Latte Foam

James Harper

So, a few months back, my girlfriend came to visit me while I was at my parents, in a small Italian town, and I was really curious to show her like, hey I actually spent a number of years growing up in and around here.

So we walked down the mountain road and came into the piazza.

And it is all the stereotypes.

On the left, massive catholic church.

In front, clock tower leading up to a castle.

And on the right is Bar Roma, the town's busiest cafe, with the usual huddle of like, elderly Italians gossiping weekly news.

And we ordered some cappuccinos.

And what landed in front of me was a cup with a mountain of white foam, kind of like whipped cream, with a dusting of cocoa on top.

And my nose plunged itself into the froth as I tried taking a sip.

And it tasted kind of raspy, papery in my mouth.

And to be honest, I was really kind of disappointed.

Because I knew how good it could be.

Toby Weedon

I've got the seam on just off to the side, just below the surface.

And I'm going to turn it on full power and away we go.

James Harper

So this is Toby Weedy, a business development manager for Oatly, the creators of the oat-based milk alternative drink, which you can make lattes from, and also the sponsor for this episode.

Toby explained to me that that raspy, papery foam I tasted in that Italian bar was a dry foam cappuccino.

Toby Weedon

Dry foam usually is much thicker and more sturdy.

And you can really like pick it up with a spoon and it sits in your mouth.

You can hold it in your mouth.

And the way that the drink is made, often by spooning the milk from the pitcher on top of the drink, you don't get any real combination of coffee with the foam.

James Harper

Now, back in that small Italian town, what I wish I had had instead was a microfoam cappuccino.

The kind of foam you would find in a specialty coffee bar.

Now, another term for a microfoam cappuccino is also a wet foam cappuccino.

And it's also called wet foam because if you swirl it around in a metal pitcher, it almost looks like ordinary milk, except for the fact that it's full of tiny, tiny bubbles.

Toby Weedon

And when a barista pours it, you're incorporating some of the coffee or some of the crema into the foam.

So you do get a combination then of the coffee and the foam.

James Harper

And to create really impressive latte art, you need microfoam.

Can't do it with dry foam.

But for me, most importantly, when you put it to your lips, it is sublime.

Toby Weedon

Because it is kind of really soft and velvety and delicate, it creates a really nice sensation within the mouth.

James Harper

Now, the difference between that dry foam cappuccino I had in Italy and the microfoam cappuccinos I enjoy in a Berlin specialty coffee bar, the difference really just comes down to the size of the bubbles.

And practically speaking, that is just a reflection of how much air a barista has incorporated into the Oatly or milk.

Toby Weedon

To create dry foam, you need to bring more air in at the beginning.

Whereas for wet foam, you bring a lot less air into the liquid at the beginning.

James Harper

Now, let's do some blue sky thinking.

How many lattes are made every day in every corner of the world?

Tens of millions?

No, surely not.

Hundreds of millions?

Billions?

Whatever it is, it's a lot.

But the thing is, most of them are going to be dry foam lattes.

Papery, raspy experiences.

Which, you know, is such a shame.

Because just imagine how much more luxurious those billions of latte sips could be if they were made with microfoam.

And this is why the topic of latte foam matters to me.

Because I want people to have more luxurious coffee experiences.

I want people to fall in love with coffee faster.

And when they fall in love with a quality coffee, you know, a microfoamed latte, over time, I expect they'll start paying more for quality lattes.

And this could be one of the keys to make the specialty coffee industry more financially sustainable.

So, in this episode, I'm going to take you into the world of latte foam and show you the microscopic processes that make it and destroy it.

Surfactants, proteins, fats, entrainment, draining, and so much more.

These are the things that ultimately affect what your cappuccino looks like and how it feels in your mouth.

And along the way, I'm going to take you into the original Oatly factory to show you how Oatly is made.

And at the end of the episode, I'm going to give you a clue as to what you can do in your bar or your kitchen to make latte foams which are even more luxurious, create even better latte art, and last even longer.

So, to kick us off on this foaming journey, allow me to introduce to you a scientist.

Prof. Steven Abbott

I'm Professor Steven Abbott.

So, I'm interested in why things stick, so adhesion, why things clean, so that's to do with surfactants, why things dissolve, that's to do with solubility.

