Study kit for Milk Components

Quick Answer: This milk components study kit is used to separate and identify the main constituents of milk: the protein casein, fat, the sugar lactose and minerals such as calcium. Students use classic food tests and a simple acid precipitation to show that a uniform white liquid is really a mixture.

Taking Milk Apart

Milk looks like a single substance, but it is an emulsion of fat droplets in water that also carries dissolved lactose, minerals and suspended protein. Adding a little acid, such as vinegar or a dilute laboratory acid, to warm milk makes the casein clump into curds, because acid brings the protein to the pH at which it is least soluble. Filtering separates the curds from the whey, and each fraction can then be tested.

The curds give a positive biuret test for protein, turning the blue reagent violet, and they hold most of the fat, which shows up as a grease spot on paper or with a fat stain such as Sudan III. The whey contains lactose, a reducing sugar that gives an orange-red precipitate with Benedict’s or Fehling’s solution on heating, and calcium, which gives a white precipitate with ammonium oxalate solution.

The title does not list the kit’s reagents, so compare its contents with the tests you plan to run. The work is done at test-tube scale, with stoppered test tubes for the shaking steps and a water bath for heating.

Applications

• Food chemistry practicals on the composition of a familiar mixture
• Comparing whole, skimmed and plant-based milks with the same tests
• Showing the precipitation of a protein at the pH where it is least soluble
• Home science and nutrition courses that study the nutrients in foods

Specifications

Care & Handling

• Use fresh milk and discard it after the practical; do not leave milk samples in the lab overnight.
• Heat Benedict’s or Fehling’s tests in a water bath rather than directly, to avoid spitting.
• Wear eye protection with biuret reagent and Fehling’s solution, both of which contain sodium hydroxide.
• Never taste any sample or product in the laboratory, including the curds.

Why Choose LabEquip

Chemistry, biology and home science teachers choose milk component kits because students already know the material and are surprised by how much it contains. LabEquip lists this kit under chemistry lab equipment; send your planned tests through the contact page to check the reagents match.

Frequently Asked Questions

Why does milk curdle when acid is added?

Casein particles in fresh milk carry a charge that keeps them apart. Acid lowers the pH to around the point where the protein carries no net charge, so the particles clump together and separate as curds.

Which sugar is detected in milk, and how?

Lactose, a reducing sugar. Heated with Benedict’s or Fehling’s solution, the whey changes from blue through green to an orange-red precipitate, showing that a reducing sugar is present.

How can the fat in milk be shown?

Rub a drop of milk or curd on filter paper and let it dry: a translucent spot that does not disappear shows fat. Alternatively, shake the sample with a fat stain such as Sudan III, which colours the fat droplets red.

Can plant milks be tested with the same kit?

Yes, and comparing them is instructive. Many plant milks contain little or no lactose and different proteins, so they may not curdle in the same way or give the same sugar test result.

How is calcium in milk detected?

After removing the curds, add ammonium oxalate solution to the whey. A white precipitate of calcium oxalate shows that calcium is present.

What does the biuret test show?

It detects the peptide bonds in proteins. Adding biuret reagent to a protein sample turns the mixture from blue to violet, and the curds from milk give a strong result.

Last Updated: September 2026