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The science behind milk frothing and steaming. Why do some foam better than others?

October 21, 2022

Milk foam can bring a milk-based drink to a new gourmet level… and it’s not just for cafes. Whether you’re making a cappuccino, hot chocolate, golden milk, your favorite tea latte, a fancy protein shake, or a “puppuccino” for your pets, you can froth milk at home!

Milk frothing and milk steaming are similar but different. 

Both are foamed milk, and both add air and change the milk’s texture. But, they are distinctly different on the tongue. If you want to master the perfect milk-based drink at home, you’ll need to know the difference. 

Steamed milk is created using a wand that forces powerful water vapor into the milk. The steam breaks down the fat in the milk and creates tiny air bubbles. Steamed milk is sometimes referred to as “microfoam”. People often describe it as smooth and velvety and sweet. 

Steamed milk is used for lattes and macchiatos.

Frothed milk is created by incorporating air into milk to create large voluminous bubbles. No steam or heat is needed. Compared to steamed milk, frothed milk has a much lighter feel and can be described as “drier”. It also holds its shape better. 

The most classic use for frothed milk is the cappuccino, which is one-third espresso, one-third steamed milk, and one-third frothed milk.

Now that we understand the difference, let’s get to the science behind it!

The sweetness is affected by the lactose (milk sugar).

Lactose (milk sugar) is less soluble at room temperature. That’s why cold milk is relatively unsweet. Lactose breaks down when heated. So, steamed milk will be sweeter than frothed milk. This is something to keep in mind when creating your delicious homemade milk mocktails.

The proteins in the milk are whey and casein, which both help create the structure and stability of the froth.

When frothing or steaming, the proteins unravel (or denature) and create spheres around the air. This is what makes the bubbles. 

Fat content affects the feel of the foam. More fat creates a richer, smoother, velvety texture. 

The higher the fat content of the milk, the creamier the milk foam. Each type of milk has a different fat content. For most store bought dairy, here’s a breakdown:

  • Skim milk - 0% fat
  • 2% milk - 2% fat
  • Whole milk - 3.5% fat
  • Half & Half - 10% fat
  • Heavy Cream - 36% fat

All of Miller’s cow milk is full fat and non-homogenized. And, our herd of 80% Jersey cows and 20% Jersey crosses produce the fattiest milk around, just shy of 5%. 

The fat content plus temperature affects the volume and stability of the foam. 

This is because fats present themselves as globules, spheres surrounded by a membrane. When intact at colder temperatures, these globules can puncture bubbles. Ever have the moment of “Where’d the foam go?” But, when heated, the globules break down. The liquified fat can surround air pockets just like denatured proteins, which stabilizes the foam.

Milks with less fat (like skim milk) will create more stable and voluminous frothed foams at temperatures below 113F. But milks with more fat (like whole milk) will create more stable and voluminous steamed foams at temperatures above 113F. 

Raw milk will be inconsistent, and pasteurized milk will be consistent.

Raw milk has living enzymes and bacteria that break down lactose, proteins, and fats. The longer it sits (even in the fridge), the more it ferments. That means that fresh raw milk will likely make better milk foam than soured raw milk.

Pasteurized milk, on the other hand, is dead. It will produce more consistent milk foam every time. But, even with pasteurized milk, the fresher the milk, the better the foam.

Still hung up on the “puppiccino” from the first paragraph? Yea, it’s definitely a thing and can increase the quality of your pet’s life.

Enrichment is the act of improving or enhancing the value of an experience. For pets, this could mean exploring the outdoors or grooming practices, but enrichment can also be done with food. 

Giving your pet a variety of foods that tantalize their taste buds and tickle their tongues with texture add value to their life. Milk foam for pets? Yes, please! You can find a recipe for a “puppaccino” and a “hot dogolate” here.

Have you succeeded or failed with milk foam? What’s your favorite milk-based drink? What kind of frother/steamer do you use?

I’d love to hear from you. Comment below (no account required - start typing for the guest option to appear) or contact us.

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Sources:

  1. Steamed Milk Vs Frothed Milk: What’s The Difference?
  2. The Science of Steamed Milk: Understanding Your Latte Art
  3. The influence of temperature on the foaming of milk
  4. What Should Your Cappuccino Milk Temperature Be?
  5. Milk Components: Understanding Milk Fat and Protein Variation in Your Dairy Herd
  6. DIY Enrichment Activities to Keep Your Dog Happy
  7. How to Make Puppuccino and Hot Dogolate



Marie Reedell

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