Реферат: Brewing Beer Essay Research Paper BREWING BEER
Brewing Beer Essay, Research Paper
People have been enjoying beer for centuries. Brewing beer started about 6000 years ago in ancient Mesopotamia. Back then, people brewed beer and baked bread similarly. These days, beer brewing has become a science.
Brewing beer is a complex biochemical process, part of which is fermentation. Fermentation of sugars and grains into ethyl alcohol is among the oldest known chemical processes used by man. There are four major ingredients used in brewing beer; water, malted barley, hops, and yeast. Sugar for the fermentation process is provided by the breakdown of starches in the hops and malted barley. Upon action by the enzymes present in the malted grains, the long chain starch molecules are broken down into simpler sugars which are fermentable and give beer its alcohol content. Longer chain sugars, called polysaccharides, are also formed. These sugars primarily give beer its body and sweetness.
The process begins with the preparation of the malted barley. Malted barley is a barley that has been allowed to germinate to a degree. Before the plant begins to rely on chlorophyll, the barley is dried and the rootlets are removed from the partially germinated seeds. During germination, the seed produces diastase enzymes that can convert starch into usable sugars. Trace elements necessary for the life cycle of yeast, such as Zinc and Calcium are also found in malted barley.
The malted barely is crushed to a suitable size for brewing, usually by using rollers. The purpose of this is to make the pieces small enough for the hot water to extract their flavor when it is added to make the wort. The wort is the mash, or mixture of assorted grains and water, that goes into the beer after it has been added to hot water and started to boil. Over grinding can make the barley very difficult to get out of the wort. Grinding or cracking the barley causes trace amounts of barley to enter the air and the process needs to be isolated from the vats used for fermentation.
The malted barley is mixed in appropriate proportions with hot water to begin preparation of the wort. Beer is made up of 90%-95% water.
The chemistry of the water used can effect both the flavor and the brewing efficiency of the beer. Excessive chlorine can greatly effect the other ingredients in the beer and can result in a harsh aroma and flavor. Boiling or filtration is often used to remove unwanted chlorine. The water used is usually hard. Hard water is water with a high content of minerals. A soft water can result in a milder flavor and aroma. Water hardeners such as table salt (NaCL) and gypsum (CaSO4) are sometimes added to soft water. Bacteria from the water can spoil the wort. This is usually removed through boiling.
The mixture of crushed malted barley and water is called the mash. The mash is put into a boiler and brought to a boil for around thirty minutes. The enzymes in the malted barley are reactivated by hydration and starch-to-sugar convergence is continued from germination.
The starch in the barley contains roughly 20% amylose and 80% amylopectin starches, which are very similar, but differ in molecular size and shape. Each contains up to a million glucose molecules tied together in a long chain creating a single starch molecule. Upon action by the enzymes present in the malted grains, malted barley and hops, diastase and amylase (also known as alpha amylase and beta amylase), the long chain starch molecules are broken down into simpler sugars, such as maltose (C12H22O11), glucose (C6H12O6), and maltobiose. These sugars are fermentable and give beer its alcohol content. Longer chain sugars, called polysaccharides, are also formed. These sugars primarily give beer its body and sweetness.
The grains are now extracted from the liquid. The end transparent liquid is a complex solution of sugars. Hops are now added to the boil. Hops are the cones or flowers of the female hop vine. The cones contain a resin called alpha acid that gives beer its bitterness flavor. Hops help to inhibit bacteria in beer, maintain flavor stability, and to retain the head of the beer. There are two main types of hops. Noble hops are low in bitterness and have a pleasant aroma and flavor. High-alpha hops have high bitterness but a less pleasant aroma. Today, the bitterness for each type of hops is rated by alpha acid units(AAU). It is calculated by the alpha acid percentage in the hops multiplied by the weight of the hops in ounces.
Continued boiling is necessary to extracts the hops’ bittering qualities. During this time the bittering resins dissolve into the mixture. Unwanted proteins coagulate and precipitate out the from the wort. The wort is now cooled and moved to fermenters.
Fermentation is the all important step of brewing. The initial stage of fermentation is an aerobic process, therefore it utilizes the free oxygen in the mixture. Yeasts derive energy from oxygen during its respiration stage. Oxygen is most important at this initial stage of the brewing process called the yeast’s respiration stage. If oxygen is not present during respiration, fermentation will not continue. The correct amount and type of yeast is added to the wort. During fermentation, yeast goes through its life cycle from beginning to end. It is in this stage that the beer gets its alcohol content and its flavor.
