Fermentation Science

Fermentation is an anaerobic metabolic process where pyruvate produced in glycolysis is reduced to an end product, allowing NADH to be oxidized back to NAD+. ^[1] That last part matters more than it sounds. NAD+ is like a molecular shuttle bus that cells desperately need to keep running. Without it, glycolysis stops. The cell dies. So fermentation doesn't exist to make beer or yogurt taste interesting — it exists to keep that shuttle bus moving when oxygen isn't around. ^[2]

Here's where the alchemy happens. Microorganisms such as yeast and bacteria utilize fermentation processes. ^[3] But they're not just passengers. They're the catalysts that make the whole system work. Inside the cell, fermentation uses substrate-level phosphorylation to produce ATP, without an electrochemical gradient. ^[4] That's different from how cells normally generate energy with oxygen present. It's a workaround. A clever one, but fundamentally different.

Now, different microorganisms produce different end products depending on which fermentation pathway they use. In yeasts, the end product of anaerobic respiration is ethanol. ^[5] In animal cells, the end product is lactic acid. ^[5] But the most common industrial pathway is alcoholic fermentation, where yeast cells ferment sugars to produce ethanol and CO2. ^[6] That process unfolds in precise steps. Glycolysis converts glucose to pyruvate. Pyruvate then undergoes decarboxylation to acetaldehyde, releasing CO2 in the process.

Lactic acid fermentation is another key pathway. ^[6] But whether we're talking about yeast producing alcohol or bacteria producing acid, the common fermentation end products include ethanol, lactic acid, and carbon dioxide. ^[6] These aren't waste products in the biological sense — they're the necessary output of a cell's effort to survive without oxygen.

What ties all this together is purpose. Fermentation pathways are essential for ensuring an adequate supply of NAD+ for glycolysis to continue and harvest ATP. ^[2] The metabolic alchemy is real. Sugar enters. Microorganisms transform it through precise chemical steps. Energy emerges on one end. Ethanol, lactic acid, or CO2 emerges on the other. And that's before we even talk about what happens when humans harness these pathways for food and drink.

That metabolic dance yeast performs—breaking sugar into energy and alcohol—has been quietly reshaping human civilization for longer than we might think. The story of fermentation isn't just biochemistry. It's a thread connecting ancient survival to modern medicine.

Fermentation history begins as far back as 10,000 BCE, emerging with the first human civilization in the Fertile Crescent. ^[7] Those early people didn't understand what yeast was doing at the molecular level. But they knew that leaving milk or fruit exposed to air transformed it—sometimes into something spoiled, sometimes into something better. By 7000 BCE, fermentation was used in food production for preservation of milk, fruits, and vegetables, and to produce beverages, cheeses, bread, pickled foods, and vinegar. ^[8] This wasn't accident. It was discovery, refined through generations into reliable technique. Early human ancestors utilized fermentation to create foods like cheese, yoghurt, and bread, as well as alcoholic drinks such as beer and wine. ^[9] These foods did more than taste good—they kept. In a world without refrigeration, fermentation meant calories that survived the winter.

For thousands of years, fermentation remained a craft. Nobody knew why it worked. Then in the 1800s, Louis Pasteur discovered that live yeast causes fermentation. ^[10] That single insight unlocked everything. Once scientists understood the organism behind the process, they could control it, scale it, optimize it. The foundation for industrial fermentation was laid in the 19th century. ^[8]

What emerged from that foundation transformed entire industries. Industrial microbiology saw high titers achieved in fermentation, such as 170 g/l L-lysine-HCl, and the discovery of monosodium glutamate fermentation in Japan in 1957 by Kinoshita, Udaka, and Shimono. ^[11] These weren't small improvements—they were breakthroughs that made industrial-scale production economically viable. Industrial fermentation is a large-scale biotechnological process employing microorganisms to generate useful compounds for sectors including medicines, food and beverages, biofuels, and chemicals. ^[12]

Today, fermentation has become the engine of biotechnology itself. Microbial fermentations are widely used for producing pharmaceuticals, including antibiotics, hormones, and vaccines. ^[13] Modern biotechnology leverages microbial fermentations for the production of biofuels and biogas. ^[13] The creation and optimization of microbial cell factories and fermentation processes enable the development of novel solutions for societal challenges, including the production of novel materials. ^[14]

What began with bread dough rising in ancient kitchens now drives the creation of life-saving drugs and sustainable alternatives to fossil fuels. The microbes haven't changed. Only our ability to harness them has.

Thanks for listening to this VocaCast briefing. Until next time.