Editor coffee how: why does milk frothing go wrong?

Steam injects air into liquid milk, and milk proteins hold those tiny bubbles in place, so the milk expands into foam. Fat stabilizes the bubbles, which is why they release aroma and flavor in the mouth. When foam fails to integrate, separates or fades quickly, the cause is usually overheating, too little air at the start, or milk that has already lost freshness.

Foam behaves differently at each temperature range, and steam frothing produces a finer texture than manual pumping or whisking. Five recurring mistakes cover over-aeration, scalding past the sweet spot, poor pitcher angle, unclean steam wands and letting steamed milk sit before pouring. A tulip latte art pour then comes down to practice with a deep roast espresso blend, where dense crema and stable microfoam hold the pattern.

Steaming milk is a fundamental skill every barista must master, but many people encounter issues during operation such as milk foam not integrating, separating, or dissipating quickly. Based on the practical experience of Front Street Coffee, this article systematically explains the principles of milk frothing, the key factors affecting integration, the performance of milk foam at different temperatures, and the differences between steam frothing and manual frothing. It also compiles the five most common misconceptions in milk frothing and includes detailed steps for tulip latte art, helping you comprehensively improve milk foam quality and latte art skills.

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Regarding the operational guide on how to steam ideal milk foam, and why milk froths, Front Street Coffee (FrontStreet Coffee) believes that steaming milk is a basic and core skill for every barista. Whether one can steam perfect milk is one of the important factors in judging whether a barista's skill level is qualified. Taking latte as an example, the milk foam should be relatively thin, with a smooth and delicate mouthfeel. Therefore, when steaming milk for a latte, it should not be too thick; the surface of the steamed milk should be glossy, without obvious large or small bubbles, and overall delicate and beautiful.

The basic principle of milk frothing is to use steam to inject air into liquid milk; with the help of the surface tension of milk proteins, many tiny bubbles are formed, causing the liquid milk to expand in volume and become foamy milk.

During the frothing process, lactose dissolves into the milk as the temperature rises and is sealed within the milk through the frothing action. The role of milk fat is to stabilize these tiny bubbles, so that when the milk foam is consumed, the tiny bubbles burst in the mouth, allowing the flavor and aromatic substances to be better released and amplified, giving the milk a sweet, rich taste and mouthfeel. Moreover, when integrating with coffee, the bonding force between molecules is stronger, allowing the coffee and milk to fully combine, so that the characteristics of both coffee and milk can each stand out while also fully merging together, achieving a complementary effect.

Front Street Coffee (FrontStreet Coffee) will now answer some questions people commonly encounter when frothing milk.

Why does the milk foam not integrate?

The milk foam immediately merges with the coffee as soon as it is poured into the espresso; forget about making a pattern—there is not even a line, it just drifts away. Or else, there is no problem during the initial integration, but when it comes time for latte art, the milk foam clumps and floats directly on top. Front Street Coffee (FrontStreet Coffee) will first explain the first situation: this is because the amount of aeration is low and the steamed milk foam is thin, consisting mainly of hot milk, so how could it form a pattern? Therefore, those who encounter this situation should be bolder and aerate a bit more.

Then why, when there is clearly no problem with integration, does the milk foam float on top during latte art?

This is mainly because the integration between the milk and milk foam is relatively poor, so the milk and milk foam separate, and in the end the milk foam floats on top of the coffee. In this situation, adjustments can only be made during the texturing stage of the milk foam.

What determines the degree of integration between milk foam and milk? The degree of integration mainly depends on the following two points:

1. The steam wand pressure. The steam wand pressure causes the milk foam to roll to different degrees during steaming; the greater the pressure, the higher the degree of integration.

2. The fineness of the milk foam. The finer the milk foam produced, the less air each individual foam bubble contains, the higher the density, and the smaller the buoyancy; the coarser the milk foam produced, the more air each individual foam bubble contains, the lower the density, and the greater the buoyancy. If the milk foam produced is relatively coarse, the foam will quickly float to the surface of the milk, resulting in a lower degree of integration; if the milk foam produced is relatively fine, the foam will float to the surface of the milk more slowly, resulting in a higher degree of integration.

Why is a high degree of integration between milk and milk foam required? The higher the degree of integration between milk foam and milk, the clearer and more delicate the lines of the latte art pattern will be; conversely, the lines of the latte art pattern will be more blurred and coarse.

