TLDR: Fermentation is a process that happens when tiny living organisms called microorganisms break down organic substances, like carbohydrates, without using oxygen. It's been used by humans since ancient times to make food and drinks like yogurt, pickles, wine, and beer. It's also used in industry to make chemicals, biofuels, enzymes, proteins, and pharmaceuticals.

Fermentation is a metabolic process that occurs when enzymes produced by microorganisms cause chemical changes in organic substances. In biochemistry, it specifically refers to the extraction of energy from carbohydrates without the presence of oxygen. But in food production, fermentation can refer to any process where microorganisms bring about a desirable change to a food or beverage. The science of fermentation is called zymology.

Microorganisms, like bacteria and yeast, use fermentation as their primary way of producing energy when there is no oxygen available. Humans have been using fermentation for thousands of years to make food and drinks. For example, fermentation is used to preserve foods like pickles and yogurt, as well as to make alcoholic beverages like wine and beer. Fermentation also occurs in the digestive systems of all animals, including humans.

In industrial settings, fermentation is used on a larger scale to produce chemicals, biofuels, enzymes, proteins, and pharmaceuticals. It can be done in different ways, such as batch fermentation, where all the ingredients are combined and the reactions proceed without any further input. There's also fed-batch fermentation, where some ingredients are added during the fermentation process. And continuous fermentation, where substrates are continuously added and final products are continuously removed.

Fermentation has a long history and has played a crucial role in the development of human civilization. It has been used to make food and drinks since ancient times, and its importance in industry has only grown over the years. Advances in fermentation technology have led to the production of a wide range of consumer goods, from food and beverages to industrial chemicals and pharmaceuticals.