Determining the Caloric Content of Foods
Introduction:
Students are familiar with the Calorie content of foods. In this lab students
experimentally measure the calorie content of some foods. This provides an
understanding of how calorie content of foods can be determined by experiment. This
lab also provides an opportunity to explain the difference between the food Calorie and
the chemical calorie.
To compare experimental values with those on the package, we recommend using only
freeze dried samples. Water, when burned, shows a loss in mass with no resulting heat
increase; varying amounts of water in food products lead to inconsistent results. Freeze
drying samples provides a greater consistency. We also recommend that the calorimeter
be covered on the sides and top with the insulating sleeve and cap to minimize heat loss.
We also suggest that the water not be stirred to show the maximum temperature increase.
After the sample is consumed, continue vacuuming until the temperature peaks; it could
take several minutes.
Purpose:
The purpose of this laboratory activity is to measure the calorie content of a food. This
value may be compared to that of other food types, or it may be compared to the value
shown on the food’s packaging.
Materials:
food calorimeter
oxygen tank and connectors
vacuum pump or water aspirator
6 V 2 A (ac or dc) power supply
1-L graduated cylinder
food sample
large ring stand
clamps
safety shield
analytical balance
Safety:
 Use a safety shield around the food calorimeter.
 Turn on the oxygen carefully to maintain a gentle flow of oxygen.
 Extinguish all flames in the laboratory.
 Always wear safety goggles and an apron in the laboratory.
 Never eat or drink in the laboratory.
Procedure:
1. Clamp the heat resistant platform to a ring stand at a height that permits it to be
lowered, in order to give access beneath the glass vessel.
2. Secure the glass vessel by a large clamp immediately above the platform. Be sure
the rubber bung (stopper) around the copper helix is tight.
3. Fill a 1 L graduated cylinder with distilled water. Use this water to fill the
calorimeter to just cover the upper coil of the copper helix. Determine the volume
by difference. Based on room temperature, use the density of the water to find the
mass of the water in the calorimeter.
4. Place the stirrer and plastic lid in position.
5. If required, cut a small ring from rubber tubing and place this ring on the
temperature probe or thermometer so that the tip or bulb is just above the top of
the inner calorimeter vessel.
6. Connect the vacuum source to the outlet of the copper helix.
7. Connect the tube below the heat resistant base to the oxygen tank.
8. Adjust the tank and vacuum so that a gentle stream of oxygen can pass in to the
combustion chamber. (20 kN/cm2) Adjust the oxygen stream with a pinch clamp
on the hose.
9. Place the nickel crucible on the heat resistant platform so that ignition spiral can
be lowered into it to touch the test food.
10. Connect the terminals to a 6V 2A power supply. Be careful not to exceed 6 volts
as the ingniter will break. If in doubt, check the power supply output with a
voltmeter.
11. Mass the empty nickel crucible to the nearest thousandth of a gram. Mass again
with the food sample inside.
12. Place the crucible in position on the heat resistant platform.
13. Place the safety shield around the apparatus.
14. Apply a moderate vacuum. Turn on the oxygen supply SLOWLY.
15. Agitate the water until a steady temperature is reached. Record this initial
temperature.
16. Lower the filament. Turn on the power supply and ignite the test substance.
17. Once ignited, raise the filament, turn it to the side, and immediately turn off the
power supply.
18. The test substance should burn steadily and brightly. If sputtering occurs,
decrease the oxygen supply until the food burns quietly.
19. Agitate the water continuously during combustion.
20. When the combustion is complete, turn off the oxygen supply and vacuum pump.
21. Continue to stir until a maximum temperature is reached. Record this maximum
temperature.
22. Allow apparatus to cool.
23. Mass the crucible again to determine the mass of the unburned residue.
24. Record the required data in the Data Section.
Data:
Food tested
______________________
Volume of water
______________________ mL
Mass of crucible
______________________ g
Mass of food
______________________ g
Mass of crucible and residue (after heating) ______________________ g
Mass of food consumed
______________________ g
Initial temp of water
______________________ ºC
Final temp of water
______________________ ºC
Temperature change
_____________________ ºC
Calories produced
______________________ cal
Calories/ g of food
______________________ cal/g
Calories per serving
______________________ Cal/ser
Calculations:
Determine the energy produced by the food and compare the total to the quantity
shown on the package. The formula is Q=m*c*ΔT where m is the mass of water,
c is the specific heat of water, and ΔT is the change in temperature of the water.
1. Determine the mass of the water inside the calorimeter in grams.
a. volume*density = mass
2. Determine the specific heat of water in cal.*g-1* ºC-1.
a. Specific heat of water = 1cal.*g-1* ºC-1
b. Since food energy is measured in kilocalories, specific heat =
0.001Cal.*g-1* ºC-1.
3. Determine the temperature change of the water in ºC.
a. Final temp – Initial temp = Temp change
4. Determine the energy absorbed by water in Cal.
a. Qw= m*c*ΔT
5. Determine the energy absorbed by the calorimeter in Cal.
a. Calorimeter constant * temp change = Qc
b. Qc=0.143Cal(ºC)-1 * ΔT
6. Determine the total energy produced by the burning food in Cal.
a. Qw+Qc=QT
7. Determine the energy produced per gram of food in Cal./g.
a. QT/mass of food burned
Calculations, opt:
8. Determine the experimental Calories per serving
a. Cal/g * g/serving = Cal/serving
9. Record the Calories per serving from the food package.
10. Determine the percent error.
Cal / servingonpackage  Cal / servingcalculated
a. Percenterror 
 100
Cal / servingonpackage
Questions:
1. Why was the calorimeter filled with water?
2. Why was the combustion chamber filled with oxygen?
3. Why was a vacuum pump used?
4. Which of the foods tested contained the highest number of calories per gram?