How Does Alcohol Fermentation Work

We often take nature for granted—the leaves that drop from trees compost to feed the trees, manure from animals feeds the earth on which it falls, water evaporates from lakes and rivers to create rain which feeds the lakes and rivers, and so forth. We know things work, but we don’t necessarily ask why or how. In our series on how fermentation works, Andrew continues with alcoholic fermentation.

If this is your first time joining us for the science of fermentation, please read the previous two posts on the subject. The first explains why our little microorganism friends ferment for us (article found here). The second article discusses the type of fermentation that most of us at Fermentoolsuse on a daily basis: lactic acid fermentation (find that post here).

So, if you’re all caught up now, let’s get going on the second type of fermentation—alcoholic fermentation.

How Does Alcohol Fermentation Work?

In General Terms

In this sort of fermentation, we start off with the same basic ingredient as in lactic acid fermentation: sugar. Just as before, the microorganisms responsible for alcoholic fermentation take each molecule of sugar, split it in half, and release just a bit of energy for it to use. However, from this point on, a different path is taken. Instead of converting that half-sugar into lactic acid, these microorganisms convert it into alcohol and carbon dioxide. Both of these two products are crucial in what we use alcoholic fermentation to make, so keep them in mind. Also, note that the purpose of this conversion is the same as before—to enable the chemical reaction that produces energy from sugar to continue.

A Bit Deeper

Get ready, fermentation-loving science nerds, for we are diving in. The first part of alcoholic fermentation, called glycolysis, and the uses of NAD+/NADH and ADP/ATP are identical to lactic acid fermentation, so I will not go into the detail I did previously. Again, be sure to check out that article if you need a refresher.

So, we are going to pick up from right after glycolysis. We have two half-sugar molecules called pyruvate and two other molecules, ATP and NADH. The ATP is the star of the show because it is used by the cell for energy so that it can do all of its cell-y things and stay alive. But in order to get more ATP, that NADH needs to be made back into NAD+. In order to do that, the cell takes the pyruvate and sends it through a few reactions. First, one carbon molecule breaks away from the pyruvate, joins with oxygen, and becomes carbon dioxide. The remaining part of what was pyruvate is now called acetaldehyde. This new molecule will accept an electron from the NADH which turns the NADH back into NAD+. However, the acetaldehyde is also not left unchanged; it becomes ethanol, also known as ethyl alcohol.

Where Does This Occur?

This sort of fermentation does not occur in humans (remember that lactic acid fermentation does occur in our bodies, though). If it did, every time we exercise, we would probably feel the effects of slight inebriation (instead of the burning that we currently feel). The major organism humans use for this sort of fermentation goes by the scientific name Saccharomyces or “sugar fungus.” Most of us would better recognize it by its more common name, yeast. And yeast is the star player in the production of a whole host of foods and beverages.

Remember that alcoholic fermentation has two products: ethanol and carbon dioxide. Different foods and beverages utilize different amounts of these products. Leavened bread utilizes the carbon dioxide to produce the texture we all love, while the alcohol is burned off during cooking. Wines from around the world allow the alcohol produced to accumulate while permitting the carbon dioxide to leave the fermentation vessel. And then products like beer want both the alcohol and the carbon dioxide to remain.

Benefits of Alcoholic Fermentation

As with all types of fermentation, alcoholic fermentation preserves the harvest. For example, grapes and apples last much longer as wine and cider than the fresh fruits or juices will. And of course, the health benefits of consuming alcoholic beverages, in moderation, of course, is well known and documented. Many studies over the decades (like this one) have shown that moderate alcohol consumption (wine, beer, or spirits) reduces the incidence of heart disease in men and women. This is one reason why some diets may be high in fats but still be heart healthy with the addition of an alcoholic drink (like the ever popular Mediterranean diet).

So with all that in mind, let’s raise a glass to our little friends, the yeasts, and all the good that they do for us through this marvelous process of alcoholic fermentation.


In the Fermentools store, you will find fermentation lids for Mason jars, glass weights, and that special Himalayan Powder salt that dissolves in cool water. Better yet, get a kit! Everything you need in one package.


Andrew and Michelle are the new owners of a 12-acre homestead in rural America. They are just embarking on this journey that is far removed from their city-life upbringing, so they realize that they have a lot to learn in order to succeed in this new place.Come along with them and read more about what they learn as they make this transition at their blog Simple Life Homestead.

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