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The Science of Home Brewing Beer and Wine

Updated by Jim Deckebach
home brewing beer

Although science might not be your main focus as you enjoy an adult beverage, once you understand some of the chemical changes that happen in the process of creating wine or beer, you might find that you enjoy these drinks even more. Science is the driving force behind the flavor development of beer. It's also responsible for the full-bodied taste of wine.

The Science of Making Beer

Beer Ingredients

Beer contains water, yeast, malted grains, and hops. These ingredients in various combinations will contribute to the final product. The flowers from hop plants are what give beer a lot of its flavor. Hop plants are also used in herbal medicines.

Water Quality

The mineral content of the water used to brew beer will have a major impact on the final product. Hard water contains high levels of calcium and magnesium, which affect how yeast grows and metabolizes sugars in the beer. If the water contains bicarbonate, the pH level will also be affected as the beer ferments.

Roasting Grains

Those who want to create beer with a toasted or caramelized flavor should roast the grains for a longer period prior to brewing. Dark-roasted grains have higher levels of degraded glucose molecules, which leads to darker beer.

Hops

Hops serve as the surfactant that helps trap bubbles in beer heads. Without hops, beer would have no head, and it would have a bitter taste. Hops add flavor to beer as well as providing important stabilization that enables the palate to sense the different flavor notes.

Fermentation

Yeast is the key ingredient that makes beer both alcoholic and carbonated. The grains and hops include glucose molecules, and yeast cells convert glucose to ethanol and carbon dioxide. The type of yeast used to brew beer will determine the final fermentation process. Ale yeasts result in the most fermentation. Lager yeasts ferment at lower temperatures, which creates a crisp flavor. Although used less often, wild yeast results in an acidic brew. The type of yeast used will contribute to the carbonation level, the type of esters, the amount of alcohol, and the final flavor.

Factors That Influence Flavor and Fermentation

The mineral content of the water, temperature, aeration, length of fermentation, and pitch rate of the yeast work together to help determine the flavor of the final brew, and all of these variables can be adjusted or controlled by the brewer. The flavor can also be influenced by esters that build up during fermentation. The most common ester is ethyl acetate, but isoamyl acetate is another common ester.

The Science of Making Wine

Primary Fermentation

Starting with fresh-picked fruit, including stems, crush the fruit. Add wine yeast, and wait for the mixture to begin fermenting. Monitor the acidity level and make adjustments as needed. After completing this phase, separate the solids from the liquid by pressing, draining, or siphoning off the liquid. Pressing results in a higher yield. After separating the liquid from the solids, there's not much to do but watch for any issues with the fermentation process, which will usually make themselves known with unusual odors.

Racking

After this stage of fermentation is done, "rack" the wine by siphoning the liquid from the sediment on the bottom of the container. Racking might be done two or three times with a couple of months between each.

Adding Sulfur Dioxide

After fermentation, add sulfur dioxide to preserve the wine, if you wish. If you prefer to minimize the chemical content of your wine, use potassium metabisulfite. The recommended measurement is 25 to 45 parts per million, or a quarter-teaspoon of potassium metabisulfite for each five gallons of wine.

Bottling

Fermentation can take up to four weeks, and the wine will be finished after fermentation completes. However, for a more complex flavor, you may opt to age the wine at least six months before bottling it. Just before bottling, sweeten the wine if you wish. Then, bottle the wine, making sure to use a variety of smaller containers that can be sealed completely full. Keeping it all in one container raises the risk that it will spoil, as any empty space left in the container can contribute to oxidation. A wine bottle should be completely full or empty for best results.

Cleaning and Sterilizing

Be sure to use completely sterile equipment to bottle your wine. Use potassium metabisulfite dissolved in water to disinfect the bottles before filling them. You can also use citric acid in water to make the water acidic, enhancing the effectiveness of the potassium metabisulfite.

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