And in the midst of all that, I was forced to learn the science of foams, which is one of the reasons we're having our discussion now.

James Harper

Now, to make latte foam, you gotta spill some milk.

And technically speaking, what I just said was incorrect.

I said, to create latte foam, you have to steam milk.

And while it is true that steam does enter the milk, it's kind of missing the bigger picture.

Prof. Steven Abbott

We all say it is steam, but the first thing that steam will do when it's anything less than 100 degrees centigrade is condense into water.

James Harper

So, when we quote unquote steam milk, what's happening is steam is quickly condensing into water.

But even that is beside the point, because the thing is, latte foam is not made from droplets of water.

It is made from air bubbles.

Prof. Steven Abbott

You cannot get a foam from condensed water, so it has to be air going in.

So, the foam has to be an air foam.

You haven't got a steam foam.

So, these wands, the steam wands attached to an espresso machine, are injecting steam to do the heating, but they are also entraining.

The force of the steam coming down entrains air.

James Harper

Oh, I see.

And the air comes from like, you know, it comes from in the room, really.

So, what it's doing is sucking in the air from the room and pushing it into the milk.

Prof. Steven Abbott

Let me give you a strange example.

You're on a plane and you have to jump out of the plane in an emergency and blow up your life jacket.

There is not enough air stored in that life jacket to inflate it.

So, the high-pressure gas which is released goes through a special nozzle which entrains a lot of air from outside.

So, most of the air in your life jacket comes not from the tiny bottle of high-pressure air, but from the air outside.

So, this is a universal principle of entrainment.

A small amount of original air brings a lot.

James Harper

So, if you want to be particularly unpopular with your local barista, when you ask them what they're doing while they're steaming milk and they reply, steaming milk, you say, no, you're not.

You're entraining air into the milk.

Like I said, a surefire way to make you unpopular.

So, lots of air is now being entrained into our milk.

But how does foam begin to form?

Prof. Steven Abbott

The energy from that steam wand must break up any big bubbles into small bubbles.

So, in the very first seconds of entraining air into the milk, you first of all get a kugelschaum, which is just the German for a ball of foam, because you just have individual bubbles of air.

James Harper

Remember those glorious days back when you were a kid and you stuck a straw into your milk sundae and you blew some bubbles into it?

And all these bubbles would start building on top of your sundae.

That is a kugelschaum.

But you can't make latte art with those sorts of bubbles.

However, when you're trying to make microfoam, after those first few seconds where you've incorporated a lot of air, you then stop incorporating as much air and you swirl it very aggressively.

This is the point, if you've done it right, it should be more quiet.

Prof. Steven Abbott

And this is why steaming your milk this way creates microfoam.

If you try to pack more and more air bubbles into a space, at some point there's no room between them and they therefore are pushed together.

And that happens at about 70% air.

So, if you have less than 70% air in your milk, it's just a kugelschaum and it just comes to the top and just pops.

But above 70%, these bubbles are starting to push against each other.

You then get the polyhedra schaum, which is this beautiful shapes of tetrakaidecahedra.

Foam spontaneously forms this beautiful shape.

That's when you get the structure which allows you to do a latte art.

James Harper

So essentially, once you've been trained enough air into the milk and broken those bubbles into smaller and smaller pieces by swirling them together, you have now very small bubbles.

And if you were to zoom in to the foam and see those bubbles, they would form the shape of like a really fancy ruby on the top of a crown.

And actually, Professor Stephen Abbott has a really cool diagram of this on his website, which I've linked in the show notes.

So that's basically how you create microfoam.

However, microfoam doesn't just form with whatever ingredient you stick a steam wand into.

There needs to be a special something for foam to form.

Let me prove my point.

I asked Toby Whedon of Oatly to do something rather embarrassing for me.

So we're in Oatly's open plan office in Malmö, southern Sweden.

And you know, his colleagues are nearby having quiet conversations.

And I asked Toby to make a scene.

Can you steam me a picture of H2O?

Toby Weedon

I can give it a good go.

James Harper

I want you to make me the best latte possible, the best microfoam with just plain water from the tap.

Toby Weedon

Yeah, I think we might need to pre-warn everyone.

Why is that?

This is going to sound atrocious.

Let's do it.

James Harper

And so as Toby steams a jug of plain water, his colleagues start looking over their shoulders.

