Principles of Milk Frothing Latte Art Tutorial Guide to Creating Dense and Smooth Milk Foam

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Introduction

In a good latte, besides espresso, milk plays an important role. You may have noticed that most coffee shops use refrigerated fresh milk for making milk coffee, and rarely use milk that can be stored at room temperature. Why is this? Must the milk for latte coffee be refrigerated fresh milk? How to choose suitable milk for coffee latte art?

What are the main components in milk and how do they affect a cup of coffee?

Milk is mainly composed of protein, fat, carbohydrates, and ash. Among these, protein plays a role in forming and stabilizing milk foam, fat adds richness to coffee and further stabilizes milk foam, while carbohydrates add sweetness to coffee.

Protein

Milk is mainly composed of two major parts: casein and whey protein.

When we use a steam wand to heat and stir milk, whey protein gradually "unfolds" to form a membrane that wraps around gas, producing many bubbles of different sizes. The bubble surface is covered with surfactant-containing casein micelles, creating a certain degree of surface tension at the contact point between bubbles and liquid, thus stabilizing the bubbles and preventing them from breaking easily.

Fat

The content of milk fat determines the richness of milk and the subsequent stabilizing effect on milk foam.

Comparing skim milk, whole milk, and cream, it's not difficult to find that skim milk gives a thin and light feeling to the palate; whole milk gives a rich and smooth feeling to the palate; while cream gives a heavy and thick feeling to the palate.

When milk is heated above 40°C, the lipids in milk melt. The melted lipids are lighter in density and can attach to the bubble surface to form a membrane, once again "reinforcing" the bubble surface, making the milk foam more stable when fused with coffee. This also explains why the foam from skim milk dissipates faster than that from whole milk after fusion with coffee.

Carbohydrates

The main carbohydrate in milk is lactose.

The sweetness of lactose is not as sweet as fructose. If we take the sweetness of sucrose as 1.0, lactose only has 0.16. Interestingly, although the sweetness of lactose is not obvious, the perceived sweetness in taste varies with changes in milk temperature.

Between 60°C-70°C is when lactose and other sugars are most "active." When milk is frothed to this temperature range and fused with coffee, you will find that this milk coffee, without added sugar, gives a sweet feeling both in smell and taste. (Of course, if the espresso is not extracted properly, even the sweetest milk cannot save bitter coffee~)

What are the requirements for milk used in coffee latte art?

As mentioned above, protein and fat are the main factors affecting milk's foaming ability and foam stability. So does higher protein and fat content in milk make it more suitable for making coffee latte art foam?

Not necessarily~ A higher protein content can indeed improve milk's foaming ability. However, if the fat content is too high, the dissolved weight exceeds what the bubbles can bear, and the foam will collapse. Previous research has shown that milk with approximately 3.2% protein content and 3.7% fat content achieves a good balance in foaming ability and foam stability. Secondly, too high fat content in milk can mask the flavor of coffee.

Must latte coffee be made with refrigerated fresh milk?

Actually, as long as the protein and fat content are sufficient, there is no requirement that latte coffee must be made with refrigerated fresh milk. UHT room temperature milk can also be used to make latte coffee. So why do coffee shops prefer to use refrigerated milk to make latte coffee? FrontStreet Coffee has talked with many people in the coffee industry and compiled various viewpoints.

The main reason for choosing fresh milk is freshness. The shelf life of refrigerated fresh milk is generally 7-15 days, while ultra-high temperature (UHT) treated milk can last for more than a month without refrigeration. This gives consumers a direct impression: UHT room temperature milk is too low-end and shouldn't appear in coffee shops.

Secondly, when comparing room temperature milk and fresh milk, most people feel that refrigerated fresh milk is generally richer than UHT room temperature milk. Even when both have similar protein and fat content, there is still a perceived difference.

Next is foam stability. Although UHT room temperature milk can also produce fine and delicate foam, the foam dissipates faster than fresh milk foam after fusion with coffee. Many people find in practice that the stability of UHT room temperature milk is uncertain - one batch of milk might have good foam, while the next batch's foam suddenly becomes unstable.

Based on the above viewpoints, FrontStreet Coffee believes that both fresh milk and UHT room temperature milk can be used to make latte coffee. However, compared to milk quality, fresh milk has a more stable supply chain and more consistent quality than UHT room temperature milk, providing better guarantees for daily production.

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