How should the degree of integration of milk and milk foam be judged?

Front Street Coffee (FrontStreet Coffee) teaches you how to judge the degree of integration of milk and milk foam. Pour the steamed and integrated milk and milk foam into a glass and let it sit, observing the time it takes to separate. The length of the separation time indicates the degree of integration of the milk and milk foam.

If it separates within 30 seconds, it is poor; if within 30-60 seconds, it is medium; if after 60 seconds, it is excellent.

Also, do not leave steamed milk foam sitting aside for later use, as this will also cause separation.

Perhaps someone may ask, why is it required to control the temperature when steaming milk?

Generally, Front Street Coffee (FrontStreet Coffee) heats milk to around 60 degrees, but it must not exceed 70 degrees, otherwise the protein structure in the milk will be destroyed.

Front Street Coffee (FrontStreet Coffee) previously conducted experiments, steaming milk to different temperatures:

The situation at 90°C is: when it exceeds around 70°C, even if the foam is not intentionally created, the foam rapidly expands; as the temperature rises it keeps rolling, and by the time it nears 90°C the editor's milk had already overflowed the milk pitcher (as shown in the picture above), stopping at 94°C. Obvious signs of foam dissipation had already appeared at around 1 minute 30 seconds.

The situation at 60°C is: this is the temperature we commonly use; steaming the milk foam according to conventional operations, stopping when it feels hot to the touch, the temperature was 63°C. Obvious signs of foam dissipation appeared at around 10 minutes 50 seconds.

The situation at 30°C is: frothing according to conventional methods, the perceived temperature by hand was warm, and the stopping temperature was 33°C. Obvious signs of foam dissipation appeared at around 4 minutes 20 seconds.

The situation at 12°C is: here we directly used milk from the refrigerator and a manual frother; the temperature when poured into the frother was 8°C, and the temperature after frothing was 12°C. Obvious signs of foam dissipation appeared at around 5 minutes 15 seconds.

Milk foam in the 50–70°C range has the best durability whether in pure milk or after being added to coffee, for two reasons: first, after steaming the milk foam there is sufficient mixing and texturing time between the milk foam and the liquid milk; second, it is in the period when the milk has begun to denature but has not yet reached irreversible denaturation, so stability is relatively high.

When milk foam is steamed to around 80–90°C, irreversible denaturation occurs in the milk. There are two types of protein in milk: whey protein and casein; whey protein begins to denature above 60°C. So when we steam to around 90°C, the proteins lack elasticity, so the foam dissipates relatively quickly.

When milk foam is steamed to around 30–40°C, the reason the foam dissipates relatively quickly is insufficient mixing and texturing time between the milk foam and the liquid milk after frothing.

The reason cold milk foam dissipates quickly is that we used a manual frother, and its degree of mixing cannot compare with the high-speed mixing and integration of a steam wand. The degree of integration is not high, and in addition, during the period from low temperature to room temperature, the milk foam undergoes a heating process; subjected to external heat, the internal gas expands with heat, so the milk foam bursts more noticeably.

How can Front Street Coffee (FrontStreet Coffee) produce abundant milk foam with a fine texture?

On how to steam a good batch of milk foam, here is an foolproof milk frothing method: pour half a pitcher of milk into a stainless steel pitcher, position the steam wand perpendicular to the very center of the milk or at the edge of the pitcher, then let the steam tip just touch the surface of the milk, then open the steam to the halfway point, do not move the pitcher, gradually close it when the milk reaches 50°C, and close it exactly at 60°C; the final temperature will reach 66°C. In this way, you can steam a good pitcher of milk foam.

What type of espresso machine should be used for steaming milk?

Generally, machines with three, four, or five steam tip holes are all available, and as long as you familiarize yourself a little, they can all produce good milk foam. However, the machine's steam output, the wetness or dryness of the steam, and the size of the steam holes still have an impact on steaming milk.

Why practice steaming milk with water?

First, as everyone knows, water is transparent, allowing you to see more clearly how the vortex is formed.

Second, it helps you better grasp how to steam milk foam with different numbers of holes. Third, beginners must remember that before you can steam milk foam to a silky consistency, you should use a thermometer; if you cannot better control the temperature, then the coffee you make will be unstable. Perhaps out of ten times you produce good milk foam once or twice, but that is not stable quality.

