Food Microbiology
Alcohol
Wine
Egyptian records dating from 2500 BC refer to the use of grapes for wine making, and numerous Old Testament references to wine indicate the early origin and significance of the industry in the Middle East. Undoubtedly wine continues to play a significant role in society today.
Wine is a beverage made from fermenting grape juice. The many varieties and flavors of wine come from the extensive selection of possible grapes to be fermented and from the vast array of yeasts and bacteria that may be used. The alcohol content of most wines ranges from 10% to about 14% by volume.
The first step in making wine is to allow the grapes to ripen in the vineyard so that they contain and adequate amount of sugar and acid. Next the grapes should be fermented by the selected yeast to produce the appropriate flavor and odor. This step must be monitored carefully so that unwanted yeasts to not overpopulate the juice. The most common yeasts for fermenting wine are in the family Saccharomyces, although wild yeasts such as Pichia, Kloeckera, and Torulopsis may be used. Technicians in the science of making wine, known as enologists, generally do not agree on the best yeast for fermenting wine, however S. cerevisiae is most commonly used. The wine is fermented at an average temperature of 25 degrees Celsius for most strains of Saccharomyces. After the yeast fermentation is completed, a second fermentation by lactic acid bacteria to convert the malic acid into lactic acid and CO2. In this fermentation step, many unkown metabolic by-products are produced which give each wine its characteristic taste. Finaly, the wine is filtered and bottled.
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Beer
Beer is an alcoholic beverage made from malted barley, water , hops and yeast. Some beers contain a variety of other adjuncts, cereals that are not malted, but most do not.
As early as 6,000 years ago the Sumerians were brewing beer. In those times beer was cloudy and unfiltered. "Drinking straws" were often used to avoid sucking down some of the extremely bitter brewing residue as a result of fermentation. Today there are literally thousands of beers ranging from mass produced commercial drinks to colorful and flavorful microbrews. The alcohol content of most beers ranges from about 3% to 11% by volume.
In making beer, the first step is to malt the
grains. This gets them ready for fermentation. It begins with keeping barley
in water until it begins to germinate. Germination is
usually halted prematurely by allowing the grain to dry, either naturally,
or in a kiln. Hops may be added at a variety of different times depending
on the desired taste. The earlier the hops are added, the more bitter the
beer. The mixture is then heated for several hours. As the hot water soaks
into the malt, its fermentable sugars are released. The mixture is then cooled
to a temperature suitable for fermentation. Yeast is now added and the beer
is soon on its way to being complete. Fermentation can take anywhere from
a few days to several weeks depending on the type of beer desired.
For more information on beer brewing, check
out: http://www.beerchina.com/beerenglish/beerknow01_en.htm