What is the chemistry of milk?

What colour is milk?


Read and discuss DAIRY PRODUCTS to find out why some dairy products are liquid and other are solids.

Complete the activities in EXPERIMENT WITH LIQUIDS AND SOLIDS.


Read and discuss WHAT HAPPENS TO MILK AT A DAIRY to explore how natural resources and human activities are part of the process that brings food from the farm to your table.

Complete the activities in EXPLORE THE CHEMISTRY OF MILK.

liquids and solids

How many dairy products are you familiar with? There are many dairy products. Some are liquids. Others are solids.

How many dairy products can you identify that are solids? How many can you identify that are liquids?


Foods go through different types of changes. Sometimes, these changes occur when you prepare or cook food. Other times, these changes occur naturally. This is an example of a physical change and it changes the state of matter of the food. There are three states of matter – liquid, solid and gas.

Think about ice cream. If the ice cream melts, it changes from a solid to a liquid. Its state of matter has changed. However, it is still ice cream. When you mix fruit into yogurt, you might change its colour. However, the yogurt is still yogurt and the fruit is still fruit.

Next, think about a banana. As it ripens, it also changes colour. However, more than the colour changes. The banana gets softer and its sugar content changes. Ripening fruit is an example of a chemical change.

Now, consider milk. Milk and cream are liquids. If you leave milk or cream out of the fridge overnight or for a few days, its state of matter changes. Solid chunks can form in the milk and cream. However, this is a chemical change because a new substance is being formed. The sour smell that results is also a sign that a chemical change is taking place!

What dairy products do you think are made that involve chemical changes? Why do you think this?



make it chocolate

Do you think brown cows make chocolate milk? Watch this video to find out!

Is chocolate milk an example of a physical change or chemical change? Why do you think this?

changing liquids to solids

The use of milk to make dairy products was part of the history of Alberta. Early settlers knew that cream came from milk. Milk contains water and fat. Since fat is less dense than water, the milk would separate if it was left to sit. Once the fat rose to the top of the milk, it was skimmed off as cream.

Settlers would set their milk out overnight in wide-mouthed containers. In the morning, they skimmed off the cream. The cream was then stored in a cool location to avoid turning sour.

Once enough cream was collected, it was shaken or churned until the cream turned into butter. Salt was then added to the butter and kneaded to remove any excess milk. The salted butter was shaped into a loaf or pressed in a butter crock for sale to other homes or stores.

Did you know that originally, buttermilk referred to the liquid that was left over from churning butter into milk? Today, buttermilk is prepared from skim or low-fat milk. Bacteria is added to ferment the milk. Did you also know that this homemade butter could be melted and mixed with the resulting buttermilk to make it into cream again?

Does making butter involve a physical or chemical change? How do you know this? When is butter also a mixture?

Photo Source: Cochrane’s farming landscape has gone through change (March 13, 2014): Cochrane TODAY