Calories measure energy and can be used to describe any fuel, from petrol to bread. One calorie is the amount of energy required to raise the temperature of one gram (0.035 ounces) of water by one degree Celsius (1.8 degrees Fahrenheit).

Food labels often quote energy content in kilocalories (kcal), because food is so rich in energy that it makes more sense to label 1,000 calories at a time. The number of calories in any given item of food is calculated by measuring how much energy is released when a substance is burned.

Inside our bodies, molecular machinery is responsible for burning the fuel we eat, but in the lab, using a spark gives the same result. The traditional method of calorie calculation is to put the food inside a sealed unit known as a bomb calorimeter.

The food is surrounded by an atmosphere of oxygen to ensure it will burn well, and the container is sealed and surrounded by a known volume of water. A spark ignites the food inside and allows it to burn until it is reduced to charcoal, releasing all of the energy contained inside.

The energy is converted to heat, which in turn raises the temperature of the water. By measuring the water’s temperature change, you can then find out exactly how much energy has been released and calculate the calories from there.

Today, many food manufacturers use a different system to create nutritional labels; instead of burning the food item whole, they simply add up the calories of the different components, such as fats, carbohydrates and proteins.

Calculating Calories:-

1. Setting up the calorimeter The first step in measuring the calorie content of our food is to place the item inside a bomb calorimeter. The
food is then sealed in a container that’s is filled with flammable oxygen gas, and is placed inside a second container containing a known quantity of water.

2. Burning the food Food is fuel, and it is burnt inside our bodies using oxygen; the calorimeter simulates this in the lab. An ignition wire is used to set light to the food,
and as it burns, the energy released is transferred into the water surrounding the chamber, causing the temperature to rise.

3.  Calculating the calories When the food has been reduced to ashes, all the energy has been released. The difference between the start and end water temperature
is determined and multiplied by the number of grams of water that were contained within the calorimeter. This gives the number of calories.