Pasteurization, creaming and homogenization

When raw milk is left standing for a while, it turns "sour". This is the result of fermentation. Pasteurization is used to kill harmful micro-organisms by heating the milk for a short time and then cooling it for storage and transportation. The process is called after French scientist Pasteur. It’s a carefully controlled mild heat treatment.

Milk is rendered free of pathogenic bacteria by pasteurization. Milk is heated to a specified temperature for a specified time. Pasteurization on a batch operation requires a jacketed vat where steam or hot water can circulate and heat the milk. This treatment requires the longer times at lower temperatures to accomplish pasteurization. Modern methods of pasteurizing milk and milk products utilize the high temperature short-time pasteurizer. In Europe and the United States milk may be ultra-heat-treated.

Pasteurization of cow milk initially destroys any potential pathogens and increases the shelf-life. Pasteurized milk must be stored cold by both suppliers and consumers. Dairies print expiration dates on each container, after which stores will remove any unsold milk from their shelves. In many countries it is illegal to sell milk that is not pasteurized.

Upon standing for 12 to 24 hours, fresh milk has a tendency to separate into a high-fat cream layer on top of a larger, low-fat milk layer. The cream is often sold as a separate product with its own uses. The fat globules rise to the top of a container of milk because fat is less dense than water.

Milk is often homogenized, a treatment which prevents a cream layer from separating out of the milk. The milk is pumped at high pressures through very narrow tubes, breaking up the fat globules through turbulence. Homogenized milk tastes blander but feels creamier in the mouth than unhomogenized. Homogenized milk may be more digestible than unhomogenized milk

Practice 1. Re-read the text and answer the questions:

1. Why do people pasteurize milk?

2. How must milk be stored?

3. Why does high-fat cream layer separate from milk layer?

4. What are the reasons to homogenize fresh milk?

Practice 2. Give the Russian equivalents to the word-combinations from the text:

-raw milk

-harmful micro-organisms

-for a short time

-the process is called after

-mild heat treatment.

-specified time

-jacketed vat

-modern methods

-ultra-heat-treated

-increases the shelf-life

-expiration dates

-unsold milk

-high-fat cream layer

-low-fat milk layer

-through turbulence

-at high pressures

Practice 3. Match up the words on the left with the definitions on the right:

1. to pasteurize 2. cream 3. globule 4. to rise 5. vat 6. container 7. circulate 8. harmful

a. a large container used for mixing or storing liquid substances, especially in a factory b. a small ball of something, especially a drop of liquid c. to heat something at a controlled temperature for a fixed period of time in order to kill bacteria d. to move around or through something e. causing something bad f. to increase in number, amount, or value g. the thick yellowish-white liquid that forms on the top of milk h. a hollow object, such as a box or a bottle, which can be used for holding something

Practice 4. Complete the sentences using the words from the table:

souring shelf-life vat homogenization heated pasteurization dense bacteria

1. The process of _______ serves two purposes: it prevents the ________ of milk and kills harmful ________.

2. Ultra-pasteurized products have extended _________.

3. _______ is a process of averting of milk layering.

4. Milk is ______ for 30 min when pasteurized in a _____.

5. A cream layer separates out of the milk because fat is less ________ than water.

Practice 5. Complete the table: