Following carbonation, the beer is ready to be packaged. Perhaps the simplest form of packaging is to fill the beer directly into kegs. Kegs are constructed of aluminum or stainless steel and vary in size between 50 L and 100 L. Kegs not only mimic the traditional cask-style beers (in terms of perceived quality), but provide a convenient means of delivering non-bottled or canned product to the consumer.Thus,kegs are widely used by bars and restaurants for serving draught (otherwise known as draft) beer.
Beer destined for kegging is processed like other beers, in that it is clarified and filtered. Most kegged beer is filter sterilized, although some is heat pasteurized (see below). Therefore, its shelf-life is usually considerably longer than traditional casked beer (about three months versus one month). Kegged beer that is neither filter- or heat-pasteurized has a shelf-life similar to that of casked beer.
Importantly, since kegs are re-usable containers, breweries must pay particular attention to the keg cleaning and sanitizing operation before the kegs are re-filled.The interior of the keg, including the valve housing assembly where microorganisms may collect, is typically steam sterilized.And although it is outside the control of the brewer, the dispensing system used to pump beer from the keg to the glass is also a source of potential spoilage organisms.
The most common package for beer in the United States is the bottle or can (sometimes referred to as "small packs"). Bottles are usually constructed of glass, although plastic (e.g., polyethylene terephthalate or PET) bottles have become popular. Most cans are made from aluminum. Beer that is to be bottled or canned is pasteurized, either before or following packaging.
If the beer is pasteurized prior to filling, two options exist.The beer can be filter-sterilized, as described above, or it can be flash pasteurized via a plate-type, regenerative heat exchanger (similar to that used for pasteurization of milk). In fact, the time-temperature conditions for heat pasteurization of beer, 71°C to 75°C for fifteen to thirty seconds, are very near that used for milk. In beer, these conditions achieve a very high level of microbial killing (>5 logs), such that the product is stable at room temperature for at least six months.
Whether the beer is filter-sterilized or flash pasteurized, the packaging steps must be performed under rather stringent aseptic conditions to prevent post-processing contamination. Bottles (whether glass or plastic) and filling and capping (i.e., crowning) equipment must be sterile, and surroundings protected such that microorganisms are excluded. Sterile N2 or CO2 can be used to flush the environ ment, and sterile water used to ensure that the relevant equipment, especially the areas around the fillers, remain free of microbial contami-nants.The beer filling and packaging operation is essentially no different from that used for milk, juice, or other fluid products.
Beer can also be heat pasteurized after it has been filled into cans or bottles. In fact, most beer consumed in the United States is processed via tunnel pasteurization systems in which filled and sealed bottles or cans are heated by hot water. Tunnel pasteurizers operate in a continuous mode, with the temperature being gradually raised to as high as 62°C and held for up to twenty minutes.The collective effect of longer heating at lower temperature has the same kinetic effect on the destruction of microorganisms in beer as flash-pasteurization.
Pasteurizing the beer after it is already in the sealed package prevents post-pasteurization contamination; however, the longer exposure to heat may promote undesirable flavor changes in the beer, including formation of cooked and oxidized flavors. Of course, some beer manufacturers eschew any type of heat treatment and instead rely on filtration systems for preservation of beer. However, even filtration is not benign, as flavor and other beer constituents may be removed during the filtering process.Thus, the challenge for modern brewers is to produce not only a beer with desirable flavor, body, and appearance characteristics, but also one that meets the preservation requirements necessary to operate successfully in a highly competitive market.
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