cappuccino with thick foam on top

How to Make Milk Foam (For Coffee)

A cappuccino wouldn’t be the drink it is without a foamy milk layer on top. The same goes for a latte, macchiato and many other fancy ‘coffee shop drinks’. It changes them from a simple cup of coffee into something just a little more special. But did you know there’s a lot of science (and art) behind these drinks?

For one thing, you can make these milk foams in two different ways: using steam or agitation. And some coffee experts will have very strong opinions on which one is ‘best’. But, regardless of the method you’re using, it’s all about controlling the conditions and knowing what type of milk foam you’re actually after. Whether that’s a thick and luscious foam for a dry cappuccino, or a light liquid microfoam to make beautiful latte art. In the end, it’s about controlling air bubbles through time, power, and temperature.

Step 1: Decide what type of milk foam you’re after

To complicate matters, there’s not just one type of milk foam. On one end of the spectrum, you will find thick, gloopy foams. You can’t pour them, instead, you’ll have to scoop the foam onto whatever it is you’re making. On the other extreme, you’ll find milk foams that might initially not even look like a foam. They’re still pretty liquid and can be poured easily. But, upon closer inspection, you’ll notice that they’re just a little thicker than pure milk.

There is no one ‘best’ foam, it all depends on your application. For instance, do you want to make latte art on top of your drink? That is, use milk to create a beautiful pattern on top of your drink. Or, do you just want a dollop of foam on top of your drink? You’ll need a thin liquid foam for the former and a thick pillowy foam for the latter. So, start by deciding what type of milk foam you’re after.

foaming milk with frother
Milk before (left) and after (right) being foamed up. Notice the large increase in volume. This final milk foam contains a lot of air. As a result, it is quite thick and won’t flow easily.

Step 2: Analyze your ideal foam

Next up, it’s time to have a closer look at that foam that you want to make. For simplicity’s sake, we’ll assume you’ll be using cow’s milk to do so. You can make foams from other types of milk, but their science is just a little different and we’ll discuss that in a separate article.

Milk foam is ‘aerated milk’. That is, it’s milk that contains a lot of air bubbles spread throughout. Foams are quite common in food – bread is a foam, so is the crema layer on top of your espresso, a meringue, as well as Dalgona coffee – but you can’t make a foam out of just anything. If you’ve ever tried to make a foam out of pure water, you’ll have experienced that for yourself. Pure water can’t hold onto air bubbles, no matter how hard you whisk it in.

Milk proteins stabilize air bubbles

Cow’s milk can form a foam because, alongside water, it contains ingredients that can hold onto air bubbles. Both the casein and whey proteins, the two most prevalent protein types in milk, help to stabilize the foam.

Proteins are long chains of which some sections prefer to sit in water (hydrophilic), and some do not (hydrophobic). As a result, they align themselves in such a way that the hydrophilic parts sit in water, whereas the hydrophobic parts sit in the air bubbles. They sit on the interface between water and air. This stabilizes the bubbles. They can’t move as easily, slowing down their escape.

Milk foams are liquid + foam

Proteins aren’t strong enough to hold onto air bubbles forever. Milk foams are notoriously unstable. Within a matter of 30 minutes, most milk foams made from pure milk have collapsed at least partially splitting into two phases. What’s more, many foams already exist of these two separate phases right after they’ve been made:

  • A liquid layer at the bottom: since air bubbles are lighter, they travel to the top, while the liquid sinks down
  • A foamy layer on top: the air decreases the density of the milk, it’s why a foam floats on top of a coffee so well

For many applications, you might not even be after 100% foam. You might want some light and fluffy foam, as well as some remaining more liquid milk. Do note though, that over time, you will always lose foam and increase the amount of liquid milk.

Smaller, more evenly sized air bubbles make more stable foams

Larger air bubbles escape from the milk more easily (which can be described by the laws of sedimentation). The same goes for bubbles with a wide variety in size. They merge together more easily than bubbles of the same size (a mechanism called Ostwald ripening).

Thicker, fluffier foams generally contain larger air bubbles. It’s simply harder to break them up into smaller pieces. As a result, these foams tend to be less stable. Thinner, more liquid foams can contain tiny, evenly sized air bubbles. These bubbles don’t escape as easily. As a result, these foams do tend to be a bit more stable.

Keep in mind that the final size distribution depends strongly on the method you use for making your foam, as we’ll discuss below.

More air makes a firmer milk foam

It is helpful to know whether your ideal milk foam contains a lot of air, or just a little bit. Thick, pillowy milk foams that need to be scooped contain a lot of air. When making a foam like this, the volume of milk will double, if not triple, in volume. As a result, the density of these foams is very low, giving them a light and airy drinking experience.

Milk foams that can still be poured on the other hand often contain a much smaller percentage of air. The milk doesn’t increase in volume that much when made into milk foam.

Micro- vs macrofoam

You may have heard of the term microfoam. This term is used to describe the foam that baristas use to make latte art. These foams contain quite a low amount of air, and the air is distributed throughout the milk in a lot of tiny air bubbles. As a matter of fact, you should barely be able to see the bubbles. These foams need to be glossy and smooth so they can be poured well. To make a good microfoam, you need to control both the total amount of air (not too much) as well as the air bubble size (pretty tiny). Making a good microfoam is a balancing act and when made by hand requires skill and experience.

Some may refer to macrofoams as being the opposite of a microfoam. However, this term is not as widely used, nor defined. Generally speaking, a macrofoam would contain more air and bigger bubbles, but it’s not as clear-cut.

Best stability for warm, but not hot, foam

Do you need a warm or a cold foam? Cold drinks work best with a cold foam, the shock would cause a hot foam to collapse more quickly. Warm drinks on the other hand do best with a warm foam.

You can make milk foam from both cold and warm milk. However, a warm milk foam is more stable. The heat helps the proteins unravel. This helps to further stabilize the foam. Generally speaking, the optimum temperature for a warm milk foam lies between 50-65°C (122-150°F). Higher temperatures will cause proteins to break down by a process called denaturation. Casein micelles especially may start to break down.

Making cold milk foam

You can also make foam from cold milk. Interestingly, it is easier to make a milk foam from cold milk, for instance milk from the fridge than it is to make milk foam from milk held at room temperature. This is due to the fat. At approximately room temperature, milk fat is partially solid, partially liquid, making it somehow best at destabilizing the foam.

Step 3: Choose the method to make your milk foam

To make a milk foam, you need to incorporate the right amount of air. And, you need to control the size of the air bubbles. When making milk foams for coffee, there are two commonly used ways to do so:

  1. Mechanical agitation: a fancy way of saying that you whisk or stir the milk to incorporate air bubbles
  2. Steam: inject hot steam + air into the milk.

Both methods have their pros and cons and different aspects that need to be controlled for making the ideal foam you’re looking for. That said, a skilled ‘milk foamer’ can make just about any type of foam using both methods. One may just be more suitable or easier than the other.

Stir or whisk to make a foam

Let’s look at the simplest method first: vigorously stirring or whisking milk to make a foam. This method is often referred to as ‘frothing milk’ The principle behind this method is quite simple. By quickly moving the milk about you’re trapping the surrounding air within. It’s comparable to whisking egg whites or cream into a foam.

While making a foam this way you agitate the proteins in the milk. Whey proteins especially are sensitive to this. As a result, they unravel. This makes it easier for them to align themselves on the water:air interface. There are a lot of ways you can use mechanical agitation to create a milk foam.

Simplest method: use a whisk or a bottle

Up first: making milk foam by hand, by whisking the milk with a whisk or shaking it in a closed container such as a mason jar or water bottle. Disadvantage: it’s a labor-intensive process. Also, in the case of whisking, it may be hard to properly whisk the relatively small amount of milk foam your need.

Generally speaking, both these methods make a milk foam with a lot of larger air bubbles. The shaking and whisking is not strong enough to break these larger bubbles into smaller ones. These large air bubbles make the foam more unstable and less delicate.

milk foam made with blender
Milk foam made with a stick blender. The top has formed a nice smooth foam. However, the bottom is still liquid.
(Stick) blender: works to an extent

Alternatively, you can use a (stick) blender to make milk foams. Blenders incorporate air by creating a vortex. The milk is swirled around and pulled back in in the middle, taking along air. In order for these to work well, you need enough milk, but also enough liquid milk to form that vortex. Once the foam starts forming this can prove to be challenging. When using an immersion blender, try to use a container with a small diameter for optimal success. Also, keep in mind that these methods will not warm up the milk for you. So, you will need to heat the milk in the microwave or on the stovetop on forehand.