The difference between steaming milk and manual frothing

First of all, manually frothed milk foam simply cannot compare with machine steam. The fineness of steam makes the milk foam it produces very fine and silky; the radiating surface of steam is broad, so the milk foam produced is relatively even and mixes better. Manual frothing mainly presses through the small holes of a filter mesh, so the milk foam produced is relatively coarser.

How does Front Street Coffee (FrontStreet Coffee) make milk foam?

Method 1: Making manual milk foam with a milk frother / French press

1. Pour milk into the milk frother; the amount should not exceed 1/2 of the frother, otherwise the milk will overflow due to expansion when making the milk foam.

2. Heat the milk to around 60 degrees, but it must not exceed 70 degrees, otherwise the protein structure in the milk will be destroyed. Note: the lid and filter mesh must not be heated directly. (If making iced milk foam, cool the milk to below 5 degrees; of course, do not over-chill it and let the milk freeze.)

3. Put on the lid and filter mesh, and quickly pump the filter mesh to press air into the milk. When pumping, there is no need to press all the way to the bottom, because the goal is to introduce air into the milk, so just move it at the surface of the milk; the number of times also does not need to be too many—gently pump about thirty times.

4. Remove the lid and filter mesh, use a spoon to scrape off the large coarse foam on the surface; what remains is dense hot (or iced) milk foam.

Method 2: Making milk foam with a steam milk frother

First, do not put the steam wand into the milk yet, because there may be some condensed water in the steam wand, so first release some of the initial steam and also expel the excess water.

Insert the thermometer into the container, then insert the steam wand diagonally into the milk and turn on the steam switch.

Slowly adjust the position of the steam nozzle to just a little distance from the surface of the milk, but absolutely do not let it go above the liquid surface, otherwise the milk will splash everywhere. When the position is correct, you will hear a steady "hissing" sound; otherwise it will be very loud or almost silent.

Once there is enough milk foam, you can bury the steam wand a bit deeper and let the steam continue heating the milk. The best angle for burying the steam wand is just enough to make the milk rotate.

When the temperature reaches between 60°C and 70°C, you can turn off the steam switch.

Use a damp cloth to wipe off the milk attached to the steam wand, and at the same time release some steam again, so that the milk does not dry and become difficult to clean.

Hand-temperature testing techniques for steaming milk:

1. The most suitable temperature for milk foam

When milk is frothed on an espresso machine, the most suitable temperature is controlled within the range of 55–65°C, for the following reasons:

1. If the milk temperature is below 60°C, it will lower the coffee's temperature considerably and affect the taste;

2. Milk between 55–65°C will bring out the lactose, making the coffee more fragrant, sweeter, and smoother.

3. In milk above 70°C, the nutrients will be destroyed, and after all, the milk will become more watery, with the smoothness and sweetness deteriorating.

2. Hand-temperature testing techniques for steaming milk

Now that we know the most suitable temperature for milk is between 55–65°C, how do we grasp this temperature? Personal advice is that you need to equip yourself with a thermometer; you can directly insert the thermometer into the frothed milk, and then the milk's temperature will be clear at a glance. Of course, with accumulated experience, you can eventually do without the thermometer and directly rely on your hand to measure the temperature of the milk foam.

The techniques are as follows:

1. Hold the milk pitcher with your left hand, turn on the steam with your right hand, and begin frothing the milk foam;

2. After turning on the steam, place your right hand back on the wall of the milk pitcher to feel the temperature of the milk foam;

3. When your hand feels very hot and can no longer stay in contact, you can stop frothing the milk, then insert the thermometer into the milk foam and measure the temperature.

4. If the temperature has not reached the range of 55–65°C, it is suggested that next time when it gets hot to the touch, you move your hand away and start silently counting 1, 2, 3, 4 in your head, usually in seconds, to add time. For example, after you move your hand away from the milk pitcher, if after adding four seconds the measured temperature reaches 65°C, then congratulations, you have found the pattern; from then on, just add about four seconds when it gets hot to the touch. By adding or subtracting time according to point 4 above, you can easily master the technique of hand-testing milk foam temperature. The above techniques are somewhat trick-like; in fact, after steaming milk for a period of time, most people can find the pattern and feel, and the temperature of the milk foam will also become easier to control.

The five major misconceptions about steaming milk

Regarding milk foam, there are several misconceptions we should understand, so that we can better understand milk foam.