Toby Weedon

Some of my colleagues are giving me very confused looks because normally I'm quite good at this.

Yeah, can you see how pink I've gone?

Really red.

James Harper

Oh my god, what a racket.

And then an extremely red-faced Toby tried to pour me some latte out with this steamed water.

Perfectly smooth.

Toby, there's no bubbles there.

And the best he could do was just give me a glass of somewhat hot water.

Toby Weedon

Not only did it not froth, it didn't hold any sense of air or anything.

It just became hot water.

James Harper

And bubbles were created.

Yes.

Toby Weedon

But they formed and then blew away immediately.

Yeah, absolutely.

There was nothing trapping that air within the water.

So I've got a clean jug.

But then Toby added a magic ingredient.

A pea-sized amount of...

Yes.

A tiny drop of washing up liquid.

So doing the same thing again.

And then steamed it again.

James Harper

This time, I saw bubbles forming and staying in place and getting smaller and smaller.

And it was quiet.

And there we go, that's at the right temperature.

Toby then picked up this pitcher of beautifully micro-foamed soapy water, poured some latte art into a transparent glass, and then held it up so we could see through the side of the glass.

Toby Weedon

It's like a cascading effect, which is what you'd see with a latte anyway.

It's kind of like when you pour a Guinness as well.

The effect of all of the micro-foam rising to the top.

It looks quite nice.

Quite palatable.

I was about to drink it actually, until I remembered what it was.

James Harper

So what is it about washing up liquid that transforms ordinary water into gorgeous foam?

Surfactants.

Also known as surface active agents.

Prof. Steven Abbott

So these are small molecules and you cannot see them.

James Harper

But there are a lot of them in your latte.

Prof. Steven Abbott

Trillions doesn't even begin to do it.

It's trillions of trillions of trillions.

James Harper

And a surfactant is basically just a tiny microscopic compound with one particular property.

Prof. Steven Abbott

So they have a tail which does not like water.

So the tail will come to the air surface and they have a head which likes water.

So the head stays in the water.

So every chance they have to go to a not water surface, i.e. the air, they seize that.

Let me help you visualize this.

James Harper

Imagine you're steaming a pitcher of milk.

As air bubbles are created, surfactants whiz their way over into those air bubbles.

And to show you exactly how a surfactant works, we're going to get a bit...

raunchy.

So basically, surfactants, as they're depicted in science diagrams, listen, they look like sperm.

Now, their heads like water and their tails like air.

And so these sperm-like looking surfactants dive their heads into liquid and their tails are flapping around in the air and that, when it's around and inside a bubble, it's what keeps it from popping.

And as we continue to steam the milk and the bubbles get smaller and they push together more and more and more, the surfactants keep these air bubbles stable.

So that's what surfactants do.

But what is the surfactant in milk?

Because I really hope it's not dishwashing liquid.

But you have heard of them.

Proteins.

However, it's not proteins in their normal full shape.

Prof. Steven Abbott

Nature has created these proteins with a beautiful three-dimensional structure.

What we need to make a good foam is to completely destroy that beautiful 3D structure.

So you're putting a lot of energy in with your steam wand, and some of that energy is heat energy, and heat destroys protein structures, but also it's mechanical energy that also destroys protein structures.

So you now have destroyed a protein structure, but it's still there.

If that protein has lots of water-loving things and lots of water-hating things, it can be a surfactant.

James Harper

So in cow's milk, the surfactants that keep the bubbles together is smashed up protein.

And you know, it's not surprising that milk has protein.

It comes from a mammal, a cow.

Us blood and flesh animals, we're made of muscle.

Muscle has lots of protein.

Arnold Schwarzenegger back in the day was basically just one giant lump of protein who occasionally made his way in front of a film camera.

All this to say, when you think of a little flake of oat, the key ingredient in Oatly, protein is not the first thing that jumps to mind.

So, you know, how good is it really at making microfoam?

Toby Weedon

Five double espressos.

James Harper

And this was the challenge I set for Toby back at the Oatly offices.

Toby Weedon

We have to drink all of these afterwards as well.

James Harper

I asked Toby to create microfoam and pour latte art using cow's milk as well as regular Oatly, known as Oatly Deluxe in Sweden, and Oatly Barista Edition.

And the test was which of these cappuccinos could hold the latte art the longest.

