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Colloids and emulsions

Margarine and milk are both emulsions. An emulsion is a mixture of two liquids that aren’t normally compatible, such as oil and water. Emulsions contain a globular collection of fat/oil molecules.

One of the liquids forms small droplets (known as the discrete phase) that are surrounded by the other (called the continuous phase). The droplets are formed by whichever liquid is the lesser in volume.

Emulsifying is done by slowly adding one ingredient to another whilst stirring rapidly. This disperses and suspends tiny droplets of one liquid through the other. However, if you simply mixed oil and water together they would quickly separate into two layers, with the oil floating on top of the water. To produce a stable emulsion, you need a surfactant, otherwise known as an emulsifier.

Emulsifiers act as a liaison between the two liquids and stabilise the mixture. They do this by sitting at the interfaces between the oil molecules and the surrounding water. The water ‘sees’ only the ends that are like water and doesn’t ‘see’ any of the oil. Similarly, the oil doesn’t ‘see’ any of the water and only ‘sees’ the ends that are like oil. Egg yolk and gelatine both contain emulsifiers. In foods, the surfactant molecules are often proteins, or parts of proteins, that can be damaged by small changes in acidity and temperature. This is why when margarine melts, it often divides out into its constituent parts - water and oil.

Chemically, emulsions are colloids, which are mixtures composed of tiny particles suspended in another material that don’t mix. These particles are larger than molecules, but smaller than one-thousandth of a millimetre. The particles in a colloid can be solid, liquid and bubbles of gas. Similarly, the medium in which they are suspended can also be solid, liquid and gas (although gas colloids cannot be suspended in gas). Because the droplets in colloids are so small, they can easily pass through filter paper.

Pancakes

So why are pancakes as flat as a - well - pancake? It’s because pancakes (or more precisely, traditional crepes) don’t contain any sort of leavening agent.

The most common forms of leavening agents are yeast, baking-powder baking soda. Leavening agents create tiny bubbles of carbon dioxide, causing batter or dough to rise. In order for leavening agents to work, they need gluten to capture the carbon dioxide bubbles and hold them in the mixture. This is why it’s not a good idea to beat pancake mixture too much, as it creates too much gluten from the flour and makes your pancakes chewy.