Fermentation

Fermentation is a natural process that helps living things make energy without needing oxygen. It happens when tiny particles called organic molecules, like sugar, are broken down by special tiny living things. This process makes a substance called adenosine triphosphate, which gives cells energy to work.

People have used fermentation for thousands of years to make and keep food safe to eat. It helps food taste better and stay fresh longer. Fermentation is also good for our health. The tiny living things in our stomachs use fermentation to help us get energy from the food we eat.

Fermentation is also used to make important products for factories, like ethanol, which is used in drinks such as beer and wine. This process can create many different products, showing just how useful and varied fermentation can be in nature.

Definition

Fermentation is a process where tiny living things break down food without using oxygen. One simple way to think about it is that the same food gives both the energy and the helper needed for the process. This is different from how our bodies get energy with oxygen or from some other processes that use things like minerals.

Long ago, a scientist named Louis Pasteur called this "life without air." Sometimes people also think of fermentation as a way to make energy by breaking down food in a special step. When we talk about making things on a big scale, like in factories, we call that industrial fermentation.

Biological role and prevalence

Fermentation helps living things make energy from sugars like glucose. It was not useful for the earliest life forms because the ocean did not have many complex sugars.

Fermentation does not need extra oxygen, so it can happen in any environment. However, it is not as efficient as other ways of making energy, producing only 2 to 5 energy units per glucose compared to 32 units with oxygen.

More than a quarter of bacteria and certain single-celled organisms use fermentation. It is common in some types of bacteria but rare in others. These microbes are often found inside hosts, like in the gut, as well as in sediments and food. They can produce many different end products, such as lactate, acetate, ethanol, and carbon dioxide (CO₂).

In humans, fermentation helps provide energy during short bursts of activity, like exercising, but can also occur in certain health conditions. It works for a short time before rest is needed.

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Substrates and products of fermentation

Fermentation is a special kind of chemical reaction that helps living things make energy. Microbes, like tiny living things, often use this process to turn simple sugars, such as those found in food, into useful products like energy and different acids. People have used fermentation for a very long time to help keep food fresh and to give it flavor and texture.

Common foods that use fermentation include bread, dairy products, rice, honey, and beer. Over time, people have learned to control this process to get specific flavors and textures in our food and drinks. For example, this is easy to see in the way beer is made.

Biochemical overview

When an organic compound goes through fermentation, it breaks down into a simpler molecule and releases electrons. These electrons move to a special helper molecule, which then passes them to another organic compound. This process makes ATP, the energy currency of cells, which can be created in two ways: through a direct method or with the help of a special enzyme.

When glucose is fermented, it first goes through a process called glycolysis or another pathway and turns into a molecule called pyruvate. From pyruvate, the process can go in different directions to make various end products, like lactate. Along the way, electrons are released and picked up by special helper molecules. Later, these helpers give the electrons to their final destination and get ready to start again. ATP is also made at several steps during this journey.

Biochemistry of individual products

Ethanol

Main article: Ethanol fermentation

Yeast and other tiny living things can change a sugar called pyruvate into ethanol and carbon dioxide. This makes bread rise because the carbon dioxide makes bubbles in the dough. Ethanol is also what makes drinks like wine and beer able to make people feel different. Ethanol can also be used as fuel in cars when mixed with gasoline. Some fish can use this process for energy when there isn’t enough oxygen.

Before fermentation, a sugar molecule called glucose breaks down into two pyruvate molecules. This process helps make energy for the living thing doing the fermenting.

History of bioethanol fermentation

Ethanol has been used as a fuel for many years. In 1826, an American inventor made ethanol from corn. During the California Gold Rush in the 1850s, people used ethanol as fuel for lamps. In 1895, an engineer showed that his engine could run on ethanol. The 1970s oil crisis made people interested again, and Brazil started using ethanol a lot. The United States began using it as a fuel additive in the 1980s and 1990s. Today, people are still looking for new ways to make ethanol.

