Espresso Blog

The Science Behind Milk Frothing—And Its Importance For Espresso Drinks

At Espresso Services and coffee shops across the country, careful attention is paid to the quality of the coffee that goes into lattes, cappuccinos and other espresso drinks. But milk is an equally vital component in these beverages.

How you steam and froth your milk is just about as important as grinding and tamping your coffee correctly. And having some understanding of the chemistry around steaming and frothing may help you make the best tasting espresso drinks your customers could ask for.

Milk’s Magic Ingredients:

Three solids are suspended in milk that directly impact its flavor and texture—whether cold, hot or frothed:

· Lactose (or milk sugar)

· Fat

· Protein

Lactose is less soluble at cooler temperatures (i.e., its dissolves more slowly), which is why milk is relatively unsweet when it’s cold. When the milk is heated, lactose dissolves more readily, giving it a sweeter taste.

As for fat content, obviously skim milk contains no fat, while 2% milk contains 2% fat and whole milk contains 4% fat. The more fat, the richer and creamier the milk will taste. The percentage of fat also impacts volume and stability of milk when it’s frothed.

When whole milk is frothed it’s more stable than skim milk, but it will be less voluminous. The opposite is true for skim: you will see a thinner, less stable froth but with greater volume. To strike a balance, you can use milk that is over 5% fat to create a froth that is both thick, stable and voluminous.

Breve, anyone?

The proteins in milk are whey and casein—both of which help create the froth. The structure of froth depends upon the structures of these proteins. They work differently, but when heated, they react the same and are stable at about 140 degrees. After that, they become susceptible to denaturing, which changes the shape and texture of the froth.

Warning: You will get an inferior froth when you steam milk a second time. Train your staff to steam only the amount of milk they need for the drink(s) being made at the moment. Because constantly throwing away milk can become expensive, we understand that it is not always practical to discard already steamed milk. So if you do decide to re-steam it, only do it once!

Now, check out this simple but quite helpful tutorial on steaming milk. It includes great use of graphics to help you gauge your technique!

And always feel free to contact us with any questions about milk steaming.

Topics: espresso based drinks, steaming milk

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