Milk Steaming Science!

The foaming explained

As promised this week is all about the sciency side of steaming milk, there’s parts to this that are abit much to go into so lets just cover the basics and not worry too much on the full naming of everything.

Milk composition

Cow’s milk has two proteins making up roughly 20% as whey and 80% as casein, protein in milk is important as it helps form the foam when steaming.

Whey is the same protein as used in alot of protein powders and is a by-product of making cheese while casein is the protein that makes milk white in colour.

Steaming

When steaming milk there are two factors being introduced to the liquid, air and heat. Air being added is important as the proteins in milk are made up of amino acids, these molecules are made up of a hydrophobic side and a hydrophilic side, the phobic side doesn’t want to be in contact with liquid and so when air is introduced to the milk in steaming, the phobic side of the molecule will bind to the air bubble, this causes the bubbles to become more stable and hold together with the liquid.

The heat aspect of steaming unfolds the amino acid molecules and allows for the molecules to bond with the air bubbles being introduced more easily, but too much heat is an issue. When milk if heated too much, the proteins become denatured causing the amino acid’s bonds to break, this often gives off a custard/ egg like smell.

Properties

Milk also contains fat which competes with the steamed milk’s air bubbles to connect with the hydrophobic side of the amino acids. These fats can cause less stable bubbles within the milk which is why skimmed milk forms very strong foam when compared to that of other milks. Skimmed milk due to its strong foam is alot harder to pour for latte art, so if you order skimmed drinks please don’t hate the wonky heart pattern you may get.

In regards to alternative milks, if the box/ carton say “for baristas” then you can rest assured it will have added oils or fats that help emulsify the the liquid and allow for foam to form when steamed. The added oils also help with mouthfeel and flavour release for the drink.

Alright that one was a wordy clutter of terms but hopefully now you have a bit more of an insight into the world of milk foaming!

Have a great week and some even better coffees!