What Are the Three Types of Fermentation?

Fermentation is a process where microorganisms create a desired change in food or drink. Such changes may include additional health benefits, greater preservation, or flavor enhancements. Microbial fermentation has been used by humans for thousands of years, long before any of the science involved was understood. Our modern understanding of fermentation is thanks to the French chemist Loius Pasteur, who was the first to show definitively that the fermentation of alcohol was caused by the multiplication of living yeast. He also proved that there were multiple kinds of fermentation, and he is most well known for his pasteurization process in which milk products, wine, and others that are likely to contain organisms are heated for sterilization. This was a revolution for the food industry and is used for dairy products to this day.

Microbial fermentation occurs naturally within the gastrointestinal tract as food is decomposed by gut microbiota. This natural fermentation can result in the synthesis of vitamins B and K, and it also commonly results in the production of methane, carbon dioxide, hydrogen, and other intestinal gasses. The intensity of the process, and the results, will depend on the method of fermentation used. Here are the main types used by humans.

Lactic Acid Fermentation

Certain strains of yeast and other microbes can convert starch and sugar into lactic acid without needing heat. This is sometimes called anaerobic respiration since it doesn’t require oxygen. With aerobic respiration, the oxygen we breathe in allows us to continue extracting energy from glucose in a process called glycolysis. This typically happens in our muscles which expend adenosine triphosphate (ATP) during contractions. During strenuous activity, like exercise, our muscles expend ATP faster than oxygen can resupply it, which makes anaerobic respiration necessary.

Lactic acid fermentation allows the body to continue breaking down glucose and produce ATP without oxygen, which is how your muscles can keep going even when you’re working to the point of being short on breath. Lactic acid bacteria also help to preserve certain foods and create new ones like pickles and sourdough bread.

Ethanol Fermentation

This is the type most people are likely familiar with as it produces alcohol. Yeasts or other bacteria break down glucose in starches and sugars, typically provided by agricultural crops, down into ethanol. This is the colorless liquid with the easily recognizable odor that makes up alcoholic beverages. Most fermentation processes result in broths that are 5% to 10% ethanol per volume, and it’s difficult to get higher than this because ethanol is toxic to the microbes that produce it.

Some facilities are able to produce higher concentrations thanks to using specialized yeasts. Stronger alcohol can also be produced by evaporating ethanol, repeated distillation, and dehydration.

Acetic Acid Fermentation

This is a process where the starches and sugars from fruit to turn them into sour condiments like vinegar. Acetic acid bacteria require oxygen to grow, so they generally aren’t found in anaerobic processes. It is still possible for them to grow on the surface of wine exposed to air. Some wineries use controlled exposure to oxygen to help speed up color stabilization, but exposing it to too much can result in spoilage.

The different types of fermentation can be broken into two basic categories: primary and secondary fermentation. Primary is a rapid process in which microbes work quickly on raw ingredients and produce a brine that prevents putrifying bacteria from reaching the ingredients. Secondary fermentation is a much longer process that can take a matter of weeks. Creating alcohol involves secondary fermentation methods where the food source for microbes (carbohydrates) become scarcer as the process goes on, and the ethanol produced eventually kills the bacteria.