Rick White, age 12, of Tulsa, Okla., for his question:
What makes the holes in Swiss cheese?
These holes are caused by a strain of bacteria called Propionibacterium either Propinionibacterium helvetium or Propionibacterium shermanii. These fancy names, believe it or not, belong to tiny plants too small for our eyes to see. Although there are giants and midgets among the countless varieties of bacterium which share our world, on the average they measure about 25,000 to an inch.
They are in the soil in countless numbers, in the water, on every surface we touch and even adrift in the air. Spores, or seedlets of bacteria, float everywhere. True, a few bacteria are dangerous to us because they cause disease. But a few are so useful to us that we could not survive without them. Some help to purify our water supplies, some cause things to decay and there are bacteria in your body without which you could not make proper use of your food.
Cheese can be made only with the help of bacteria. And certain strains of bacteria thrive best and often only in certain places. Our friend the Propinionibacterium was a native of Switzerland for countless ages.
It thrived in the soil and the pastures. The bacteria and their spores were in the milking pails, on the skin of the milkmaids and the cows and, of course in the milk. Cheese is made from milk. The Swiss learned to make cheese long before anyone knew that bacteria always helped to do this work, but Swiss cheese could be made only in Switzerland.
Cheese is made in two stakes. The milk is curdled: Then the solid curd is dipped out and allowed to ripen. Certain bacteria may cause the milk to curdle and others will do the ripening fob. Actually, this is done when the bacteria digest the milk solids. In the digesting certain materials in the milk solids are turned to gas which collects in big bubbles inside the ripening cheese.
When our Swiss bacteria were identified, it was possible to prepare them in pure form. Nowadays, any dairyman can make Swiss cheese wherever he lives. He simply adds a little Propinionibacterium culture to his brew and the tiny bacteria ripen the cheese and put the holes in it.