大学四级-1101及答案解析.doc
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1、大学四级-1101 及答案解析(总分:712.00,做题时间:90 分钟)一、Part Writing(总题数:1,分数:106.00)1.1. 有些人愿意和父母居住在一起2. 有些人想自己独立居住3. 我的看法Styles of Living(分数:106.00)_二、Part Reading Compr(总题数:1,分数:70.00)How Ice Cream WorksThe U.S. ice cream industry sells about a million gallons of ice cream each year, dispensing cones, gallons, pi
2、nts, sundaes and other desserts through grocery stores and ice cream shops, In fact, eight percent of all the milk produced in the U.S. ends up in a frozen dairy product.Ice Cream or Frozen Dessert?Not just any frozen treat can be called ice cream. In fact, the U.S. Department of Agriculture has spe
3、cific rules that define what can and cant be labeled “ice cream“. To bear the “Meets USDA Ingredient Standard for Ice Cream“ stamp, it has to contain at least 10 percent milk fat, and a minimum of six percent non-fat milk solids. A gallon has to weigh at least 4.5 pounds.The range of milk fat (somet
4、imes referred to as butter fat) used in ice cream can go from the minimum 10 percent to a maximum of about 16 percent. Most premium ice creams use 14 percent milk fat. Higher fat content leads to better, richer taste and a creamier texture. Ice cream makers dont go higher than 16 percent because it
5、would be costly and very high in calories. An ice cream with this much milk fat would also taste so rich that people would probably eat it in smaller amounts, which would be bad news for people who sell ice cream for a living.Other frozen desserts, such as sorbets (果汁冰糕), low-fat ice cream, and froz
6、en yogurt, are not technically ice cream at all. Frozen custard is ice cream that has at least 1.4 percent egg yolk solids, and “soft serve“ can be any frozen milk-based dessert that has not gone through the hardening process-more on that later.In terms of specific ingredients, the recipe for ice cr
7、eam is simple. But in scientific terms, its complicated stuff. Ice cream is a colloid, a type of emulsion (乳状液). An emulsion is a combination of two substances that dont normally mix together. Instead, one of the substances is dispersed throughout the other. In ice cream, molecules of fat are suspen
8、ded in a water-sugar- ice structure along with air bubbles. The presence of air means that ice cream is also technically a foam.In addition to milk fat, non-fat milk solids, sugar, and air, ice cream also contains stabilizers and emulsifiers. Stabilizers help hold the air bubble structure together a
9、nd give the ice cream a better texture. Although gelatin(凝胶) was originally used as a stabilizer, xanthan gum, guar gum, and other compounds are used today. Emulsifiers keep the ice cream smooth and aid the distribution of the fat molecules throughout the colloid. Egg yolks were once used, but ice c
10、ream manufacturers now tend to use other chemical compounds. These stabilizers and emulsifiers make up a very small proportion (less than one percent) of the ice cream.Making Ice CreamWhether its being made in your kitchen with a hand crank, at a local homemade ice cream shop with a stand-alone ice
11、cream maker, or in a factory that cranks out thousands of gallons of ice cream every day, the process of making ice cream is basically the same. The only difference is the scale of the operation.First, you need ice cream mix. You can buy commercially made ice cream mix that is set to a certain milk
12、fat content. Ice cream factories usually make their own mix by combining milk, cream and sugar in a 3,000 gallon vat, with the proportions and mixing controlled by computers. The mix is then pasteurized ( 用巴氏法灭菌 ), or heated, to kill any harmful bacteria. If you were to make your own mix at home, yo
13、u could pasteurize it by cooking it in a double boiler, or use an egg substitute or pasteurized egg product. This step is important, because otherwise people who eat your homemade ice cream could get sick due to salmonella contamination. According to the Centers for Disease Control, those most at ri
14、sk include the elderly, very young children, and people with compromised immune systems.The next step in production is adding flavor to the mix. There are thousands of varieties of ice cream, so just about any combination of flavors is possible. From vanilla to cinnamon, chocolate to triple chocolat
15、e fudge brownie, it all gets blended into the ice cream mix. In a factory, this step takes place in vats that hold hundreds of gallons of ice cream, while giant steel paddles do the mixing. In your kitchen, a large bowl and a food mixer will work, or even a wooden spoon and muscle power if you want
16、some exercise. Solid chunks such as pieces of fruit, chocolate chunks, marshmallows, and candy are added later.The next step is where an ice cream making machine comes into play. The mix has to be simultaneously frozen and whipped. In a factory, this happens in a giant tube surrounded by pipes. The
17、pipes contain chemicals such as ammonia that freeze the tube, but the ammonia never comes into contact with the ice cream. The ice cream mix is pumped through the tube, where it gets cold very quickly. A dasher, or blade, turns inside the tube. This whips the mixture, introducing the air bubbles tha
18、t help give ice cream its structure. The dasher also serapes the sides of the tube, clearing off ice crystals that form there. This prevents large ice crystals from mining the flavor and texture of the ice cream. All the elements of this process are carefully monitored and controlled by computers. M
19、ost homemade ice cream shops use a batch freezer for this step, where the same process happens on a smaller scale.This step can be accomplished at home with a rock salt/ice mixture for freezing and a hand or electric cranked dasher to mix and scrape off the ice crystals.Once the ice cream has come o
20、ut of the ice cream maker, the process isnt finished. At this point, the mixture is frozen, but still soft Large chunks of candy and other goodies are now added. Then the ice cream is placed into containers. Factory machines pour it straight into cartons or buckets, or it can be extruded ( 挤压出 ) int
21、o shapes that have wooden sticks placed into them for individual treats.Now the ice cream needs to be reduced to a very low temperature, zero degrees Fahrenheit or below. Factories make it even colder since they need the ice cream to stay frozen while it is packaged and loaded onto trucks. It needs
22、to be very cold to freeze the ice cream quickly and prevent the formation of large ice crystals. This process is known as hardening. “Soft-serve“ is often simply ice cream that has not gone through this process.Well learn about the ice cream industry in the next section.Ice Cream IndustryIn 1999, re
23、tail sales of ice cream in the U.S., the worldwide leader in ice cream production, topped 4 billion. In 2002, more than 20 billion was spent on frozen desserts. The leading states in ice cream consumption are California, Indiana, Pennsylvania, Texas and New York. Americans ate an average of 21.5 qua
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