Friday, February 8, 2008

Measuring the number of calories

Nutrition scientists measure the number of calories in food by actually burning the food in a bomb calorimeter, which is a box with two chambers, one inside the other. The researchers weigh a sample of the food, put the sample on a dish, and put the dish into the inner chamber of the calorimeter. They fill the inner chamber with oxygen and then seal it so the oxygen can’t escape.
The outer chamber is filled with a measured amount of cold water, and the oxygen in the first chamber (inside the chamber with the water) is ignited with an electric spark. When the food burns, an observer records the rise in the temperature of the water in the outer chamber. If the temperature of the water goes up 1 degree per kilogram, the food has 1 calorie; 2 degrees, 2 calories; and 235 degrees, 235 calories — or one 8-ounce chocolate malt!

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