So I incorporate air at the very beginning.

And so Toby steams and pours a wonderful cappuccino with the Oatly regular.

It's a beautiful little heart there.

Toby Weedon

There we go.

I've done that once or twice.

James Harper

And then another with the Oatly Barista Edition.

There we go.

But when it comes to the cow's milk, things go a bit awry.

Here's the thing.

If you know Oatly's marketing, you know they're not friends with cow's milk.

Their slogan is, wow, no cow.

Literally, the copy bar in the middle of this open plan office, there's a sign above it that says, not milk bar.

Get it?

It's not a milk bar.

And so even the fact that we have cow's milk in the premises, that's kind of turning some heads.

Oh no, Toby, you've just put cow's milk all over the Oatly office.

But then Toby spills it.

Toby Weedon

This man over here, your colleague, is giving you the thumbs down.

It's a sign that we're not meant to be doing this in the Oatly office.

We're an absolute mess.

Okay, here goes nothing.

James Harper

All right, so that's enough embarrassing, Toby.

Let's get to the results.

It's literally breaking apart.

We can see it deteriorating.

See how quickly it's deteriorating?

The differences between how long the Oatly and the milk held their latte art patents was huge.

That's possible.

Like that latte art has still held despite being made, what, seven odd minutes ago?

So the latte art with the Oatly barista edition, the love heart was still intact 10 minutes after Toby poured it.

The Oatly barista, it's still almost at the top, I'd say.

Yeah.

Now, the cow's milk started off pretty strong, held its love heart shape for a number of minutes.

In the whole milk, already, you know, despite being made six minutes after the Oatly barista, looks worse than the Oatly barista.

But that love heart shape was breaking up much faster compared to the Oatly barista edition.

Toby Weedon

Yeah, and you can, if you look close enough, you can, for long enough, you can see bubbles joining together to become bigger popping bubbles.

James Harper

So at this point, I'm thinking to myself, the Oatly barista edition, a oat drink, is doing better than cow's milk.

However, the Oatly Deluxe has almost totally deteriorated.

The non-barista edition of Oatly, the regular Oatly, was doing terribly compared to cow's milk.

It's like a really like smudged out heart at this point.

So the worst performer was the Oatly regular edition.

The middle performer was the cow's milk.

And the best performer was the Oatly barista edition.

Wow, okay.

So something's going on here.

Something is magic about this barista edition.

Yes, there's a secret, there's a secret sauce in there.

I wanted to know, what is in Oatly barista edition that makes it so good for latte art?

Where's the surfactant coming from?

And how do you even make an oat drink in the first place that behaves like milk?

Emelie Meisner

And I think a fun fact, if you're one of those that are into fun facts, the flag they can see up there, the landmark of Oatly.

James Harper

That's a pink Oatly flag?

Emelie Meisner

Yes, it is 79 square meters big.

So it's actually bigger than my apartment.

James Harper

That's 79 square meters?

Emelie Meisner

Yep.

That looks tiny.

Yeah, it's high up in the air.

James Harper

So to understand how Oatly is made, and where the surfactants come from in their barista edition, well, I went to their factory in southern Sweden, Landskrona.

Emelie Meisner

Here's the loudness and the heat and all of it.

James Harper

Oh, it is hot.

You weren't joking.

This is really warm here.

And that voice you're hearing was my guide, Emily.

Emelie Meisner

I work as a community manager for our global team.

So basically handle all external communication towards consumers for Oatly.

James Harper

And I gotta say, the whole experience felt like I was visiting a submarine.

I mean, this is such a maze of pipes.

I mean, pipes were crisscrossing left to right, under my feet, above my head, through different rooms, on the walkways.

It sounded like we were 200 meters underwater in a metal tube.

Even the windows on the doors were the same as a submarine.

All the doors have like porthole windows.

Emelie Meisner

Yeah, they do.

James Harper

And it soon became obvious why things were so cramped.

Emelie Meisner

So yeah, up until 2019, this facility was the only facility providing Oatly globally.

James Harper

Every single carton of Oatly drank in America, Britain, Australia, you name it, was produced in this factory up until 2019.

Amazing.

Are you ready?

I'm ready.

Emelie Meisner

Let's do this.

James Harper

So let me walk you through how Oatly is made.

Emelie Meisner

Looking into here.

