Drying Milk

The Italian explorer Marco Polo reported that the soldiers of Kublai Khan (the Emperor of the Mongols in the 13th century) knew how to make milk powder. They would leave milk to dry in the hot sun of the Gobi desert till it became quite thick. When they needed milk, they would put some of the dry paste in water and dissolve it. Easy wasn't it?

Nowadays, milk is dried quickly in factories. There are two ways. One is called 'spray drying'. Milk is sprayed into a huge chamber, and heated air is blown from the other end. The droplets of the milk dry up very quickly in the hot air, and fall down. The powder can then be scraped off and packed into jars or sachets.

Another way is 'drum drying'. In this, milk is sprayed onto huge drums, which are heated by electric current. The heat makes the water in the milk evaporate, and the powder stays behind on the drum. Drum-dried milk is often flaky and sticky, while spray dried milk is powdery and non-stick.

Buy a few sachets of milk powder of different brands. Ask your friends to join you in feeling and tasting the powder. Which brand was spray-dried and which was drum-dried?

Why dry milk (and anything)

All living things need water to survive. This is because water is the solvent in which most chemicals dissolve - like vitamins, amino acids, carbohydrates and minerals. The enzymes that convert the food we eat into energy work only in a wet environment. This is true for every living organism, including bacteria.

If you go to a village, you will see chillies, papads, fish, grapes (to make raisins) and other things left out to dry in the sun. In a dry environment, bacteria cannot grow and multiply. If you remove moisture from food and store it in water-tight and air-tight containers, it will last almost forever.

The Colombo Plan

In the 1950s, there were food shortages in many countries, including India. A group of 8 countries had a meeting in Colombo, Sri Lanka. Here they created a plan by which countries like Australia, New Zealand and Canada would supply milk and other food to countries which were short of them. Under this plan, a large amount of milk powder was shipped from New Zealand to India. The powder would be dissolved in water to make milk, which was then distributed to homes. This continued till the White Revolution, when India was able to overcome its shortages.