When comparing different foods, it is important to carry out a fair test.

Several variables should be kept constant:

• the volume of water
• the mass of food
• the distance of the flame from the boiling tube

There are a few sources of error in calorimetry:

• it is difficult to maintain a constant distance between the burning food and the tube, varying the heat loss to the environment
• it is difficult to minimise heat loss when transferring the burning food from the flame to the tube
• in this method it is possible that incomplete burning of the crisp gives an inaccurate measurement of the mass burned

An improvement could be to use a bomb calorimeter:

• sample is burned in a sealed chamber to reduce heat loss to the environment
• sample chamber is surrounded by another chamber of water in which the temperature change is measured
• sample is burned in pure oxygen to ensure complete combustion