Beer Fermentation Process
The glucose-supplying ingredient in beer is typically barley, although corn, wheat and rice can be used as filler or flavoring. The glucose molecules in these grains are stored in long molecular chains called "polysaccharides" or "starches." To break the starches down into glucose, the grains are pulverized into a fine powder, mixed with water and finally boiled for a few hours. The presence of water at these high temperatures draws the polysaccharides out of the grains and into solution (a process known a "steeping"). After the polysaccharides are in solution, special enzymes added to the mixture break them down into monosaccharides (i.e., glucose). The final glucose-rich mixture known as the "wort." Note: during this process, oil from hops seeds are added to mixture, both for flavor and to protect yeast from competitive bacteria during fermentation.
Once the wort is ready, it is cooled and poured through several filters (to remove solids and bacteria) into a special air-tight, pressurized tank. Here, yeast is added to the wort to begin converting the glucose to alcohol. Depending on whether the brewer wants the final beer to be a lager or an ale, he will add a specific type of yeast to the wort and heat the tank to a certain temperature. Generally, lagers use "Saccharomyces pastorianus" yeast and use a fermenting temperature between 68 and 82 degrees F. They are less fruity and spicy than ales but feature a stronger hops flavor. Ales, on the other hand, use "Saccharomyces cerevisiael" yeast and a temperature between 68 and 104 degrees F.
Inside the fermenting tank, the lack of oxygen forces the yeast to forgo aerobic respiration (i.e., using oxygen to convert glucose into energy) and switch to fermentation (i.e., converting glucose into alcohol and carbon dioxide to derive chemical energy). As the yeast consumes the glucose for fermentation, the pressure inside the tank increases greatly due to the buildup of carbon dioxide. To prevent an explosion, a special, one-way valve in the chamber to relieve pressure periodically.
After anywhere from one to three weeks, the yeast will have produced the desired concentration of alcohol in the wort, making it ready for bottling.
Spirits Fermentation Process
The process for fermenting spirits (e.g., vodka, gin, rum, whiskey, tequila) is very similar to beer brewing, minus the barley and hops. Depending on the spirit, the brewer will start by mashing a starch and mixing it with water and polysaccharide-attacking enzymes. For example, vodka uses potatoes, gin uses corn, rum uses sugarcane, tequila uses agave and whiskey uses cereal grains.
The water-starch-enzyme mixture is then heated and agitated with automatic mixers to break the polysaccharides down into glucose. The mixture is then boiled to kill microorganisms. Once inoculated, the mixture is poured into a sealed metal chamber where yeast (Saccharomyces cerevisiael) is added to it.
After heating the chamber to a temperature between 68 and 104 degrees F, the yeast is left with the glucose-rich mixture for 48 to 96 hours. During this time, the yeast switches to fermentation for energy, converting the available glucose into alcohol.
Once complete, the alcohol-containing mixture is poured into a distillery. By heating the liquid to 174 degrees F (i.e., the boiling point of ethanol), the alcohol evaporates out of solution. The distillation equipment then captures the alcohol vapor and condenses it into a more concentrated form. This distilled alcohol is the flavored or "aged" in special oak barrels to give it a distinctive taste/aroma.
Wine Fermentation Process
Unlike beer and spirits, wine uses a significantly different technique for fermenting glucose. First, wine uses the glucose naturally occurring in mashed grapes to as fuel for fermentation. After being mashed, the mixture of juice, seeds, skin and vine is allowed to sit for a period between two hours and three weeks known as "maceration."
Next, the solids are separated from the juice, either through centrifuge or a bladder-pump mechanism. The juice is then mixed with one of several species of yeast (typically Sacchromyces ellipsoidues), depending on the desired final product. Here, the juice (a.k.a. the "must") is poured into a sealed, heated vat where the yeast ferments the glucose from the grape juice over the course of three weeks.
Historically, however, the must would be added to an oak barrel and allowed to ferment at lower temperatures. This took longer (approximately six weeks) but added flavor and aroma absorbed from the barrel. For this reason, many high-end wines still use barrel fermentation today.
Once fermentation is complete, the winemaker will often add sulfites/sulfur dioxide to the wine in order to disinfect it from acetic bacteria and other microorganisms that can spoil the taste over time.
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