Culinary Arts

What Is Fermentation? Learn About the 3 Different Types of Fermentation and 6 Tips For Homemade Fermentation

Written by MasterClass

Jun 5, 2019 • 6 min read

Humanity has been fermenting food since the Neolithic age, long before people understood the science behind the process. Today, following the scientific discoveries of French microbiologist Louis Pasteur, who showed that living organisms initiate fermentation, we know why fermentation not only makes food like sourdough bread, cheese, and wine taste better, but also helps to keep us alive.


What Is Fermentation?

Fermentation is any metabolic process in which microorganisms’ activity creates a desirable change in food and beverages, whether it’s increasing flavor, preserving foodstuffs, providing health benefits, or more.

The word “ferment” comes from the Latin verb “fervere,” which means “to boil.” Ironically, fermentation is possible without heat.

How Does Fermentation Work?

To master fermentation, you need to understand the science behind the chemical process.

  • Microorganisms survive using carbohydrates (sugars, such as glucose) for energy and fuel.
  • Organic chemicals like adenosine triphosphate (ATP) deliver that energy to every part of a cell when needed.
  • Microbes generate ATP using respiration. Aerobic respiration, which requires oxygen, is the most efficient way to do that. Aerobic respiration begins with glycolysis, where glucose is converted into pyruvic acid. When there’s enough oxygen present, aerobic respiration occurs.
  • Fermentation is similar to anaerobic respiration—the kind that takes place when there isn’t enough oxygen present. However, fermentation leads to the production of different organic molecules like lactic acid, which also leads to ATP, unlike respiration, which uses pyruvic acid.
  • Depending upon environmental conditions, individual cells and microbes have the ability to switch between the two different modes of energy production.
  • Organisms commonly obtain energy anaerobically through fermentation, but some systems use sulfate as the final electron acceptor in the electron transport chain.

What Happens During the Fermentation Process?

Fermentation occurs in the absence of oxygen (anaerobic conditions), and in the presence of beneficial microorganisms (yeasts, molds, and bacteria) that obtain their energy through fermentation. If enough sugar is available, some yeast cells, such as Saccharomyces cerevisiae, prefer fermentation to aerobic respiration even when oxygen is abundant.

  • During the fermentation process, these beneficial microbes break down sugars and starches into alcohols and acids, making food more nutritious and preserving it so people can store it for longer periods of time without it spoiling.
  • Fermentation products provide enzymes necessary for digestion. This is important because humans are born with a finite number of enzymes, and they decrease with age. Fermented foods contain the enzymes required to break them down.
  • Fermentation also aids in pre-digestion. During the fermentation process, the microbes feed on sugars and starches, breaking down food before anyone’s even consumed it.

What Are the Advantages of Fermentation?

Fermented foods are rich in probiotics, beneficial microorganisms that help maintain a healthy gut so it can extract nutrients from food.

  • Probiotics aid the immune system because the gut produces antibiotic, anti-tumor, anti-viral, and antifungal substances, and pathogens don’t do well in the acidic environment fermented foods create.
  • Fermentation also helps neutralize anti-nutrients like phytic acid, which occurs in grains, nuts, seeds, and legumes and can cause mineral deficiencies. Phytates also make starches, proteins, and fats less digestible, so neutralizing them is extremely beneficial.
  • Fermentation can increase the vitamins and minerals in food and make them more available for absorption. Fermentation increases B and C vitamins and enhances folic acid, riboflavin, niacin, thiamin, and biotin. The probiotics, enzymes, and lactic acid in fermented foods facilitate the absorption of these vitamins and minerals into the body.

What Are the 3 Different Types of Fermentation?

Microbes specialized at converting certain substances into others can produce a variety of foodstuffs and beverages. These are three distinct types of fermentation that people use.