• 1826: An American inventor made ethanol from corn.
• 1850s: Ethanol was used as fuel in the United States during the California gold rush.
• 1895: An engineer showed his engine could run on ethanol.
• 1970s: The oil crisis made people interested in ethanol again.
• 1980s–1990s: The United States started making ethanol as a fuel additive.
• 2000s–present: People are still looking for new ways to make ethanol.

Lactate

Pyruvate is used in a process called lactic acid fermentation. One sugar molecule can turn into two lactic acid molecules. This happens in our muscles when we need energy fast, like when we run. It also happens in some tiny living things that make yogurt sour.

Hydrogen gas

Main article: Fermentative hydrogen production

Some tiny living things can make hydrogen gas during fermentation. This helps them get ready to use energy again. Hydrogen gas can be used by other tiny living things.

Glyoxylate

Some tiny living things can use a process called glyoxylate fermentation to get nitrogen from a substance called glyoxylate.

Other

There are many other types of fermentation, like mixed acid fermentation and butanediol fermentation.

In the broader sense

In food and industry, any change made by a living thing in a container can be called fermentation. This includes making new proteins from plants, like tempeh, or making enzymes that help in many jobs, like making food taste better or cleaning clothes.

Modes of industrial operation

Most industrial fermentation uses batch or fed-batch methods, although continuous fermentation can save money if certain difficulties, like keeping things clean, are managed.

In a batch process, all the ingredients are mixed at the start, and the reactions happen without adding more. This method has been used for thousands of years to make bread and drinks. However, it can be costly because the container must be cleaned very thoroughly between uses. Batch fermentation has several stages. First, there is a period where cells get used to their surroundings; then a time when they grow quickly. As the food for the cells runs low, growth slows down, but the making of important products like antibiotics speeds up. This continues until most of the food is gone, and then the cells stop working.

Fed-batch fermentation is a change to the batch method where some ingredients are added during the process. This helps control the different stages better and can increase the production of important products. Fed-batch operations often happen between batch operations.

Open fermentation methods can avoid the high cost of cleaning between batches by using ways that prevent unwanted substances from growing. For example, some methods use special bacteria that live in very hot or salty conditions, which keeps other unwanted bacteria away. Another method adds a little water to solid materials, which is often used to make flavors, enzymes, and acids for food.

In continuous fermentation, ingredients are added and products are removed all the time. There are three types: chemostats, which keep nutrient levels the same; turbidostats, which keep the amount of cells the same; and plug flow reactors, where the mixture flows through a tube. If done well, this method can save money and keep the production going smoothly. However, it can be hard to keep things running steadily and to prevent contamination, and the setup is often complicated. Usually, the container needs to run for more than 500 hours to save money compared to batch methods.

History of the use of fermentation

People have used fermentation for a very long time, especially to make drinks. Records show it was used as early as 7000 to 6600 BCE in Jiahu, China, and later in India, ancient Egypt, Babylon, and many other places. Fermented foods were important in religions like Judaism and Christianity.

In the 1800s, scientists learned that tiny living things called yeast cause fermentation. A famous scientist named Louis Pasteur showed that yeast and other tiny organisms start the fermentation process. Later, in 1897, a scientist named Eduard Buechner discovered that even without living yeast, the liquids from yeast could still cause fermentation. This helped us understand that special substances called enzymes, made by these tiny organisms, are responsible for fermentation.

Since then, people have kept finding new ways to use fermentation to make many products, from food and drinks to medicines and chemicals. In recent years, fermentation has also been used to create foods that can help with health in many ways.

Circular economy

Researchers are studying how fermentation can help create a circular economy to fight climate change and meet growing resource needs. Today’s economy uses a lot of fossil fuels, which increases greenhouse gases and global temperatures. A circular economy would use renewable resources and reuse materials to reduce waste.

Fermentation uses materials from plants and waste to make new fuels and products. Common materials include sugars from crops like sugarcane and corn. Scientists are also looking at using waste materials like wood chips. Fermentation can turn organic waste into useful gases and materials, making processes more efficient and better for the environment. It is used to make fuels like ethanol from plant sugars and to produce important chemicals used in many products.