Why Make Milk Foam For Your Coffee?

Milk is a key ingredient in many coffee shops and an important element in making many coffee drinks. Learning more about its structure and the changes in foaming can help you make and develop a better-flavored coffee.

Milk is a nutrient-dense, complex liquid composed primarily of water but with hundreds of chemicals in it. These components can be divided into four major categories: protein (1-20%), fat (2-55%), carbohydrates and sugars (lactose 0-10%), minerals.

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Protein is the most affected substance during heating, and it is also the key to affecting the quality of milk foam. Let us look at the protein of milk more.

Generally, a protein can be defined as a molecule made up of one or more long chains of amino acids, which are held together by polypeptide bonds.

Maybe there are too many scientific words here. Still, the vernacular of the above sentence means that the proteins in milk are distributed throughout the liquid in different structures and sizes.

There are two main types of protein in milk: casein and whey. The two proteins have different structures and react differently under pressure, so when milk is heated and frothed, the two proteins change differently.

The structure of proteins is actually the difference in the arrangement of atoms. Casein in milk will form aggregates called micelles. These micelles are composed of 𝞪-, 𝞫- and 𝞳-caseins, which are proteins with primary structures.

Simply put, casein has a simpler structure than whey protein, and this difference directly affects how the two proteins behave when foamed by steam.

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Casein is more stable when heated than whey protein. In other words, casein retains its structure better when heated.

Whey protein has a more complex three-dimensional structure, and these structures will unfold when heated to 40 ° C. This process is called "heat denaturation". Whey protein will irreversibly lose its structure, resulting in changes in its operation after heating.

Any heating action affects the chemical structure of milk proteins, but how it does depends on the temperature and duration of heating.

Assuming you are using pasteurized milk, it means that before you get the bottle of milk, it has been sterilized at 72-80°C for 15-30 seconds.

Pasteurization denatures some of the whey protein, but not all of the whey protein is affected by the short heating program.

Overheating is what changes the taste of milk because of the sulfurous smell that develops during the heat treatment.

Come back here to discuss these proteins, and protein is the key to the success of milk foaming.

In its natural state, milk has active chemical groups hidden in the complex structure of whey protein, which is released when the whey protein unfolds during heating.

Because these chemical groups are reactive, they form new chemical chains with other whey components in these unfolded structures, which can have an effect on the foaming of the milk.

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How do these chemical changes mentioned above affect your coffee?

When we froth milk, we force water vapor and air into the milk by heating, so the protein forms spheroids in the air and turns into stable bubbles.

Protein chains in milk are polar opposites: hydrophilic at one end and hydrophobic at the other. As the protein unfolds during denaturation, the protein at the hydrophobic end tries to stay away from the water in the milk.

This means that the bubble structure of each milk foam is filled with protein chains at the hydrophobic end and the hydrophilic end in the milk liquid. This structure helps the bubble maintain its intact shape.

When the milk foams to 30-40°C, it becomes unstable and large bubbles form rapidly. Raising the temperature to 60°C stabilizes the milk foam and improves its texture and density. Smaller and better-dispersed bubbles are formed at higher temperatures.

Fat plays an important role in stabilizing milk foam. When the temperature exceeds 40°C, all the lipids of the milk are melted. This liquid fat helps prevent the bubbles from gathering by forming a film on the surface of the bubbles (so as to avoid the formation of large bubbles).

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But be careful to avoid heating to too high a temperature, which will not only cause the milk to produce a sulfurous smell but also cause the milk to fail to foam.

Proteins in their natural state attach to the air bubbles, preventing small bubbles from clumping into larger ones. If you continue to heat the milk at this point, you will denature more of the protein, thereby destroying its original properties and failing to stabilize the bubbles.

This also explains why you can't re-foam milk. Even if you reheat it, the protein in the milk won't have enough natural structure to form stable bubbles.

Milk with a higher lipid content may help to form more stable milk foam, but butterfat is the predominant fat in milk, which is a large and heavy fat.

More than 95% of milk fat is in small spheres of 0.1-15 microns in diameter, and in the case of fat so large and heavy, it can compress the air bubbles and cause them to burst. Fat will also cover other flavors, meaning that some of the flavor profiles of the coffee bean itself may be sacrificed.

But if you want to opt for skim milk, keep in mind that fat also affects the appealing taste of cappuccinos and lattes.

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When you want to pick and choose the milk to add to your coffee, it's all about the protein content of the milk. Without protein, milk cannot froth. The high protein content of products like milk for coffee is also for this reason, but if you can control the temperature effectively, you can also use regular milk for frothing.

The ideal temperature for milk foaming is between 60-63°C. If it is lower than this temperature, unstable milk foam and large bubbles may be obtained; if it is higher than this temperature, excessive protein denaturation will result in the protein in the milk. There won't be enough natural structure to form stable bubbles.

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Foaming with skim milk may result in a stable milk froth, but it will lack the nice mouthfeel that butterfat brings. By using low-fat milk, it is possible to obtain both stable milk foam and full-tasting milk.

Knowing the chemical composition of milk can help to make a better espresso-based drink by understanding how the protein in milk changes. You can avoid milk foam defoaming.

Come and test the foaming principle of milk with a steam wand today!

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• The protein in milk is the most affected substance during heating, and it is also the key to affecting the quality of milk foam and the success of foaming.
• Proteins are mainly divided into casein and whey protein, and whey protein has a more complex three-dimensional structure. These structures will unfold when heated to 40 °C, a process called "thermal denaturation".
• High-temperature sterilization treatment or excessive heating will change the taste of milk. In addition to producing a sulfurous smell, it will also cause foaming failure.
• Milk fat plays an important role in stabilizing milk foam, and milk with a higher lipid content may help to form a more stable milk foam. But fat can also cover other flavors, which means that some of the original flavors of the coffee beans may be sacrificed.
• Even with reheating, the proteins in milk don't have enough natural structure to form stable bubbles.
• The ideal temperature for milk foaming is between 60-63°C. If it is lower than this temperature, unstable milk foam and large bubbles may be obtained; if it is higher than this temperature, too much protein will be denatured.

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