How do they do it? I mean, how did they work out the calorific content in an egg for example?
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How do they calculate/derive the calories in a food product?
- Thread starter Herr Tubthumper
- Start date
severnside gull
Well-known member
Made me wonder too so from a quick google....................
The method originally used was to take a sample of the food and burn it it a device called a bomb calorimeter which would give the amount of heat released when the sample burned. The problem with this method is that not all of the energy stored in foods like apples is going to get used when you eat them. Apples contain a lot of fiber in the form of cellulose and pectin that aren't digested. A more accurate method is to extract individual food components such as fats and starches and then calculate the total calorie content of the food based on percentages of calorie containing components. The labels on foods are accurate and you can rely on them to plan a diet. Fresh fruits and vegetables are another matter, the amount of water, sugars, starches and fats can vary considerably, however, the calorie guides are accurate enough to serve for diet planning purposes
The method originally used was to take a sample of the food and burn it it a device called a bomb calorimeter which would give the amount of heat released when the sample burned. The problem with this method is that not all of the energy stored in foods like apples is going to get used when you eat them. Apples contain a lot of fiber in the form of cellulose and pectin that aren't digested. A more accurate method is to extract individual food components such as fats and starches and then calculate the total calorie content of the food based on percentages of calorie containing components. The labels on foods are accurate and you can rely on them to plan a diet. Fresh fruits and vegetables are another matter, the amount of water, sugars, starches and fats can vary considerably, however, the calorie guides are accurate enough to serve for diet planning purposes
beorhthelm
A. Virgo, Football Genius
- Jul 21, 2003
- 36,452
i recall in science class you burn it under a testtube of water and take the temperature before/after, the rise is used to work out the amount of energy. i believe they do the same with slightly higher tech kit
one interesting point this raises is wether you would use all those calories or not. sugars, fats, starchs, protiens, fibre, all equate to certain calorie values, but you might not digest or metabolise them.
one interesting point this raises is wether you would use all those calories or not. sugars, fats, starchs, protiens, fibre, all equate to certain calorie values, but you might not digest or metabolise them.
cliveh27
New member
There are two methods:
Either
a) Burn the food in oxygen and measure the amount of heat given off, or
b) Taste the food. The better it tastes, the more calories it contains.
Either
a) Burn the food in oxygen and measure the amount of heat given off, or
b) Taste the food. The better it tastes, the more calories it contains.
They no what is included in the product and then they can work it out. There are four catergories fat protein sugar and others that include water. For each gram of fat this equalls 9 calories for each gram of protein and sugar this equals four calories and others such as water have no calorie content therefore by knowing the ingredients they know how many calories are in it. Example a choclate bar weighting 50 grams has 20 g of sugar and 25g of fat and 5 grams of protein you can work out that 20 x 4 equals 80 25 x 9 equals 175 and 5 x 4 equals 20 they add the 175 20 and the 80 together showing how many caalories there are !
They no what is included in the product and then they can work it out. There are four catergories fat protein sugar and others that include water. For each gram of fat this equalls 9 calories for each gram of protein and sugar(sometimes known as carbohydrates) this equals four calories and others such as water have no calorie content therefore by knowing the ingredients they know how many calories are in it. Example a choclate bar weighting 50 grams has 20 g of sugar and 25g of fat and 5 grams of protein you can work out that 20 x 4 equals 80 25 x 9 equals 175 and 5 x 4 equals 20 they add the 175 20 and the 80 together showing how many caalories there are !
They no what is included in the product and then they can work it out. There are four catergories fat protein sugar and others that include water. For each gram of fat this equalls 9 calories for each gram of protein and sugar(sometimes known as carbohydrates) this equals four calories and others such as water have no calorie content therefore by knowing the ingredients they know how many calories are in it. Example a choclate bar weighting 50 grams has 20 g of sugar and 25g of fat and 5 grams of protein you can work out that 20 x 4 equals 80 25 x 9 equals 175 and 5 x 4 equals 20 they add the 175 20 and the 80 together showing how many caalories there are !
SeagullSongs
And it's all gone quiet..
They take a 1 gram sample of the food and put it in a bomb calorimeter and burn it.
Then you measure the temperature rise of a known mass of water.
The formula E = m*c*delta theta (temperature change) is used.
m = mass of water in kg
c = specific heat capacity of water (4180)
temperature change = speaks for itself.
E will be in Joules, and there are 4.18 joules to a calorie.
Multiply this by the number of grams of the food there are, et voila.
P.S. My physics exam on this module went pretty well the other day!
Then you measure the temperature rise of a known mass of water.
The formula E = m*c*delta theta (temperature change) is used.
m = mass of water in kg
c = specific heat capacity of water (4180)
temperature change = speaks for itself.
E will be in Joules, and there are 4.18 joules to a calorie.
Multiply this by the number of grams of the food there are, et voila.
P.S. My physics exam on this module went pretty well the other day!