A cappuccino wouldn’t be the drink it’s with out a foamy milk layer on high. The identical goes for a latte, macchiato and plenty of different fancy ‘espresso store drinks’. It adjustments them from a easy cup of espresso into one thing just a bit extra particular. However do you know there’s a whole lot of science (and artwork) behind these drinks?

For one factor, you can also make these milk foams in two alternative ways: utilizing steam or agitation. And a few espresso specialists may have very sturdy opinions on which one is ‘finest’. However, whatever the methodology you’re utilizing, it’s all about controlling the situations and figuring out what sort of milk foam you’re really after. Whether or not that’s a thick and luscious foam for a dry cappuccino, or a lightweight liquid microfoam to make stunning latte artwork. Ultimately, it’s about controlling air bubbles by way of time, energy, and temperature.

Step 1: Resolve what sort of milk foam you’re after

To complicate issues, there’s not only one sort of milk foam. On one finish of the spectrum, you will discover thick, gloopy foams. You may’t pour them, as a substitute, you’ll need to scoop the froth onto no matter it’s you’re making. On the opposite excessive, you’ll discover milk foams that may initially not even appear like a foam. They’re nonetheless fairly liquid and might be poured simply. However, upon nearer inspection, you’ll discover that they’re just a bit thicker than pure milk.

There isn’t any one ‘finest’ foam, all of it depends upon your software. As an example, do you wish to make latte artwork on high of your drink? That’s, use milk to create an attractive sample on high of your drink. Or, do you simply desire a dollop of froth on high of your drink? You’ll want a skinny liquid foam for the previous and a thick pillowy foam for the latter. So, begin by deciding what sort of milk foam you’re after.

Step 2: Analyze your preferrred foam

Subsequent up, it’s time to have a more in-depth have a look at that foam that you just wish to make. For simplicity’s sake, we’ll assume you’ll be utilizing cow’s milk to take action. You can also make foams from different kinds of milk, however their science is just a bit totally different and we’ll focus on that in a separate article.

Milk foam is ‘aerated milk’. That’s, it’s milk that accommodates a whole lot of air bubbles unfold all through. Foams are fairly widespread in meals – bread is a foam, so is the crema layer on high of your espresso, a meringue, in addition to Dalgona espresso – however you’ll be able to’t make a foam out of simply something. When you’ve ever tried to make a foam out of pure water, you’ll have skilled that for your self. Pure water can’t maintain onto air bubbles, irrespective of how laborious you whisk it in.

Milk proteins stabilize air bubbles

Cow’s milk can kind a foam as a result of, alongside water, it accommodates components that may maintain onto air bubbles. Each the casein and whey proteins, the 2 most prevalent protein sorts in milk, assist to stabilize the froth.

Proteins are lengthy chains of which some sections desire to sit down in water (hydrophilic), and a few don’t (hydrophobic). Consequently, they align themselves in such a means that the hydrophilic components sit in water, whereas the hydrophobic components sit within the air bubbles. They sit on the interface between water and air. This stabilizes the bubbles. They will’t transfer as simply, slowing down their escape.

Milk foams are liquid + foam

Proteins aren’t sturdy sufficient to carry onto air bubbles eternally. Milk foams are notoriously unstable. Inside a matter of half-hour, most milk foams created from pure milk have collapsed at the very least partially splitting into two phases. What’s extra, many foams exist already of those two separate phases proper after they’ve been made:

A liquid layer on the backside: since air bubbles are lighter, they journey to the highest, whereas the liquid sinks down
A foamy layer on high: the air decreases the density of the milk, it’s why a foam floats on high of a espresso so nicely

For a lot of functions, you won’t even be after 100% foam. You may want some mild and fluffy foam, in addition to some remaining extra liquid milk. Do notice although, that over time, you’ll at all times lose foam and improve the quantity of liquid milk.

Smaller, extra evenly sized air bubbles make extra steady foams

Bigger air bubbles escape from the milk extra simply (which might be described by the legal guidelines of sedimentation). The identical goes for bubbles with all kinds in dimension. They merge collectively extra simply than bubbles of the identical dimension (a mechanism referred to as Ostwald ripening).

