第2章 Lesson 2 Lyophilization

Lyophilization is the scientific name for freeze drying — which is very useful for preserving perishable foods in addition to making them lighter and easier to transport. One of the first foods to be freeze dried was ice cream. This tasty treat was originally made for astronauts. However, freeze drying is much more than just a novelty. Hikers often carry freeze dried food because of its light weight. it is also used to manufacture instant coffee and some pharmaceuticals.

The basic idea behind freeze drying is to remove every bit of moisture from a substance. Because the water content in freeze dried food is so greatly reduced, it is much less likely to spoil due to microorganisms and enzymes. In fact, if they are sealed properly, freeze dried foods can remain unspoiled at room temperature for many years. Freeze drying also allows food to retain its flavour and smell.

When food is preserved by basic dehydration, it is simply placed somewhere hot and arid and the water evaporates — but not all the water. This method only removes 90 to 95% of the water, which can slow down spoilage, but not completely prevent it. Freeze drying, on the other hand, is more complex. The material is first frozen. After that the surrounding pressure is reduced so that the frozen material can transform from solid into gas. This is known as sublimation, and is the same process that accounts for the disappearance of snow in the winter, even when the temperature has not risen high enough for the snow to melt. Freeze drying can take several days because rushing the process can change its structure and composition. One of the objectives of freeze drying is to leave these things intact.

I. Word List

perishable: easily spoiled, goes rotten quickly

astronauts: space travellers

pharmaceuticals: legal drugs

arid: dry

objectives: goals

II. Fill in the blanks—Find the important information in the reading.

1. Freeze dried ice cream was first eaten by _ _ _ _ _ _ _ _ _ _.

2. Freeze drying retains the flavour and _ _ _ _ _ of food.

3. In basic dehydration, food is not _ _ _ _ _ _.

4. Freeze dried food does not _ _ _ _ _ quickly.

5. Freeze drying is more _ _ _ _ _ _ _ than simple dehydrating.

III. Answer the following questions.

1. What are some products that are commonly freeze dried?

___________________________________________________________.

2. What kind of people often carry freeze dried food?

___________________________________________________________.

3. What are some advantages of freeze dried food?

___________________________________________________________.

4. Do you like freeze dried food? Why or why not?

___________________________________________________________.

5. Can you think of any possible disadvantages of freeze dried food?

___________________________________________________________.

IV. True or False—Read these sentences carefully. Write T (true) or F (false) for each one.

___ 1. Lyophilization and freeze drying are the same thing.

___ 2. Freeze drying increases the weight of food.

___ 3. Water can not be added to freeze dried food.

___ 4. Lyophilization is mostly just a novelty.

___ 5. Lyophilization changes the structure of food.