Yeast is a single-celled organism belonging to the fungus family. There are thousands of strains of yeast, but there are only two main types used for beer. These types are ale yeast and lager yeast. Most commercial beers add specific strains of yeast, but early brewers did not. They let the beer sit so that the yeast in the air would enter it. Today, Lambic brewers still use this process. Ale yeasts are sometimes called “top-fermenting” (Saccharomyces cerevisiae) yeasts. This is because they tend to flocculate at the surface of the beer in the beginning of the fermentation process. Ale yeasts prosper in the temperature rang of 55 – 75 degrees F. This type of yeast is used to make ales and stouts. Lager yeasts are sometimes called “bottom-fermenting” (Saccharomyces varum) yeasts. These yeasts tend to flocculate at the surface of the beer and then sink to the bottom of the fermenters. A temperature range of 32 – 55 degrees F is best for lager yeasts. This type of yeast is used to make lagers and steam beers. There are several conditions that must be kept constant if the yeast is to go through its life cycle properly. Temperatures should also be kept fairly steady. Yeasts don’t like sudden changes in temperature. If the environment that the yeasts in is to cold, their activity will slow down or stop completely. If the temperature is to high, it could kill the yeasts. Different liquid environments exert different pressures. The cell walls of the yeasts are delicate and require gradual transitions. Sudden changes in osmotic pressure could cause the yeasts to implode, explode, or go into shock. Osmotic pressure is the pressure that the liquid applies on the yeast cells. Most beer yeasts prosper in a pH of 5.0 to 5.5. However, this acidic environment should occur without any adjustments.
Throughout fermentation, yeast is going through its life cycle. The first stage is respiration. Yeasts are added to the wort and start to grow in the presence of oxygen. During this period, yeasts gain and store energy for use in reproduction and other activities. Yeasts gain energy from oxygen and sugars. Next, the yeast undergoes reproduction. Yeast reproduces through budding. The third phase is fermentation. When the oxygen is depleted, the yeasts go into anaerobic fermentation. During this phase, yeast loses energy by converting sugars to alcohol, carbon dioxide, and distinct flavor. At this time, yeast is dispersed and in a state of suspension in order to obtain maximum contact with the liquid beer mixture. The final stage is sedimentation. At this stage the yeast runs out of food and energy. It gathers and then seperates by settling to the bottom or floating to the top, essentially stopping all activities.
Within the first 24 hours in the fermentation vat, foam, called kraeusen, will be produced. This is the result of the yeast’s vigorous attack on the sugar. The yeast begins to multiply rapidly. Through the enzymatic action of the yeasts, it consumes the sugars and converts them into ethyl alcohol (C2H5OH) and carbon dioxide (CO2), which then carbonates the beer. In addition to ethyl alcohol and carbon dioxide, there is an estimated 2000 other by-products that make-up the distinct aromas and flavors of beer. These by-products are various esters, aldehydes, polyphenals, and higher alcohols. The pH of the wort now drops naturally from about 5.2 to the range of 4.0-4.3. This pH is crucial for keeping bacteria to a minimum and it aids in the flocculation of the yeast. The total time it takes for fermentation to complete is almost a week. During that time, the level of alcohol reaches a certain equilibrium, the fermentation process slows, the yeasts flocculate even more, the foam will diminish as the yeast depletes the sugar supply, and the newly fermented beer is cooled and transferred to conditioning tanks for aging.
Before storing, filtration or pasteurization is usually applied. Pasteurization is a method of preserving food. It involves heating the food to burn out all the bacteria. This will stop the food or drink from spoiling. If the pressure in the filter is to high during filtration, it will cause the filtration column to explode. High pressure can result from a cake of yeast on the trays not letting the beer pass. This can be prevented by adding diatomaceous earth to the brew to keep the pressure low. Diatomaceous earth is an algae that has a hollow structure similar to a skeleton. These hollow bodies allow the beer to continue past the cake.
There are hundreds of different types of beer, each one different from all the others. Special flavors can be achieved by what type of yeast is used and the AAU of the hops. Also, malts, such as caramel malt and chocolate malt, can be added to the beer for flavor. Lager beer, which is the most popular beer in the United States, is noted for its effervescence and golden color and has several different variations. Light beer is lager beer that has been specially brewed to reduce carbohydrates and calories. Pilsner beer is a lager that has a stronger hops flavor than regular lager. Dry beer is a lager that doesn’t taste as sweet as regular lager. Malt liquor is a lager with a higher alcohol content. Another popular category of beer is ale, which has a distinctive hop flavor and aroma. Finally there are dark beers. The three main types of dark beers are bock beer, porter, and stout.
One beer that is particularly unique is Lambic beer. Lambic beer is a very ancient beer style. Unblended Lambic beer has a rich flavor, quite different from other beers available today. It lacks some of the carbon dioxide and has a more sour flavor than today’s beers. Today, this sherry-like beer can only be tasted in a few pubs in and around Brussels. The wort in Lambic beer is composed of 60% malted barley and 40% unmalted grains. Lambic beer’s fermentation is wild, like its ancient predecessor. No yeast is artificially added to the wort. The wort is left open to the open air of the “Zennevali”. This causes wild yeast cells like Bretanomyces Bruxellensis and B. Lambicus which are always in the environment in Brussels to enter the wort and start a natural and spontaneous fermentation. Also, Lambic brewers use old dry hop, because they do not want the bittering quality but the preservative quality of the hops to enter the beer. Finally, Lambic brewers use wheat as their un malted grain. Lager brewers use young hop and uses corn or rice instead of wheat as the unmalted grain.
Brewing beer is a very complex chemical reaction, and has come a long way from when people first started to brew beer in their back yards. Around the world, people drink twenty-two billion gallons of beer a year. In the United States of America, people drink about twenty-four gallons a year. Now people add special ingredients to their brew to get certain flavors, beer brewing is studied to try and find ways to get rich flavors, and millions of people around the world are employed in the beer industry.
De Heersmaecker, Jacques. “The Mystery of Lambic Beer.” Scientific American,
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