The Science of Fermentation

Fermentation is a chemical process that converts sugar found in fruits or grains to ethyl alcohol and carbon dioxide.

Wine, beer, and alcohol all begin with the basic fermentation process that uses a source of sugar in fruit or grains and yeast to begin the chemical process to break down the sugar into the other components. Alcoholic beverages or spirits take the additional step to distill the alcohol released from the fermentation process and removes the excess water from the alcohol until the desired percent (proof) is obtained. Yeast is used in the production of alcoholic beverages to provide the enzymes necessary for the fermentation process. During the fermentation process, sugar from either fruits or grains is converted through a chemical process to ethyl alcohol, CO₂, and water.

The fermentation process is also affected by other factors such as temperature and timing to determine the end results depending on what products are desired. Fermentation does not produce a beverage with greater than 12-15% alcohol because the yeast is killed by higher alcohol percentages. For an alcoholic product such as whiskey, distillation is required to remove water from the alcohol until the desired proof (strength or concentration) is obtained.

Wine may be the oldest alcoholic beverage known. Though yeast is mixed with grape juice to ferment and produce wine, it is a bit more complicated than you might imagine. Grapes are monitored in the vineyards to be harvested at the best time for ripeness and sugar content.

During harvest, grapes are sorted and quickly crushed to extract the juice. After crushing, the skins and pulp go through a press. For white wines, the skin and pulp is removed before the fermentation process begins. Red wine is made from dark grapes and the color comes from leaving the skins in during the fermentation process.

The longer the skins remain during the fermentation process the darker the wine. A Rose wine will be one in which the skins are removed after a few hours while a Red wine will sometimes take days. At the completion of the fermentation process, all the sugar in the wine is used and the resulting wine is said to be a dry wine.

For a sweet wine, the fermentation process is interrupted before all sugar is used, or a grape juice (must) will be added. Following fermentation, wine needs to mature before final filtering and bottling.

Beer is made from grains that must be processed prior to the fermentation process. Grains are sprouted to produce malt. Malt is then cooked to break down the grains into a mash producing simple sugars that are then easily fermented during the brewing process. Hops are added to the mash to impart the traditional beer flavor. Beer then undergoes a primary and secondary fermentation process. The beer is then aged with lagers being a darker and longer aged product. Carbonation is done by injecting CO₂ into the finished product prior to bottling. Hard liquor has a higher percentage of alcohol than either wine or beer. Since yeast is killed ( stopping further fermentation) once alcohol is between 12-15%, to obtain liquor with a higher percentage of alcohol (proof) distillation is a process used to remove water content essentially condensing the alcohol content in the final product.

It is interesting to understand that in addition to being a large part of beer, wine and liquor, ethyl alcohol is a solvent. It is widely used in industrial products including a fuel alternative to gasoline. Industrial grade ethyl alcohol (ethanol) has been treated (denatured) with additional compounds to give it a different color, odor, or taste.

Denatured alcohol would result in severe gastric distress and could prove toxic if consumed. With wine, beer, and liquor readily available, it is not likely that you would be tempted to drink industrial ethanol. All ethyl alcohol used in beverages or industrial solvents rely on the science of fermentation.

Additional References:

• Alcohol – This brief summary shares statistics on alcohol consumption and the measurement of alcohol percentage (proof) difference between beer, wine, and distilled spirits. All alcoholic beverages including beer contain ethyl alcohol.
• How to Brew Your First Beer – In this guide to brewing beer, you can follow the steps of the fermentation process to the completion of homemade beer. Included is a list of terms and ingredients to aid in your brewing adventures.
• The Process of Winemaking – After a brief introduction to the history of winemaking and the types of grapes used that contain a high sugar content, the author goes into detail explaining the differences in producing red wines, white wines, sparkling wines and fortified wines that have additional alcohol added during the fermentation process.
• Distillation of Alcohol (PDF) – Although this is a lab exercise in distilling alcohol from wine to produce a Brandy, it offers a look at the distillation process and an explanation in how the proof of an alcoholic product is determined. The chemical formulas for fermentation and illustrations for a distillation setup are included.
• Yeast – Yeast has the unique characteristic to ferment sugars. As such, it is widely used in the production of wines, beer, and other alcoholic beverages. This document gives information concerning the special strains of yeast, Saccharomyces carlsbergensis and Saccharomyces cerevisiae used during the brewing process.

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