James Harper

First step, you pour in truckloads of oat kernels.

Emelie Meisner

You know one of those like paper shredders?

James Harper

Slice the hard oat kernels into tiny little pieces.

Emelie Meisner

If you go inside, it looks like a huge paper shredder with like knives in it.

Sofia Eldhe

Step two.

Mix the oats with hot water.

So it becomes like a oat porridge.

James Harper

And this, by the way, is Sofia.

Sofia Eldhe

I'm Sofia Eldhe and I'm the global lead of food innovation at Oatly.

James Harper

So we now have our oat porridge.

Step three.

Sofia Eldhe

Like when the oat bases travel, it goes into the enzyme tanks.

James Harper

You add in some enzymes.

Sofia Eldhe

To break down the starch to smaller carbohydrates.

And you get a sweet taste because when you break down the starch, you get the shorter carbohydrates like maltose, for example, which has a sweet taste.

And by the way, this process, you yourself do it without even realizing.

And that's the same kind of process that would happen in our bodies when we break down starch.

James Harper

Because, fun fact, we create in our bodies a ton of enzymes in our mouth, stomach, pancreas and small intestine.

Emelie Meisner

You know if you take a handful of oats and you chuck it in your mouth and you chew it, we've kind of replicated the human process of breaking down starch in oats.

Sofia Eldhe

And now, step four.

We still have the insoluble fibers in the products that make it a bit chewy.

So we separate them to get the milk-like consistency.

James Harper

So you take away the chewy bits and what you're left with is something that behaves a lot like cow's milk, but it's made of oats.

So where in all of this process do you find surfactants?

In cow's milk, it's the protein.

And when it comes to oats, they have protein as well.

So oat has protein?

Sofia Eldhe

Yes, oat is quite rich in protein compared to other cereal crops.

James Harper

But do oats have enough protein as cow's milk?

And is that enough to make good latte art foam?

We have two Swedish cow's milks.

Protein levels are the same, 3.4 grams.

In that latte art experiment I showed you earlier with Toby, I looked at the nutritional label on the side of the cartons and milk came in at 3.4 grams of protein per 100 mils.

Oatly, if we look at the...

Whereas for Oatly...

Protein is one gram.

So both versions of Oatly had less than a third the protein of cow's milk.

And yet the barista edition performed the best and the regular version, the Oatly Deluxe, performed the worst.

And this is where I realized the amount of surfactant isn't really the issue.

Professor Stephen Abbott said to make good foam, you need just a tiny amount of surfactant.

Prof. Steven Abbott

These will be just 0.1% or a very small concentration.

They do their magic.

James Harper

And at this point in my latte foam journey, I was desperate to know, what does Oatly do differently with their barista edition compared to their regular version?

And when I was speaking with Sophia Elder, Global Lead for Food Innovation at Oatly...

Is an emulsifier added as well to the process?

One of my first theories was maybe they are adding a surfactant in it, like an emulsifier, but no.

Sofia Eldhe

No, we don't need that in our technology.

So the way we use the oats and make the oat drink, it brings out that ability from the oats.

James Harper

No surfactant is added to the barista edition, but there is something special they do to the proteins.

Sofia Eldhe

What we do is that we make sure that the protein that is in the oats is available so it can help stabilize the foam.

James Harper

And unfortunately, I can't tell you exactly what they're doing.

And that's because I don't know.

Nobody does.

Well, except for the handful of food scientists who Oatly employ and have signed NDAs, non-disclosure agreements.

It's a trade secret.

So if you really want to find out yourself, become a food scientist, go work at Oatly.

But I don't want to leave you here high and dry.

Let me tell you just how weird and wonderful surfactants can really be.

To give you a clue as to the sort of things Oatly may have considered doing to make the proteins better surfactants.

And to give me these ideas, I spoke to another food researcher.

Nidhi Bansal

So I'm Nidhi Bansal.

I'm an associate professor of food science and technology at the University of Queensland.

James Harper

Could you talk about like, what can you do to a protein, right, to make it a better surfactant?

Nidhi Bansal

So depending on the type of the proteins, the protein has to go on this air interface and they have to then open up or denature, so to speak.

James Harper

So some things you could do.

You can change the shape of the surfactant.

Nidhi Bansal

And go to the air interface much faster.

James Harper

Or you could change how quickly it gets to where it needs to be to create foam.

Nidhi Bansal

Just because how the pH affects the protein properties.

James Harper

The pH of the solution also has an effect.

And there are many more things besides.

I won't bore you with the details.

But having gone on this surfactant deep dive, one thing that I thought was really impressive is how Oatly is able to create better surfactants using just oats.

Like the oat itself is capable of so much.

And Sophia also feels the same.

Sofia Eldhe

Well, oats is such an amazing crop.

It has an amazing potential.

So there is so much more we can do with oats.

James Harper

And she said there were plans afoot to find even more ways to use the humble oat.

So we've just explored how you create foam and how to make a foam last for longer.

And back at the Oatly offices, after I had interviewed Toby for a little while.

Let's see how the foam has held up an hour and 10 minutes after we began the experiment.

We went back to see the results of our latte art experiment.

Whoa, interesting.

Wow.

Okay, so beyond the fact we're looking at an absolute mess, a catastrophe of latte art.

Um, what's happened?

Toby Weedon

All of the foam has essentially disintegrated on all of the drinks, leaving a few very large bubbles that will continue to pop and combine until we end up with one homogenous liquid.

Unfortunately, the cold hard truth of the world is that every bubble has to burst.

James Harper

But why?

Why is that the case?

Let me introduce you to two of our prime suspects.

First suspect, gravity.

Prof. Thom Huppertz

Because of gravity, fluid will start flowing down and that's really the fluid that is draining out of the foam.

James Harper

And this is Professor Thom Huppertz.

Prof. Thom Huppertz

Professor of dairy science at Wageningen University in the Netherlands.

James Harper

Interesting.

So as liquid drains out, what happens to the foam itself?

Prof. Thom Huppertz

When the liquid between the air bubbles moves out, the air bubbles start coming closer and closer together, start touching eventually.

And they start coalescing.

Do we get coarsening of the foam?

And eventually that will start leading to collapse of the foam as well.

James Harper

So that's drainage.

Gravity pulls liquid between the bubbles down and the bubbles start coming in contact with each other, which is where our second suspect enters the scene.

Prof. Steven Abbott

It's called Ostwald ripening.

So Ostwald ripening means that if you start with a variety of bubble sizes, the bigger ones will grow at the expense of the smaller ones.

And when they're big, they just become soft and weak and fall apart and drainage gets faster and all those things.

James Harper

Small bubbles become part of larger bubbles and eventually when a bubble gets just too big...

So that's how gravity and Ostwald ripening destroys our beautiful latte art patterns.

James Harper

But many a foam and food scientist may say that, hold on, there's also a third suspect.

Fat.

And this is where, frankly, scientists and baristas don't see eye to eye.

Representing Team Barista, Toby Whedon steps into the ring.

So Toby, what's been your experience steaming low-fat, you know, 1.5 fat milk?

Is it easier or harder than full-fat?

Toby Weedon

I find it more challenging with the lower-fat content.

I'm not really sure quite why that is.

I've always just found it more challenging and I think the fat really does contribute to the foam.

James Harper

Ask any barista and they will tell you it is harder to make good latte art using semi-skimmed low-fat milk compared to full-fat.

Full-fat is much easier.

But according to many of the scientists I spoke to, it should be the other way around.

For example, I had a wonderful conversation with this researcher.

Dr. Rituja Upadhyay

My name is Dr. Rituja Upadhyay.

So basically you can call me as a product development and sensory scientist.

James Harper

Rituja is in the world of food engineering.

Like, she understands fats and foams.

And she said there are many reasons why fats are bad for foams.

For one.

Dr. Rituja Upadhyay

Now, fat globules, as I said, they are very, very heavy in nature.

James Harper

Fat globules are relatively heavy.

Not exactly what you want hanging around in a delicate foam structure.

Dr. Rituja Upadhyay

They cannot hold that much weight of those globular fats and therefore the possibility of the collapse of the foam is much, much higher compared to the skimmed milk fat.

James Harper

But it doesn't stop there either.

Because the scientific research suggests that when you steam a pitcher of cow's milk, you can shred up the fat molecules.

And when these pieces of shredded up milk fat make their way into foam, they can quickly go to the interface of the gas and the liquid when the foam is formed.

