Why milk matters

Adding milk to espresso is a longstanding tradition, but there’s more depth to the pairing than meets the eye.

Lattes, Flat Whites, Macchiatos – each are made with the same two ingredients: milk and espresso. And yet, they can taste and feel dramatically different.

Why? It’s all in the milk.

Milk’s many flavours

Milk is complex. It’s essentially made up of microscopic protein particles, fat, sugar, and a handful of other things that are evenly distributed in water.

Here’s how each of these elements contribute to milk’s sweet, creamy experience…

Proteins: the foam builders

Proteins (primarily caseins and whey in milk) are what make velvety smooth milk foam possible.

When milk is steamed, the protein molecules unravel and begin to cling to the steam’s air molecules. When steaming stops, the proteins curl back up around the air to create a fine foam structure.

The trapped air will eventually wiggle its way free, but the more proteins a milk has, the longer it’ll take.

Sugars: the sweeteners

Lactose is the main sugar in milk. Made of both galactose and glucose, it’s only 16/100 as sweet as granulated sugar when cold. However, two interesting things happen when lactose meets steam;

  • The water in hot steam causes the lactose molecules to unbind, causing them to taste sweeter.
  • Human tongues perceive more sweetness in warm liquids than cold ones.

The end result is milk that’s significantly sweeter than it was just seconds earlier.

Lactose-free milk is often exceptionally sweet. The enzyme that’s used in the lactose extraction process leaves a super-sweet reside from the galactose and glucose.

Fats: the flavour-boosting companions

Fat globules cling to your tongue like glue. This is what creates that smooth, creamy mouthfeel.

Some flavours get trapped in the fat for a prolonged flavour release, like vanilla and chocolate.

For coffees with tasting notes like chocolate and nuts, fats are flavour-boosting companions. However, fruitier coffees tend to taste less fruity when milk fats come into play.

Whole, skim and semi-skimmed milk

There are more fats in whole milk versus skim and semi-skim milk, meaning your coffee will have a creamier mouthfeel. The flavour release of nutty and chocolate notes are also prolonged.

In skim milk, proteins play a larger role, meaning it will take longer for the foam to break down, but the overall mouthfeel’s less creamy.

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