Use a dedicated ‘frother’

One way to reliably whisk up some milk foam is by using a dedicated ‘frother’. Most of these contain an iron spun ring, a frothing coil, that serves as the whisk (see stirrer in the photo above). All you have to do is either move it up and down quickly by hand (like a French press), or electricity does the job for you and spins it around. In both cases, the design of the coil is such that it incorporates a lot of air bubbles. Some frothers are completely automated (such as the Philips one in the photo above) and don’t allow you to adjust any settings. With others you have some more freedom with regards to positioning the frothing coil, as well as timing.

Some frothers may be able to control the milk’s temperature as well. Some do so by heating the frothing coil itself. Since the milk quickly passes through the coil several times, it is an efficient way to redistribute heat. In other cases the surrounding encasing warms up the milk.

Control vs. consistency

When using mechanical agitation you may not have control over all the different parameters that influence your final foam’s consistency. You will want to be able to control temperature, amount of agitation and amount of air that’s incorporated. The more automated devices may give you less control, but make it easier to create a consistent product.

As an example, when you use a handheld frother, you can decide how how or high low you hold the frother to incorporate more or less air. However, that does require the skill and experience to know how much to incorporate. With a more automated system you can no longer control this, but, you probably do have a more consistent result.

Pushing steam through milk to make a foam

If you’ve seen a barista make milk foam, you’ve likely seen the steaming method at play. It’s widely used by baristas all over the world. They use a so-called ‘steam wand’ on their espresso machines to steam milk. When steaming milk, the steam wand injects steam into the milk. By controlling the positioning of the milk in the wand, air is pulled in as well.

The steam simultaneously heats up the milk and vigorously mixes the milk to create a vortex. This vortex is crucial because it ensures that all the added air bubbles are broken up and distributed throughout the foam evenly. The heat of the steam can denature proteins. This may help stabilize and form the foams. These denatured proteins are good at lying on the interface between water and air.

There is a range of different designs of nozzles for steaming milk. They may all entrap and inject air in a slightly different way, resulting in a slightly different foam.

Longer steam = hotter foam

By controlling the time they foam milk, baristas automatically control the temperature. Keep in mind that the steam coming in is very hot and quickly heats up the milk. Generally speaking, baristas aim for a steamed milk temperature of max. 65°C (150°F) at the end of steaming.

Higher pressure = firmer foam

The other major factor you can control with this method is the amount of pressure used. A higher pressure speeds up the formation of the foam. Generally speaking, these foams are also firmer and more stable. Whether that’s a good thing though depends on how you want to use the foam. For some applications, a thinner foam might be better for more delicate decorations.

Controlling air inflow

By lowering or lifting the jar of milk compared to the steam wand baristas can control the amount of air they incorporate into the air. Too much and you create a thick firm foam. Too little and the milk doesn’t get foamy at all. Using a steam wand requires some skill and experience to ensure the right amount of air gets incorporated.

Steam milk cannot make a cold foam

Whereas you can make a cold milk foam using mechnical agitation, you cannot do so using the steam method. It inherently makes a warm/hot foam since steam by itself it hot.

pouring milk in coffee
Pouring a very thin milk foam into a cup of coffee.

Steamed milk vs. frothed milk

You can make most warm milk foams using both steam as well as mechanical agitation. Generally speaking though, steaming is the preferred method for making a microfoam. It gives the milk foamer a lot of control over the method and it is relatively quick and easy. However, by adjusting factors such as time, temperature, speed, etc. you can make most foams with both methods. It depends strongly on the skill of the person using the tools.

Best cow’s milk to make milk foam

Choosing your preferred foaming method is crucial for making a milk foam. But, don’t underestimate the impact of the type of milk you’re using. Depending on what type of foam you’re looking for, a different type of milk may be your preferred choice. Again, here we’ll just focus on cow’s milk seeing as how the considerations will change when using plant-based versions.

