Fats are esters

Won't you get stomach ache with all that butter on your sandwich? Hello! You're drowning your pizza in oil. Yeah! Olive oil is not the same fat as in butter.

Shut up! Fat is fat. Is Jenny right? Or are there different kinds of fat? This is how it is: Fats are esters based on glycerol connected to three fatty acids.

Okay, then. Let's start at the beginning. Here we have a type of alcohol: Glycerol. It has three carbon atoms. Each carbon atom is bonded to an O-H group, with oxygen and hydrogen.

And this is a carboxylic acid. It is an acid with a so called carboxyl group, which we write as C-O-O-H. Carboxylic acids with more than three carbon atoms are called fatty acids. Here is palmitic acid, which has sixteen carbon atoms. It's one of the most common fatty acids - found in both plants and animals.

When three fatty acids react with a glycerol molecule - three water molecules are released... And this forms: 'fat'. When an alcohol and an acid combine like this, we say they form an ester. There are many different kinds of esters. Only the ones made by glycerol and three fatty acids are called fats.

The fat molecule looks like glycerol, but with three long arms - so it's called: a triglyceride. See? Olive oil... butter... it's all...

fat. No, Jenny. Not really. There are many different kinds of fat. Look around the kitchen.

Fat is found in butter, olive oil, nuts, in the cheese on the pizza, in your bodies, in your brains, and in that avocado. All these fats look different - and have different properties. Animal and vegetable fats and oils are just big complex esters. The difference between a fat and an oil is simply in the melting points of the mixture of esters they contain. If the melting points are below room temperature, it will be a liquid - an oil, like olive oil.

If the melting points are above room temperature, it will be a solid - a fat, like butter. But why are they different, if all fats are 'esters' with 'three fatty acids'. There are different kinds of fatty acid. And they determine the kind of fat which is formed. Here's butyric acid (from butter)...

with only four carbon atoms. And here's - stearic acid - a long molecule with 18 carbon atoms. Fats are fairly stable molecules. But fat can also oxidize. Remember the reaction when the fatty acids and glycerol formed fat?

This is the same reaction - but in reverse. The fat molecule picks up water and divides into: carboxylic acid - and glycerol. In butter, this reverse reaction forms butyric acid - which smells really disgusting. This reaction is faster when the butter is warm - but is slowed down in the low temperature of the fridge. Better put the butter in the fridge, Jenny!

No rush, I might have... one more sandwich.