Thicker, fluffier foams usually comprise bigger air bubbles. It’s merely more durable to interrupt them up into smaller items. Consequently, these foams are usually much less steady. Thinner, extra liquid foams can comprise tiny, evenly sized air bubbles. These bubbles don’t escape as simply. Consequently, these foams do are usually a bit extra steady.

Remember the fact that the ultimate dimension distribution relies upon strongly on the tactic you employ for making your foam, as we’ll focus on under.

Extra air makes a firmer milk foam

It’s useful to know whether or not your preferrred milk foam accommodates a whole lot of air, or just a bit bit. Thick, pillowy milk foams that should be scooped comprise a whole lot of air. When making a foam like this, the amount of milk will double, if not triple, in quantity. Consequently, the density of those foams could be very low, giving them a lightweight and ethereal consuming expertise.

Milk foams that may nonetheless be poured however typically comprise a a lot smaller proportion of air. The milk doesn’t improve in quantity that a lot when made into milk foam.

Micro- vs macrofoam

You could have heard of the time period microfoam. This time period is used to explain the froth that baristas use to make latte artwork. These foams comprise fairly a low quantity of air, and the air is distributed all through the milk in a whole lot of tiny air bubbles. As a matter of truth, you must barely be capable to see the bubbles. These foams should be shiny and clean to allow them to be poured nicely. To make a superb microfoam, it’s good to management each the whole quantity of air (not an excessive amount of) in addition to the air bubble dimension (fairly tiny). Making a superb microfoam is a balancing act and when made by hand requires talent and expertise.

Some could discuss with macrofoams as being the alternative of a microfoam. Nevertheless, this time period is just not as extensively used, nor outlined. Usually talking, a macrofoam would comprise extra air and larger bubbles, nevertheless it’s not as clear-cut.

Finest stability for heat, however not scorching, foam

Do you want a heat or a chilly foam? Chilly drinks work finest with a chilly foam, the shock would trigger a scorching foam to break down extra shortly. Heat drinks however do finest with a heat foam.

You can also make milk foam from each chilly and heat milk. Nevertheless, a heat milk foam is extra steady. The warmth helps the proteins unravel. This helps to additional stabilize the froth. Usually talking, the optimum temperature for a heat milk foam lies between 50-65°C (122-150°F). Greater temperatures will trigger proteins to interrupt down by a course of referred to as denaturation. Casein micelles particularly could begin to break down.

Making chilly milk foam

You can even make foam from chilly milk. Curiously, it’s simpler to make a milk foam from chilly milk, as an example milk from the fridge than it’s to make milk foam from milk held at room temperature. That is because of the fats. At roughly room temperature, milk fats is partially strong, partially liquid, making it someway finest at destabilizing the froth.

Step 3: Select the tactic to make your milk foam

To make a milk foam, it’s good to incorporate the correct quantity of air. And, it’s good to management the dimensions of the air bubbles. When making milk foams for espresso, there are two generally used methods to take action:

Mechanical agitation: a flowery means of claiming that you just whisk or stir the milk to include air bubbles
Steam: inject scorching steam + air into the milk.

Each strategies have their execs and cons and totally different elements that should be managed for making the best foam you’re on the lookout for. That mentioned, a talented ‘milk foamer’ could make nearly any sort of froth utilizing each strategies. One may be extra appropriate or simpler than the opposite.

Stir or whisk to make a foam

Let’s have a look at the best methodology first: vigorously stirring or whisking milk to make a foam. This methodology is sometimes called ‘frothing milk’ The precept behind this methodology is kind of easy. By shortly shifting the milk about you’re trapping the encompassing air inside. It’s similar to whisking egg whites or cream right into a foam.

Whereas making a foam this manner you agitate the proteins within the milk. Whey proteins particularly are delicate to this. Consequently, they unravel. This makes it simpler for them to align themselves on the water:air interface. There are a whole lot of methods you should utilize mechanical agitation to create a milk foam.

Easiest methodology: 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 comparable to a mason jar or water bottle. Drawback: it’s a labor-intensive course of. Additionally, within the case of whisking, it could be laborious to correctly whisk the comparatively small quantity of milk foam your want.

Usually talking, each these strategies make a milk foam with a whole lot of bigger air bubbles. The shaking and whisking is just not sturdy sufficient to interrupt these bigger bubbles into smaller ones. These massive air bubbles make the froth extra unstable and fewer delicate.