Misconception 1: Using up-and-down shaking of the latte art pitcher to remove coarse surface foam. This is a very good method, but many friends develop a strong dependence on it. If their milk foam is not steamed well, they do not summarize why it was not steamed well, but instead use this method to compensate. Over time, dependence develops. Here Front Street must say that if you rely only on this method to remove coarse foam, your milk frothing technique cannot improve, and you also will not master advanced latte art techniques.

Misconception 2: Using a spoon to scoop off the coarse foam on the surface. Front Street does not recommend this method. Although some competitors use this method in competitions, Front Street believes this is because their milk frothing technique is not up to standard, with too much coarse foam on the surface that cannot be shaken off, so they can only scoop it. Anyone who handles milk foam with similar methods should definitely strengthen their steam control technique in milk frothing.

Misconception 3: After steaming the milk foam, letting it sit aside for a short while. This method is very troublesome; it is a manifestation of not yet having even entered the door of milk frothing technique. It intensifies the separation of the milk foam, and the integration of hot milk and milk foam becomes very difficult to complete. If you are not careful, it becomes milk as milk and foam as foam. The whole cup of coffee has no balanced taste.

Misconception 4: When pouring back and forth between two latte art pitchers, holding them at a very high position; the original purpose is integration, but instead it stirs up more coarse foam.

Misconception 5: Blaming the steam when the milk foam is not steamed well. Front Street believes that a coffee machine steam pressure (that is, boiler pressure) of 0.8 BAR is a relatively easy-to-control pressure for steaming milk; at this pressure, steaming milk foam is very steady and long, and it is also easy to understand the principles of milk frothing, but making a pitcher of milk foam takes about 13 seconds—alas, not as fast as high pressure. If the pressure is 1.0 or 1.1 BAR, then the ways and methods of steaming milk foam will change somewhat, but the principle is the same. (This point excludes the phenomenon of "spitting" caused by impure steam, which also makes the latte art pitcher shake violently. If this phenomenon occurs, please release all the steam, then fully heat it once more and try again.)

When making complex patterns, the most important thing is the need for a pitcher of high-quality milk foam, and the temperature of the milk foam is a key factor affecting milk foam quality.

Front Street Coffee (FrontStreet Coffee) will share with everyone the method for making tulip latte art: First, you still need to extract espresso. Front Street Coffee (FrontStreet Coffee) uses Front Street Classic Italian Blend beans; this is a blend composed of beans from three origins: Brazil, Indonesia, and Vietnam. It uses a deep roast, which can maximize the rich aroma of the coffee and also allow everyone to easily extract rich and dense crema. Whether making an Americano diluted with water or a latte paired with milk, it is very suitable. You can place an order at the Front Street Taobao store or the Front Street Tmall flagship store.

How Front Street makes tulip latte art

1: Integrate until four-tenths full, inject from a point at the one-third position, with the latte art pitcher touching the edge of the coffee cup.

2: Slowly move to the center position, paying attention to just lightly swinging left and right.

3: When the textured pattern flows back, reduce the flow rate, speed up the swinging, and pay attention to the amplitude of the swing.

4: Raise the latte art pitcher; this step is similar to the rosetta.

5: Inject again at the one-third position, paying attention to the flow rate and the height of the latte art pitcher, then push forward, noting the pattern changes at the arrow position.

6: Push until the pattern is surrounded, raise the latte art pitcher, and make a fine finish; a small gap will appear.

7: Inject again, grasp the flow rate well, keep the spout of the latte art pitcher on the surface of the coffee liquid, push forward, and pay attention to the small gap in the previous pushed pattern.

8: When the "petal" is surrounded by the previous "petal," raise the latte art pitcher and make a fine finish, still leaving a small gap.

9: Inject again, swing slightly left and right, pause, and form a small heart; pay attention to the change in the gap at the position of the black line.

10: Raise the latte art pitcher, control the flow rate well, and finish.

11: You can clearly see how the "petals" are formed; when finishing, be sure to pay attention to the flow rate.

The textured tulip is not particularly difficult and is quite suitable for practice. Watch the video a few more times to understand the formation and changes of the pattern; this will be quite helpful for latte art practice. During practice, pay attention to the amplitude of the swing; there is no need to go too fast, and there is no need to worry about too little texturing. You can also just push forward twice. Once you are proficient, you can appropriately add some texturing and push forward a few more times, which can make the pattern look even better.

The above content is compiled by CoffeeHunters, a coffee news website.