Yeast
Introduction
Yeast is a type of fungus that has been utilized by humans for thousands of years due to its ability to ferment sugars. This property has made it indispensable in the production of bread, beer, and wine. Yeast is a eukaryotic organism, meaning its cells contain a nucleus and other organelles enclosed within membranes.
Classification
Yeast belongs to the kingdom Fungi and is classified under the phylum Ascomycota. The most commonly used species in baking and brewing, Saccharomyces cerevisiae, belongs to the class Saccharomycetes. Other species of yeast, such as Candida milleri and Candida holmii, are also used in certain types of fermentation.
Biology
Cell Structure
Yeast cells are typically round to oval in shape and are usually 5–10 micrometers in diameter. They have a cell wall composed of glucans and chitin, which provides structural support and protection. Inside the cell wall is the plasma membrane, which controls the movement of substances in and out of the cell.
Reproduction
Yeast can reproduce both sexually and asexually. Asexual reproduction occurs through a process called budding, where a small bud forms on the parent cell, grows to full size, and then separates. Sexual reproduction occurs when two yeast cells of opposite mating types fuse to form a zygote.
Metabolism
Yeast cells are facultative anaerobes, meaning they can metabolize sugars both in the presence and absence of oxygen. In the presence of oxygen, yeast undergoes aerobic respiration, which produces carbon dioxide and water as byproducts. In the absence of oxygen, yeast undergoes fermentation, which produces carbon dioxide and ethanol.
Uses
Baking
In baking, yeast is used as a leavening agent. The yeast ferments the sugars present in the dough, producing carbon dioxide gas. This gas gets trapped in the dough, causing it to rise and giving bread its characteristic texture.
Brewing
In brewing, yeast is used to ferment the sugars present in the wort (unfermented beer) to produce alcohol and carbon dioxide. Different strains of yeast are used to produce different styles of beer, with each strain contributing its own unique flavors and aromas.
Biotechnology
In biotechnology, yeast is used as a model organism for studying eukaryotic cell biology. It is also used in the production of biofuels, such as ethanol, and in the production of pharmaceuticals, such as insulin.
Health and Safety
While yeast is generally safe to consume, some people may have allergies or intolerances to it. In rare cases, yeast can cause infections in people with weakened immune systems. Additionally, the ethanol produced by yeast during fermentation can have harmful effects when consumed in excess.