We are going to make some butter to put on the bread that is baking, and we’ll look at the molecules in that process.
Butter is made from cream. Cream has many different molecules in it, including the three in your collection. Recognize any of them?
[Water, fat and phospholipid.]
We know that fat and water don’t like to mix. Show students a tube of water, then pour in oil, and watch them separate into layers.
At the molecular level, the long tails of the fat molecules (made up of carbon and hydrogen) don’t want to be near the water molecules. (It’s because one of them has a charge [water] and one does not [fat].)
But in cream the water and fat molecules are able to mix together. Drops of fat in the water are stabilized by phospholipid molecules.
The long tails of carbon and hydrogen like to touch the fat molecules. The head has lots of red oxygen molecules, and you might also see a purple phosphorus and a blue nitrogen in there - this end of the molecule can touch water molecules.
Arrange your fat molecules into drops. Surround them with water molecules. Then add the phospholipid molecules so that they make a barrier between the fat and the water molecules, oriented so that all the molecules are stable.
You have made an emulsion, which is what cream is. Drops of liquid fat suspended in water.
This is what is in the jar of cream sitting on your desk.
In a moment we will shake the jar of cream - the emulsion drops are shaken apart and the component molecules come together with molecules they like to be with [that look like themselves]. Do the same with your molecular model.
The fat molecules join together in one big group as butter. The water separates in another group as buttermilk.
The phospholipid molecules can be part of the buttermilk as their own group, or they can surround a couple of water droplets trapped within the fat molecules (butter does have some water in it).
Now you can shake your cream to break open the fat droplets and form two separate fat and water groups: butter and buttermilk. Keep shaking until you have these two separate entities in your jar - the solid butter fat and the white liquid buttermilk.