Why does milk not like cola?

glass jars with yoghurt and coconut half in the background

Fresh cow’s milk, condensed milk and soy milk have one thing in common: they contain proteins. These are important for our nutrition. These proteins become solid when they come into contact with a sufficiently strong acid, such as phosphoric acid, which is contained in cola. How do proteins from different types of milk react with cola?

Before you get started

If you are experimenting at home:
1. Let your parents know and discuss the experiments with them beforehand.
2. Do not eat or drink at your workspace.
3. Wash your hands thoroughly before and after the experiment.
4. Be careful and cautious with the materials.

Graphic figure boy pouring liquid in flask

bottle with cola and three containers with milk

You will need

Cola
Different kinds of milk
Water glasses
Measuring jug
Tablespoon

Let’s get started!

1. Measure cola

Take a measuring jug and pour 100 ml of cola into each of the three glasses.

three glass jars with light brown milky liquids

2. Add different types of milk

Add one tablespoonful of milk to each glass:
Soy milk
Condensed milk
Low-fat UHT milk

The photo shows the glasses immediately after adding milk to the cola.

three glass jars with medium brown milky liquids

3. Observation after 15 minutes

Observe what has happened: Can you see whether the color has changed in all the glasses? Can you see whether any solids have formed ‏(this is also called "flocculation")? Are there any differences?

glass jar with clear liquid above solid residue

4. Observation after one night

Leave the three jars overnight and look at them again afterwards. What has happened overnight? -> Depending on the type of milk, the proteins have flocculated to different degrees and settled at the bottom of the jars. By adding the acid ‏(cola), the milk proteins could be separated as solids.