Fermentation is a natural process for generating energy in anaerobic environments. Microorganisms like yeast and lactic acid bacteria (LAB) are known for their fermentation flair.
About Fermentation
Fermentation is essential in environments where oxygen is scarce. It can be deep in soil, in muscle tissue or sealed vats used for food production.
Organisms like yeast and lactic acid bacteria use fermentation to prosper in anaerobic environments. Their abilities are used in production of food and beverages for millennia.
Yeast Fermentation
Yeast transforms sugar into energy through alcoholic fermentation. The process begins as yeast cells consume glucose, a simple sugar sourced from carbohydrates. Glucose is the fundamental monosaccharide.
The first step is glycolysis. Glycolysis is a common metabolic pathway shared by aerobic and anaerobic organisms. Glucose, a six-carbon sugar, reduces to two three-carbon molecules of pyruvate.
These produce a small amount of ATP (adenosine triphosphate). ATP molecules are energy units of the cell. Glycolysis also produces NADH (nicotinamide adenine dinucleotide), an energy-carrying molecule.
A single cell uses about 10 million ATP molecules per second. It recycles all its ATP molecules every 20-30 seconds.
After glycolysis, yeast cells convert the pyruvate into ethanol, carbon dioxide and esters. This conversion generates energy and contributes to well-known flavors and aromas.
Lactic Acid Fermentation
Lactic acid bacteria like Lactobacillus and Streptococcus spp partake in lactic acid fermentation. They convert sugars into lactic acid, producing different flavors and textures.
Pyruvate is directly reduced to lactic acid (lactate) by the enzyme lactate dehydrogenase, again regenerating NAD+. This type of fermentation is valued for its tangy flavor, crunchy texture and preservation potential.
Lactic acid lowers pH, preserving food products while intensifying flavor. Yogurt has a pH of around 4.0, acidic enough to inhibit harmful bacteria and extend shelf life.
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