Skimmed is more stable than full-fat

Fats can destabilize milk foams. The proteins that are supposed to stabilize the air bubbles, may instead surround the fat particles. As such generally speaking, milk foams made from skimmed milk are more stable than full-fat varieties. They’re slightly stronger as well. Full-fat milk on the other hand makes for a slightly creamier eating experience.

Which milk type is best for your application, depends on the requirements. If you’re after a thick, stable foam, skimmed is the way to go. If you’re after a thinner, creamier, consistency, full fat might work perfectly fine.

Pasteurized is stronger and more stable than UHT

Most milks have been heat treated before you’ll be using them for a milk foam. The heat treatment kills any pathogenic micro-organisms that might otherwise make people sick. It’s why pasteurization was invented. Nowadays, most milks have undergone one of three heat treatments:

  • Pasteurization: the mildest heat treatment – milk is held at approx. 72-75°C (161-167°F) for 15-30 seconds
  • UHT: heat treatment at 135°C (275°F) for just 2 seconds
  • Sterilization: milk held at 121°C (250°F) for approx. 15 min

The higher temperatures used for UHT and sterilized milk cause whey:casein aggregates to form. This will result in a more unstable foam.

Specially developed Barista milk

Milk manufacturers have discovered the milk foam market. They have developed milks that are ‘ideal’ for making a milk foam. You may think that all cow milks are alike, but manufacturers do have several levers they can pull to tweak the behavior of the milk.

Slight pH adjustment increases foam formation

By slightly lowering the pH-value of milk to a value of approx. 5.5, you can increase the amount of foam that can be made from milk. Slightly increasing the pH compared to its regular level can improve the stability of a milk foam.

pH-value is a measure for the acidity of a product. A lower value refers to a more acidic product. A higher value is more alkaline.

More intense heat treatment of milk powders makes more unstable foam

When making milk powder from liquid milk the milk receives some sort of heat treatment. The industry refers to these as low, medium and high heat treatment powders. Powders that have received a more intense heat treatment generally make less stable milk foams.

Higher protein:fat ratio makes more stable foam

Fats destabilize foams. Proteins stabilize foams. As a result, adding extra protein to milk or removing more fat can result in a more stable foam.

Interestingly, even the diet that a cow ate can impact the stability of a foam. Certain types of fats destabilize the foam more than others.

Homogenisation increases foam capacity

Most milks are homogenized during processing. During this process, the fat droplets in milk are broken down into smaller, more evenly sized droplets. Manufacturers can adjust the pressure used to do this. A higher pressure results in more foam formation, but slightly less stable foam as well.

All in all, there’s a lot that goes into making milk foam for your ideal drink. Next time you drink your cappuccino or latte, keep that in mind and maybe come up with a way to do it even better…


Augustin, M.A., Clarke, P.T. Skim milk powders with enhanced foaming and steam-frothing properties. Dairy Sci. Technol. 88, 149–161 (2008). link

Stefan Axelsson, Innovative Milk Foamer, Linkoping University, Master thesis, link

Goh, Jaclyn & Kravchuk, Olena & Deeth, Hilton. (2009). Comparison of mechanical agitation, steam injection and air bubbling for foaming milk of different types. Milchwissenschaft. 64. link

Jimenez-Junca, Carlos & Sher, Alexander & Gumy, Jean-Claude & Niranjan, Keshavan. (2015). Production of milk foams by steam injection: The effects of steam pressure and nozzle design. Journal of Food Engineering. 166. 10.1016/j.jfoodeng.2015.05.035. link

Klimanova, Yulia & Polzonetti, Valeria & Pucciarelli, Stefania & Perinelli, Diego & Bonacucina, Giulia & Cespi, Marco & Gabrielli, Maria & Santini, Giuseppe & Fioretti, Lauro & Cognigni, Luca & Vincenzetti, Silvia. (2022). Effect of steam frothing on milk microfoam: Chemical composition, texture, stability and organoleptic properties. International Dairy Journal. 135. 105476. 10.1016/j.idairyj.2022.105476. link

Madimutsa, Obert & Gwala, Wishmore & Mujuru, Felix & Nyambi, Clarice. (2017). Investigation of Factors Affecting Frothing Capacity of Pasteurised Whole Milk for Cappuccino Coffee. link

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