首页
登录
职称英语
The value of heat for the preservation of food has been known for thousands
The value of heat for the preservation of food has been known for thousands
游客
2023-10-15
12
管理
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 keeps 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. These germs include the bacteria which cause tuberculosis, undulant fever, typhoid and paratyphoid fevers, dysentery, diphtheri-a, scarlet fever and septic sore throat.
It has long been known to bacteria experts that the tubercle bacillus is the germ in milk which most strongly resists heat treatment. To destroy this organism it is necessary to heat milk to about 60℃ 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% 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 by law in 1923 as 63 -66℃ 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 °C , held in the tank for half an hour and then pumped out and cooled. This was a slow process and required a very cumbersome plant, so scientists worked for many years to produce a simpler, more convenient method, with less bulky 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℃ for at least 15 seconds, then, as it cools, the heat it loses is used, in part, to raise the temperature of the incoming milk in a device called a " heat-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, that is, they either do not sour milk at all, or sour it only slowly. Very strict cleanliness is, however, essential and all pipes, containers and bottling machines in a pasteurizing plant must be cleaned and sterilized daily. If the slightest trace of dirt remains all the benefits of pasteurization are wasted.
Questions 56 to 60: Mark each statement as either true(T)or false(F)according the passage. [br] In the H. T. S. T. system, the milk is kept in a holder tank at 72 ℃, for at least 15 seconds. ( )
选项
A、TRUE
B、FALSE
答案
B
解析
第四段第三句指出“In the H.T.S.T.system,the milk flows continuously through manysections of thin stainless steel pipes”,可知在高温瞬时法中,牛奶会不断流经不锈钢管道的多个部分,而非题干中提到的“被保存在容器里(is kept in a holder tank)”。
转载请注明原文地址:https://tihaiku.com/zcyy/3098894.html
相关试题推荐
Thevalueofheatforthepreservationoffoodhasbeenknownforthousands
Thevalueofheatforthepreservationoffoodhasbeenknownforthousands
Thevalueofheatforthepreservationoffoodhasbeenknownforthousands
Amassivedinosaurhatcherycontainingthousandsoffossilizedeggsanddoze
Amassivedinosaurhatcherycontainingthousandsoffossilizedeggsanddoze
[originaltext]Venezuela.Thousandsofoilworkershavegoneonstriketode
[originaltext]Venezuela.Thousandsofoilworkershavegoneonstriketode
[originaltext]Venezuela.Thousandsofoilworkershavegoneonstriketode
[originaltext]Venezuela.Thousandsofoilworkershavegoneonstriketode
[originaltext]Venezuela.Thousandsofoilworkershavegoneonstriketode
随机试题
中华民族的传统文化博大精深、源远流长。早在2000多年前,就产生了以孔孟(ConfuciusandMencius)为代表的儒家学说和以老庄为代表的道
LyricsandCriticalLiteracyIhaveorganizedmyexa
HowtoWriteaBookReviewI.ThedefinitionofabookreviewA.adescripti
Slaverywaslegalforover200yearsinsomepartsofNorthAmerica,particu
建筑起重机械备案是由建设主管部门根据规定,对产权单位的建筑起重机械进行登记编号,
关于无机结合料稳定材料击实试验方法,请回答以下问题。(2)无机结合料稳定材料击实
A.2 B.1 C.1/2 D.1/4
出其不意对于()相当于()对于回马枪A.
通过函证银行存款余额,注册会计师可以获取的审计证据包括()。A.银行存款是否存
A.地西泮 B.哌替啶 C.氯丙嗪 D.普鲁卡因 E.对乙酰氨基酚在物理
最新回复
(
0
)