  1. Lactic acid fermentation. Yeast strains and bacteria convert starches or sugars into lactic acid, requiring no heat in preparation. These anaerobic chemical reactions, pyruvic acid uses nicotinamide adenine dinucleotide + hydrogen (NADH) to form lactic acid and NAD+. (Lactic acid fermentation also occurs in human muscle cells. During strenuous activity, muscles can expend adenosine triphosphate (ATP) faster than oxygen can be supplied to muscle cells, resulting in lactic acid buildup and sore muscles. In this scenario, glycolysis, which breaks down a glucose molecule into two pyruvate molecules and doesn’t use oxygen, produces ATP.) Lactic acid bacteria are vital to producing and preserving inexpensive, wholesome foods, which is especially important in feeding impoverished populations. This method makes sauerkraut, pickles, kimchi, yogurt, and sourdough bread.
  2. Ethanol fermentation/alcohol fermentation. Yeasts break pyruvate molecules—the output of the metabolism of glucose (C6H12O6) known as glycolysis—in starches or sugars down into alcohol and carbon dioxide molecules. Alcoholic fermentation produces wine and beer.
  3. Acetic acid fermentation. Starches and sugars from grains and fruit ferment into sour tasting vinegar and condiments. Examples include apple cider vinegar, wine vinegar, and kombucha.

What Are the Different Stages of the Fermentation Process?

Depending upon what you’re fermenting, the process can have several stages.

  • Primary fermentation. In this brief phase, microbes begin rapidly working on raw ingredients such as fruit, vegetables, or dairy. The microbes present or in the surrounding liquid (such as brine for fermented vegetables) prevent putrefying bacteria from colonizing the food instead. Yeasts or other microbes convert carbohydrates (sugars) into other substances such as alcohols and acids.
  • Secondary fermentation. In this longer stage of fermentation, which lasts several days or even weeks, alcohol levels rise and yeasts and microbes die off and their available food source (the carbohydrates) becomes scarcer. Winemakers and brewers use secondary fermentation to create their alcoholic beverages. The pH of the ferment can differ significantly from when it started out, which affects the chemical reactions taking place between the microbes and their environment. Once alcohol is between 12–15% and it kills the yeast, preventing further fermentation, distillation is needed to remove water, condensing alcohol content to create a higher percentage of alcohol (proof).

6 Tips for Starting Fermentation

Whether you’re looking to pickle vegetables or begin brewing beer at home, these tips will help you start fermenting.

  1. Establish your “starter” cultures. Microbes are naturally present in the air you breathe, but to begin fermentation you will often need a “starter” set of cultures, such as whey (from yogurt), a Symbiotic Colony of Bacteria and Yeast, or SCOBY (for kombucha), or even liquid from a previous ferment. Starter cultures are already rich with beneficial microorganisms. When you add them to your food or beverage product, they’ll multiply rapidly and jump-start the fermentation process.
  2. Keep your equipment clean. To prevent bad bacteria from leaching onto your ferment, it’s essential that you clean and sterilize your kitchen equipment and the surfaces that you work on.
  3. Avoid exposure. Exposing your ferment to air can prevent proper fermentation from taking place and increase the risk of spoilage and food poisoning. There are several ways you can avoid that.
  4. To prevent fermenting food from coming into contact with air, you can submerge it in a salt solution (brine). When fermenting solid pieces of food like chopped vegetables, this method works well. You can control the pH of the fermentation, which determines how much oxygen will be present, by adding vinegar to your solution.
  5. Storage. To avoid air contamination, you should keep your fermenting product in a sealable storage container. Many home fermenters use a simple mason jar with a lid to lock out air, but there are other alternatives. Typically, storage containers have a valve to vent carbon dioxide gas released during fermentation. If you are committed to carefully monitoring your ferment so it doesn’t spoil, you can alternatively open sealed containers manually to release the carbon dioxide. (If you are making kombucha, wine, or other end products that benefit from carbonation, you can forgo the CO2 venting.)
  6. Fermentation management. By controlling the temperature of the environment, you can affect the outcome of your fermentation. Typically, microbes work well when their environment is warm or room temperature, but the ideal temperature depends upon the type of microbes you’re using and what you’re fermenting. Altering the temperature can impact your process greatly. Moving your product to a cooler environment, such as a basement or a refrigerator, will slow the rate of fermentation and, in some cases, halt it completely. Heating a ferment, on the other hand, can kill your essential microbes.

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