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  3. The value of heat for the preservation of food has been known for thousands of years, but it was not realized until the nineteen

The value of heat for the preservation of food has been known for thousands of years, but it was not realized until the nineteen

admin2012-01-05  54
问题    The value of heat for the preservation of food has been known for thousands of years, but it was not realized until the nineteenth century that a very mild heat treatment far below the boiling point, made liquid foods such as milk keep much longer. The discovery followed the work of the French scientist Louis Pasteur on wine and beer.
   The process, called after him "pasteurization", is a carefully controlled mild heat treatment. It was found that the process served two purposes, it prevented the souring of milk, and it destroyed the dangerous disease germs which sometimes occur in this product.
   It has long been known to bacteria experts that the tubercle bacillus is the germ in milk which host strongly resists heat treatment. To destroy this organism it is necessary to heat milk to about 60 degrees centigrade for 15 minutes, and its destruction has always been taken as a way of testing the efficiency of pasteurization. A heat treatment of this kind destroys about 99 percent of the common bacteria in milk, including nearly all those which cause milk to turn sour.
   To ensure the certain destruction of tuberculosis and other disease germs in milk, it must be held at a fixed temperature for a fixed time. In Britain, for example, these conditions were defined-coy law in 1923 as 63-66 degrees centigrade for 30 minutes. This became known as the "holder" process, since the raw milk had to be pumped into a large tank, heated to just over 63 degrees centigrade, held in the tank for half an hour and then pumped out and cooled. This was a slow process and required a very large plant, so scientists worked for many years to produce a simpler, more convenient method, with less large equipment.
   The latest method, officially approved in Britain in 1949, is known as the high-temperature-short-time, or H. T. S. T. method. It has now almost entirely replaced the "holder" process. In the H. T. S. T. system, the milk flows continuously through many sections of thin stainless steel pipes, During the process, the milk is held at 72 degrees centigrade for at least 15 seconds then, as it-cools, the heat is used, in part, to raise the temperature of the incoming milk in a device called a "wheat exchanger".
   Efficient pasteurization may reduce the bacteria in raw milk from, say, one million to only a few thousand per cubic centimeter. The bacteria left are chemically mostly of the inert type, thatis, they either do not.
Which of the following statements is NOT true according to the passage?
选项 A、Pasteurization process is named after a French scientist.
B、Tubercle bacillus accounts for the largest number among all germs in milk.
C、Heating temperature may vary according to different processing methods.
D、Neither of the pasteurization methods mentioned in the passage can 100% reduce bacteria in raw milk.
答案B
解析 本题考察文章细节。第一段介绍，巴氏杀菌法是根据French scientist Louis Pasteur命名的。各种杀菌法对温度的要求从60，63到72 degrees各不相同。杀菌效率可达到 99 percent或one million to only a few thousand per cubic centimeter，但都不能达到100%。对于tubercle bacillus是不是牛奶中数量最多的细菌，文章并未介绍。
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