Determination of Crude Fat in food products using Soxhlet apparatus

We will see how to calculate crude fat in a food sample using the Soxhlet apparatus.

What is Crude Fat-

When we use any solvent for the extraction of fats from any compound, we may not get pure fat, rather we may get a mixture containing some other compounds also. This mixture is called Crude Fat.

So, Crude fat is some amount of extracted fat plus some extra compounds like free fatty acids, cholesterol, lecithin, volatile oils, resins fat-soluble vitamins like A, D, E, K.

In this post, the procedure of determination of Crude fat by the Soxhlet apparatus is described.

Soxhlet apparatus Principle-

A schematic representation of a Soxhlet extractor 1: Stirrer bar 2: Still pot (the still pot should not be overfilled and the volume of solvent in the still pot should be 3 to 4 times the volume of the soxhlet chamber)   3: Distillation path 4: Thimble 5: Solid         6: Siphon top 7: Siphon exit 8: Expansion adapter 9: Condenser 10: Cooling water out 11: Cooling water in

Principle- of Soxhlet apparatus- To extract lipids from a solid material.

The mixture from which the crude fat is to be extracted is kept in the Still pot numbered 2.

The still pot is heated from the bottom bed, so the solvent mixture starts vaporizing and starts rising via the Distillation path numbered 3 as shown in the above figure.

The vapor slowly starts flooding into the thimble.

CELLULOSE THIMBLES.                                     Source-


Few vapors also reach the condenser (See 9 in the figure). So, the condenser condenses those vapors and the resulting liquid also falls into the thimble and surrounding it.

The condensed solvent that falls into the thimble containing the sample dissolves it thoroughly.

The above step repeats itself until the thimble in the soxhlet apparatus is completely full. Then the excess condensed solvent is returned to the distillation flask (Still pot i.e. 2).

The thimble is made up of cellulose matter and it has good filtration specificity, so it takes care that no solid content comes out of the thimble into the still pot.

This cycle in the Soxhlet apparatus is repeated and the mixture solvent gets concentrated because of its multiple evaporation and condensation steps.

Finally, after a number of repeated steps in the soxhlet apparatus, the solvent is evaporated using a Rotary evaporator and we get the extracted crude fat which was earlier dissolved in it.

The thimble is now having the leftover content which was insoluble with the solvent and hence it is discarded off.

Hence, the main use of the Soxhlet apparatus is to extract lipids i.e. fats from a mixture with the help of organic solvents.

The fat content is measured by the weight loss of the sample or the weight of the fat removed.

Procedure to determine fat content by Soxhlet apparatus-


1. Weigh around 5-10g sample into the thimble. ( For instance, we took Indian fried NAMKEEN from Haldirams as a sample)

2. Take the empty weight of the Still pot/ or flask, whichever you are using.

3. Fix the thimble filled with sample properly in the apparatus.

4. Add petroleum ether in almost (3/4th of the still pot)

5. Run the instrument for 2 hours.

6. After 2 hours, place the still pot in a hot air oven at 80°C for half an hour.

7. Now again take the dried weight of the Still pot after oven drying.

Calculations (hypothetical)



So, the amount of Crude fat in the sample taken is 34.592%.

This post was all about how to determine the crude fat content in a given food sample using the Soxhlet apparatus.



Have a look at other food technology posts-

Share this article :)

Leave a Reply

Your email address will not be published. Required fields are marked *