(Stick) blender: works to an extent

Alternatively, you should utilize a (stick) blender to make milk foams. Blenders incorporate air by making a vortex. The milk is swirled round and pulled again in within the center, taking alongside air. To ensure that these to work nicely, you want sufficient milk, but additionally sufficient liquid milk to kind that vortex. As soon as the froth begins forming this may show to be difficult. When utilizing an immersion blender, attempt to use a container with a small diameter for optimum success. Additionally, take into account that these strategies is not going to heat up the milk for you. So, you have to to warmth the milk within the microwave or on the stovetop on forehand.

Use a devoted ‘frother’

One strategy to reliably whisk up some milk foam is by utilizing a devoted ‘frother’. Most of those comprise an iron spun ring, a frothing coil, that serves because the whisk (see stirrer within the photograph above). All you must do is both transfer it up and down shortly by hand (like a French press), or electrical energy does the job for you and spins it round. In each instances, the design of the coil is such that it incorporates a whole lot of air bubbles. Some frothers are fully automated (such because the Philips one within the photograph above) and don’t let you alter any settings. With others you’ve some extra freedom almost about positioning the frothing coil, in addition to timing.

Some frothers might be able to management the milk’s temperature as nicely. Some accomplish that by heating the frothing coil itself. Because the milk shortly passes by way of the coil a number of instances, it’s an environment friendly strategy to redistribute warmth. In different instances the encompassing encasing warms up the milk.

Management vs. consistency

When utilizing mechanical agitation you could not have management over all of the totally different parameters that affect your ultimate foam’s consistency. You will have to have the ability to management temperature, quantity of agitation and quantity of air that’s integrated. The extra automated units could provide you with much less management, however make it simpler to create a constant product.

For instance, whenever you use a handheld frother, you’ll be able to resolve how how or excessive low you maintain the frother to include kind of air. Nevertheless, that does require the talent and expertise to know the way a lot to include. With a extra automated system you’ll be able to not management this, however, you in all probability do have a extra constant end result.

Pushing steam by way of milk to make a foam

When you’ve seen a barista make milk foam, you’ve seemingly seen the steaming methodology at play. It’s extensively utilized by baristas everywhere in 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 within the wand, air is pulled in as nicely.

The steam concurrently heats up the milk and vigorously mixes the milk to create a vortex. This vortex is essential as a result of it ensures that each one the added air bubbles are damaged up and distributed all through the froth evenly. The warmth of the steam can denature proteins. This may occasionally assist stabilize and kind the foams. These denatured proteins are good at mendacity on the interface between water and air.

There’s a vary of various designs of nozzles for steaming milk. They could all entrap and inject air in a barely totally different means, leading to a barely totally different foam.

Longer steam = hotter foam

By controlling the time they foam milk, baristas routinely management the temperature. Remember the fact that the steam coming in could be very scorching and shortly heats up the milk. Usually talking, baristas goal for a steamed milk temperature of max. 65°C (150°F) on the finish of steaming.

Greater strain = firmer foam

The opposite main issue you’ll be able to management with this methodology is the quantity of strain used. A better strain quickens the formation of the froth. Usually talking, these foams are additionally firmer and extra steady. Whether or not that’s a superb factor although depends upon the way you wish to use the froth. For some functions, a thinner foam is likely to be higher for extra delicate decorations.

Controlling air influx

By decreasing or lifting the jar of milk in comparison with the steam wand baristas can management the quantity of air they incorporate into the air. An excessive amount of and also you create a thick agency foam. Too little and the milk doesn’t get foamy in any respect. Utilizing a steam wand requires some talent and expertise to make sure the correct quantity of air will get integrated.

Steam milk can’t make a chilly foam

Whereas you can also make a chilly milk foam utilizing mechnical agitation, you can’t accomplish that utilizing the steam methodology. It inherently makes a heat/scorching foam since steam by itself it scorching.

Steamed milk vs. frothed milk

You can also make most heat milk foams utilizing each steam in addition to mechanical agitation. Usually talking although, steaming is the popular methodology for making a microfoam. It provides the milk foamer a whole lot of management over the tactic and it’s comparatively fast and simple. Nevertheless, by adjusting elements comparable to time, temperature, velocity, and so forth. you can also make most foams with each strategies. It relies upon strongly on the talent of the particular person utilizing the instruments.