Prof. Nidhi Bansal

They can displace the proteins and they can interfere with proteins in forming the foam.

James Harper

This is Professor Nidhi Bansal from earlier.

And her argument is that the fats are giving the surfactants a run for their money.

Prof. Nidhi Bansal

In a sense, they are basically competing with proteins.

So the proteins can't perform their function.

They can't actually form this film that keep the bubbles stable.

James Harper

And these are just two of many arguments I came across as to why skimmed milk, low-fat milk should be better at creating foams than full-fat whole milk.

But there was also one scientist who was just like, I don't know.

I've been looking into it for a bit over the years and I still can't explain it.

And so calling all milk scientists around the world, hell calling all scientists period.

Please answer this mystery for me and all the baristas out there.

Why is it that we coffee lovers find it easier making latte art with whole milk?

And here's something else I found rather interesting.

Imagine you are Oatly and you are developing a version of Oatly good for latte foam, the barista edition.

Too fat or not too fat?

Or how much fat did they use?

What kind of fat did they use?

Now here's a fun fact.

Oats have fat.

Sofia Eldhe

There is fat in oats.

If we would not add anything, we would have about half a percent.

James Harper

Half a percent.

Who would have thought?

Much less, of course, than the three or four percent you might find in full-fat cow's milk.

But in any case, Sofia and her team had to decide, do we increase the level of fat?

And if so, to what?

Which team did they support?

Academic scientists saying, hey, that's a bad for foam or baristas were saying, hey, latte art is easier with full-fat milk.

And they chose team barista.

As they developed Oatly barista edition, they collaborated with local specialty coffee baristas in Malmö and they settled on three percent fat.

Very similar to full-fat cow's milk.

Sofia Eldhe

Yeah, we also tried to have a lower content, but we found that three percent was perfect.

So what happened with the lower content?

It wasn't as rich and creamy in taste.

James Harper

And did you go beyond three percent?

Did you think, hey, let's jacket the five percent, 10 percent?

Like, what did that taste like?

Sofia Eldhe

If you go too high, it's more like adding cream to your coffee.

So I think it's a different taste experience.

We didn't go that high because we also wanted it to be nutritionally relevant.

We aim at people having lots of lattes.

And of course, if you have too much fat, you eat too much fat.

It's not healthy to have too much fat.

James Harper

So in the end, they chose three percent because it tasted better and it wasn't ruining the quality of the latte art.

And the fat they use is canola oil.

It's got a creamy texture, produced natively in Northern Europe, and it has a neutral taste.

So the big question, after everything we've covered, what can you do to make better latte art at home?

Well, really the one big thing you should focus on is practice creating small bubbles.

Steven Abbott

You know that a beautiful latte foam is very small bubbled.

James Harper

Don't worry too much about pouring patterns.

Focus on creating microfoam first.

And there are many, many reasons.

For one, you can pour an intricate pattern better when the bubbles are smaller.

I cannot tell you the number of times I've been scrolling through coffee Reddit and people showed their latte art and it's just a big fat squodge because the bubbles are just too big.

My advice to them is always make better microfoam first.

And now here are even more reasons why smaller bubbles are better.

Steven Abbott

Those small bubbles give it the stability, the stiffness of a foam.

Scientifically, it's called the yield stress.

Depends on a number of things, but mostly it's on the bubble size.

So if you have small bubbles, you have a stable foam.

James Harper

Smaller bubbles keep your beautiful latte art together for longer because they slow down the process of drainage.

You know, where gravity pulls the liquid away from in between the bubbles.

Steven Abbott

The best thing for slowing down foam drainage is to make small bubbles.

James Harper

And the final reason is what I mentioned at the top of the episode.

Microfoam just feels more luxurious.

And this is why.

Dr. Rituja Upadhyay

What exactly is happening inside the mouth is the bubbles, they come together to coalesce.

James Harper

As in when you take a sip of a microfoam latte on the surface of your tongue, small little bubbles are coming together to form larger bubbles.

Dr. Rituja Upadhyay

So coalescing gives you a creaminess feeling inside your mouth.

James Harper

So small bubbles are the way, but creating them is tricky and it's going to take a lot of practice.

I'll put a link in the show notes to a YouTube video to help you while you practice.

But if you are a bit more pro geeky, maybe you fantasize about winning a latte art smackdown.

Here's something really cool that Professor Stephen Abbott showed me.

You can actually, with your phone, measure the size of latte art bubbles.

Steven Abbott

And there's a wonderful trick where you just have a prism and you put in contact with the foam, you have your smartphone and an LED light source and you take a picture.

And there's an app on my site where you can take that picture and measure the bubble size.

James Harper

I've linked this in the show notes, but you're going to need a glass prism.

Bit tricky to come by, but nothing will stop a true coffee geek.

And now here's my fantasy.

What if we as an industry began to experiment more, to find techniques which got us smaller and smaller bubbles.

And we can measure this with, for example, the app that Stephen Abbott developed.

And as we compete to get smaller and smaller bubbles, our foams last longer and longer, the latte art better and better, the drinking experience ever more sublime.

And over time, we start convincing more people to spend a bit more on their lattes.

And that makes this entire industry more financially sustainable.

So thank you for listening to the penultimate episode of this series.

Very sad, very sad.

Only one more to go.

Now, if you enjoyed this, please tell a friend.

Better yet, tell two friends.

You know, this show relies on word of mouth.

I don't have an algorithm promoting me.

I don't have a big marketing budget.

It's just me making this show.

And I really believe that if anybody pours their heart and passion into something, the world will appreciate it and share it.

So yeah, if you enjoyed it, tell some friends.

And if you're on Instagram, an idea, take a screenshot of your podcast player and post that as a story.

Tag me at filterstoriespodcast and I'll know it's you and I can thank you personally.

And I promise I will repost it too.

Now, this episode is a product of many, many people graciously offering me their time and expertise.

Stephen Abbott, by the way, he has a really cool website on kind of pop chemistry.

A bit on the nerdy side, but hey, if you're a science geek, check it out.

Rituja Upadhyay, Nidhi Bansal, Tom Huppertz.

And also, importantly, the really wonderful team at Oatly, who went out of their way big time to support the story that I wanted to tell.

And in particular, a big shout out to Sophia Elder, Truby Whedon, Emily, Lucy Hopkins Parkinson, Leonire Nudstrom, and many, many more.

You know who you are.

Thank you.

So what's coming up in the last episode?

I'll tell you what, you can listen to it right now because it's already out on the Science of Coffee channel.

Link in the show notes.

But it will be a two-parter, one half looking at sonic seasoning, and a second exploring the science and R&D landscape in coffee more generally.

And I'll take you into the grinder manufacturer Fironzato, into their factory, which, by the way, sounds a lot like Oatly's.

However, the difference?

Many more robots.

And if you haven't heard the other episodes in the series, the first is about good water for coffee.

And there, I explore the concept of buffering capacity, which massively impacts the acidity of a coffee.

And I show you how BWT, a water filtration manufacturer, they create filtration kits to reduce the water's buffering capacity.

So, you know, a coffee is more acidic.

But Oatly, on the other hand, have the opposite problem.

Coffees are so acidic they can sometimes curdle Oatly, which is why they added an acidity regulator in the barista edition of Oatly.

Basically, increase the buffering capacity, reduce the acidity.

And one type of coffee that might be very acidic is a coffee from Kenya.

And by the way, I visited Kenya with the green bean supplier Triboca, and I saw how they work with farmers to create high-quality acidic coffees.

And that journey and a wider exploration of the role of coffee genetics in tackling climate change, I explore all of that in the third episode.

The second episode is on coffee extraction.

And honestly, once you've gone through the process of making a really good filter coffee, many people in specialty will tell you, please don't add any milk.

And for example, once you know how much work went into Marco Beverage Systems SP9 Brewer, where they try to control so many filter coffee variables, you'll know why specialty coffee people say, please keep your filter coffees black.

And finally, the episode before this one explores the development of espresso machines, and how a lot of this culminates into the fully automatic machines created by Eversys.

And I don't really go into this, but they have a really cool way of entraining air into the milk.

Because the problem is, it's a really dense box, and they can't pull in ambient air.

So their solution is to basically supply air like you would to an astronaut.

Now, The Science of Coffee was produced by me, James Alpern.

I also write and play the piano music.

I want to give a big thanks to Peter Giuliano and Britta Fulmer for their editorial guidance.

And thank you again for listening.

Good luck getting your latte bubbles smaller, and I'll speak to you next time.