Monday 13 May 2013

Science: How to make your own butter

Believe it or not milk and cream are emulsions.  It is possible for tiny particles of two substances that seem unable to mix to suspend in around each other.  So the link above shows us how to make an emulsion but this experiment shows us how to split up an emulsion. It is both interesting scientifically but also very useful to make a very yummy food - butter.

All you will need is:
  • A bowl
  • A wooden spoon or a whisk (Or if your not feeling very strong you can use an electric whisk instead)
  • Cream
Before you start you should...

Make sure you are working with a clean bowl or clean jar and it is really important that your double cream or whipping cream is room temperature.
What you need to do...

All you need to do to make butter is beat the cream or vigorously shake your jar of cream. First the cream will thicken but then it will separate into butter (the solid) and buttermilk (the liquid).

You can also put your cream in a clean jam jar, close the lid tightly and shake for about 10 minutes, maybe more until you separate the butter from the buttermilk.  WARNING: this will make your arms ache more. 

Questions you can ask when doing your experiment:

Can you see changes happening inside the bowl/container?

Does it start to feel different when you are whisking/shaking it?

Why do you think that happened?
The butter is done when it has completely separated from the liquid and forms a solid, single clump surrounded by a liquid, this liquid is buttermilk.

Why does this happen?

Well, milk is mostly water with about 5% to 10% protein and fat globules whereas thick cream contains around 30% fat globules. A globule is a really tiny membrane filled with fat molecules. These globules are so very small and fat is less dense than water that it floats! This is what makes a colloid, a suspension that stays that way. 

When we beat the cream, whichever way you chose in this end, the globules smash open letting out molecules of fat - a bit like when a water bomb explodes and the water escapes.  The molecules of fat that spills out, clump together with the other fat molecules that have escaped from other globules that have burst open.  This is what causes the fat molecules to separate from the watery buttermilk.  . As this process continues, two new substances are formed: a solid (butter) and the remaining liquid (buttermilk)!
Things we learn from this experiment...
  • About molecules
  • About emulsion
  • About colloids

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