Yeast

Yeast is a tiny living thing.

It is a type of fungus. Most yeasts are just one cell.

These tiny cells can make more cells. They often grow a small bud. This bud grows into a new cell.

Some yeast eats food like sugar. This makes air and bubbles.

These bubbles help bread rise.

People have used yeast for a long time. They found it in old ruins. It can help make bread and drinks.

Some yeast lives in the soil. Other yeast lives on fruit skins. It is all around us.

Yeast is a type of fungus. Most yeasts are made of just one cell.

These tiny living things can be very small. Most are only 3 to 4 micrometers wide. Some can grow to 40 micrometers.

Yeasts make more cells in a few ways. Many use budding. A small bud grows on the parent cell. The parent cell's center splits to help the bud. Then the bud grows and breaks off. This creates a new, smaller cell.

Other yeasts use fission. This makes two cells that are the same size.

One famous yeast is called Saccharomyces cerevisiae. It eats sugar to make food. This way of making food is called fermentation. During this, it lets out carbon dioxide and alcohol.

People use these for baking bread or making drinks. This has happened for thousands of years.

Yeasts live in many places. You can find them in soil or on fruit skins. Some live in the ocean. These are called marine yeasts. They can even live on human skin.

Yeast is a type of fungus that is mostly made of just one cell.

These tiny living things are everywhere in our world. Most yeasts are very small, measuring only 3 to 4 micrometers across. However, some species can grow as large as 40 micrometers. They belong to a huge group of living things called eukaryotes. There are at least 1,500 different species of yeast known today. They make up about 1% of all the different fungi we have described.

Most yeasts grow by a way called budding. This is a type of asexual reproduction where a small bud grows on the parent cell. The center of the parent cell splits to create a new center for the bud. Once the bud grows enough, it breaks away to become its own cell. This new daughter cell is usually smaller than its mother.

Some yeasts use a different way called fission. In fission, the cell splits to make two daughter cells that are the same size. Some yeasts can even grow into long strings of connected cells. These strings are called pseudohyphae, which means "false hyphae."

Humans have used yeast for thousands of years.

One famous species is called Saccharomyces cerevisiae. This yeast eats sugars like glucose or sucrose to get energy. Through a process called fermentation, it turns those sugars into alcohol and carbon dioxide. This is how bread rises and how certain drinks are made.

In 1680, a man named Anton van Leeuwenhoek first saw yeast under a microscope. He did not think they were alive at first. Later, in 1837, Theodor Schwann recognized that they were actually fungi. In 1857, Louis Pasteur proved that fermentation was caused by living yeast.

There are many ways to find and use yeast today.

In 1876, Charles L. Fleischmann showed a new way to sell yeast in Philadelphia. Before this, people mostly used yeast that was just floating in the air. Now, we can buy yeast as a dry powder or even as solid blocks. Some yeasts are even used in science to study how human cells work. Other species, like Candida albicans, can cause infections in people.

Scientists are also looking at using yeast to create electricity in special fuel cells.

Yeasts live in many different homes around the Earth.

You can find them on the skins of fruits like grapes or apples. Some live in the soil or even inside the bodies of insects and mammals. There are even yeasts that live in the deep ocean.

These are called marine yeasts. Some of these can grow using seawater instead of fresh water. They can even help produce biofuels to power machines. It is amazing how such tiny cells can do so much for our world.

Yeast refers to any species of fungus that grows primarily in a unicellular form. This means most yeast cells consist of just a single cell. These organisms are eukaryotes, which means their cells contain a nucleus. While they are tiny, they are incredibly diverse. There are at least 1,500 recognized species of yeast today. They make up about 1% of all described fungal species.

Although most are single-celled, some species can develop multicellular characteristics. They might form strings of connected cells called pseudohyphae, or "false hyphae." Others can evolve into multicellular clusters with specialized organelle functions.

Most yeasts reproduce asexually through a process called mitosis. The most common method is asymmetric division, known as budding.

During budding, a small daughter cell or "bleb" forms on the parent cell. The nucleus of the parent cell splits, and one new nucleus moves into the bud. Once the bud grows large enough, it separates from the mother cell. The new daughter cell is usually smaller than the original parent. However, some species like Schizosaccharomyces pombe use fission. In fission, the cell splits into two daughter cells of equal size.

Yeasts are chemoorganotrophs, meaning they get energy from organic compounds. They do not need sunlight to grow. Instead, they consume sugars like glucose, fructose, sucrose, or maltose. Some species can even use pentose sugars like ribose. Depending on their needs, yeasts are either obligate aerobes, which require oxygen, or anaerobes. Many are facultative anaerobes, meaning they can use both aerobic and anaerobic methods for energy.

This ability to process sugar is vital for human industry. For example, Saccharomyces cerevisiae converts carbohydrates into carbon dioxide and alcohol through fermentation.

Humans have interacted with yeast for thousands of years. Archaeologists found evidence of yeast-raised bread in ancient Egyptian ruins. They also found vessels in Israel from 5,000 to 2,500 years ago that contained yeast colonies. These vessels likely held beer or mead. In 1680, Anton van Leeuwenhoek first observed yeast under a microscope. He did not realize they were living organisms at first. It was not until 1837 that Theodor Schwann recognized them as fungi.

Later, in 1857, Louis Pasteur proved that fermentation was caused by living yeast cells.

Industrial yeast production has changed significantly over time. By the late 18th century, two main brewing strains were identified: Saccharomyces cerevisiae and S. pastorianus. The Dutch began selling S. cerevisiae for bread in 1780. In 1825, a new method allowed yeast to be prepared as solid blocks. In 1876, Charles L. Fleischmann exhibited commercial yeast in Philadelphia. This helped move people away from using only naturally occurring airborne yeasts.

The invention of the mechanical refrigerator also helped brewers and winemakers. It allowed them to work outside of seasonal constraints and earthen cellars.

Yeasts live in many different environments across the planet. You can find them on the skins of fruits like grapes or peaches. They also live in soil, in the gut flora of mammals, and even in the deep sea.

Some yeasts are opportunistic pathogens, such as Candida albicans, which can cause human infections.

Other species, known as marine yeasts, live in the ocean. Some are obligate marine yeasts, meaning they are confined to saltwater. These marine yeasts can produce bioactive substances like vitamins and enzymes. Scientists are even using them to produce bioethanol using seawater.

Modern science uses yeast for much more than just food. Saccharomyces cerevisiae is a major model organism in cell biology. Researchers study it to understand the biology of eukaryotic cells and human biology.

Beyond biology, yeast is being used in technology. Some species help generate electricity in microbial fuel cells. Others are used in the biofuel industry to produce ethanol. Even in nature, yeasts play complex roles. Some produce "killer toxins" to eliminate competing strains. These toxins might one day have important medical applications for treating infections.