are common compounds in food and include sugars and starches  Some microbes use fermentation to get energy from carbohydrates. When people put those microbes to work, this process helps make both food and fuels. 

Fermentation makes acids, alcohols, gases and other chemicals. A microbe called yeast, for example, ferments the sugars in bread dough. This makes the gas carbon dioxide. Bubbles of that gas make a loaf of bread rise and become light and fluffy. Yeast also make the alcohol in wine and beer. 

People can use fermentation to make alcohol for fuels. For instance, bacteria and yeast can break down sugars and starches from plants, such as corn. That fuel can be added to gasoline to help power cars.    

The microbes in animal guts, including in our own guts, ferment. When cows digest grass, some of their gut microbes make methane gas. That gas escapes when they belch or fart. That might sound funny, but methane is a greenhouse gas. It traps heat and contributes to global warming.  

Fermentation isn’t just for microbes. Our muscles can also ferment. Animal muscles usually get energy from a process that uses oxygen. When they can’t get enough oxygen, they use fermentation. That’s because fermentation doesn’t require oxygen. 

In a sentence

Like those of cows, kangaroo farts can contain methane because of fermentation by their gut microbes.  

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Carolyn Wilke is a staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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