Finest cow’s milk to make milk foam

Selecting your most popular foaming methodology is essential for making a milk foam. However, don’t underestimate the influence of the kind of milk you’re utilizing. Relying on what sort of froth you’re on the lookout for, a distinct sort of milk could also be your most popular alternative. Once more, right here we’ll simply deal with cow’s milk seeing as how the concerns will change when utilizing plant-based variations.

Skimmed is extra steady than full-fat

Fat can destabilize milk foams. The proteins which are alleged to stabilize the air bubbles, could as a substitute encompass the fats particles. As such usually talking, milk foams created from skimmed milk are extra steady than full-fat varieties. They’re barely stronger as nicely. Full-fat milk however makes for a barely creamier consuming expertise.

Which milk sort is finest to your software, depends upon the necessities. When you’re after a thick, steady foam, skimmed is the way in which to go. When you’re after a thinner, creamier, consistency, full fats may work completely positive.

Pasteurized is stronger and extra steady than UHT

Most milks have been warmth handled earlier than you’ll be utilizing them for a milk foam. The warmth therapy kills any pathogenic micro-organisms that may in any other case make individuals sick. It’s why pasteurization was invented. These days, most milks have undergone one in every of three warmth remedies:

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

The upper temperatures used for UHT and sterilized milk trigger whey:casein aggregates to kind. It will lead to a extra unstable foam.

Specifically developed Barista milk

Milk producers have found the milk foam market. They’ve developed milks which are ‘preferrred’ for making a milk foam. You could assume that each one cow milks are alike, however producers do have a number of levers they will pull to tweak the habits of the milk.

Slight pH adjustment will increase foam formation

By barely decreasing the pH-value of milk to a worth of approx. 5.5, you’ll be able to improve the quantity of froth that may be created from milk. Barely rising the pH in comparison with its common stage can enhance the steadiness of a milk foam.

pH-value is a measure for the acidity of a product. A decrease worth refers to a extra acidic product. A better worth is extra alkaline.

Extra intense warmth therapy of milk powders makes extra unstable foam

When making milk powder from liquid milk the milk receives some kind of warmth therapy. The trade refers to those as low, medium and excessive warmth therapy powders. Powders which have acquired a extra intense warmth therapy usually make much less steady milk foams.

Greater protein:fats ratio makes extra steady foam

Fat destabilize foams. Proteins stabilize foams. Consequently, including additional protein to take advantage of or eradicating extra fats can lead to a extra steady foam.

Curiously, even the eating regimen {that a} cow ate can influence the steadiness of a foam. Sure kinds of fat destabilize the froth greater than others.

Homogenisation will increase foam capability

Most milks are homogenized throughout processing. Throughout this course of, the fats droplets in milk are damaged down into smaller, extra evenly sized droplets. Producers can alter the strain used to do that. A better strain ends in extra foam formation, however barely much less steady foam as nicely.

All in all, there’s lots that goes into making milk foam to your preferrred drink. Subsequent time you drink your cappuccino or latte, hold that in thoughts and possibly provide you with a strategy to do it even higher…

References

Augustin, M.A., Clarke, P.T. Skim milk powders with enhanced foaming and steam-frothing properties. Dairy Sci. Technol. 88, 149–161 (2008). https://doi.org/10.1051/dst:2007012 hyperlink

Stefan Axelsson, Modern Milk Foamer, Linkoping College, Grasp thesis, hyperlink

Goh, Jaclyn & Kravchuk, Olena & Deeth, Hilton. (2009). Comparability of mechanical agitation, steam injection and air effervescent for foaming milk of various sorts. Milchwissenschaft. 64. hyperlink

Jimenez-Junca, Carlos & Sher, Alexander & Gumy, Jean-Claude & Niranjan, Keshavan. (2015). Manufacturing of milk foams by steam injection: The consequences of steam strain and nozzle design. Journal of Meals Engineering. 166. 10.1016/j.jfoodeng.2015.05.035. hyperlink

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

Madimutsa, Obert & Gwala, Wishmore & Mujuru, Felix & Nyambi, Clarice. (2017). Investigation of Elements Affecting Frothing Capability of Pasteurised Complete Milk for Cappuccino Espresso. hyperlink

YouTube movies: