It's So Cold Outside, Why Don't You Make My Latte Hotter?

In winter, there's probably no coffee more popular than a hot latte—unless it's a flat white! Either way, we're talking about milk coffee~ I believe that milk coffee sales at every coffee shop have seen linear growth, and with the increase in hot milk coffee, there are also some small accompanying demands. For example: "Boss!!! The temperature is dropping too quickly, could you please make the milk a bit hotter!!!"

The Ideal Temperature Range for Milk Coffee

We know that whether it's a traditional latte or a trendy flat white, for most coffee shops, there's a recognized temperature range for milk frothing—55°C to 65°C. This is a moderate, palatable temperature. For beginners, their instructors often have higher requirements: to precisely control the milk frothing temperature at 65±3°C. The reason for such strict requirements is that at this temperature, the sweetness of milk becomes more pronounced. It makes the overall texture of the coffee richer, creates latte art patterns that last longer, and allows for better integration with coffee, resulting in a fine and delicate foam! Generally, the temperature of milk coffee doesn't exceed 68°C.

The Effects of Excessive Temperature

However, if you use milk foam above 70°C to make milk coffee, you'll find that: the foam doesn't create very attractive latte art. In terms of drinking experience, besides being scalding hot, this latte doesn't offer much sweetness. Moreover, you can clearly feel that the foam and coffee are in a separated state, not blended together, resulting in a very rough texture, and the foam dissipates much faster! The overall experience isn't very pleasant, which is why FrontStreet Coffee generally informs customers that the milk temperature can be higher, but not scalding~

(This image is not related to 70°C milk, just some less-than-perfect latte art from a friend of FrontStreet Coffee) Why does the experience worsen when the milk temperature is increased? The main reason lies in protein denaturation! Milk foam is primarily composed of proteins in milk and injected air. When we froth milk, as the temperature gradually increases, the two originally intertwined characteristics of proteins in milk gradually release, transforming into a form with one end hydrophobic and one end hydrophilic! The steam injected during frothing contains more moisture, so the hydrophobic end of proteins wraps around the injected air to avoid this added moisture, forming bubbles, while the outside of these bubbles is surrounded by a barrier formed by the hydrophilic end. This is how milk foam is formed.

The Science Behind Milk Foam Degradation

However, this milk foam is not "invincible"—it has certain weaknesses. When the milk temperature exceeds 70°C, proteins begin to denature or rapidly decompose, which directly causes the bubbles wrapped by proteins to burst and deteriorate. Moreover, this layer of foam will, after blending with coffee, directly create a "foam-coffee" separation due to the temperature difference, resulting in a very rough texture!

(Milk foam frothed to 71°C dissipates extremely quickly) As for sweetness, as FrontStreet Coffee mentioned, it's affected by temperature! The sweetness in milk comes from its lactose content. However, lactose doesn't have the same distinct sweetness as fructose. If we quantify the sweetness of sugars, sucrose would have a value of 1.0, while lactose only has 0.16! Although this seems low, interestingly, we can perceive different levels of lactose sweetness depending on the milk temperature!

Temperature and Sweetness Perception

Just like coffee, when a cup has acidic notes, we can only detect slight acidity at high temperatures, but as the temperature drops, the perception of acidity amplifies, resulting in a more pronounced sour taste experience. The range of 60°C to 70°C is when lactose sweetness is most apparent! FrontStreet Coffee specifically conducted an experiment, testing the sweet taste perception of milk at different temperatures, and the facts confirmed this to be true! Milk in this temperature range makes it easier to perceive sweetness compared to hot milk at other temperatures. However, when the milk temperature exceeds 70°C, our perception of lactose sweetness in milk significantly decreases, which is why it doesn't taste as sweet!

Irreversible Effects and Professional Standards

Furthermore, when milk is frothed above 70°C, these phenomena become irreversible negative conditions. This means that even if you wait for the temperature to drop to the normal range, this coffee won't taste as good as one made directly at the proper temperature because the proteins inside have already been damaged and cannot be repaired. Although the temperature has dropped, it still doesn't taste good! This is why beginners face more precise milk temperature requirements—so they can understand the不可逾越的 peak temperature for milk, thereby avoiding making unattractive and unpalatable milk coffee due to excessive temperature!

Practical Tips for Temperature Control

If you're worried about coffee cooling too quickly, we can indeed适当 increase the temperature, but not too much—68°C is already the peak! Besides this, we can also choose ceramic cups as serving vessels for milk coffee, as ceramic has certain heat preservation properties. Placing them on the coffee machine to heat up before use, or preheating them with hot water, can effectively slow down the cooling rate of milk~

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FrontStreet Coffee
10 Bao'an Qianjie, Yandun Road, Dongshankou, Yuexiu District, Guangzhou, Guangdong Province

Important Notice :

前街咖啡 FrontStreet Coffee has moved to new addredd:

FrontStreet Coffee Address: 315,Donghua East Road,GuangZhou

Tel:020 38364473