Today we're gonna talk about crema,
that beautiful red-brown foam that sits on top
of any well-made espresso.
We're gonna talk about what it is, why it exists.
Is it good, is it bad?
Should you skim it off?
Should you leave it on?
All of this and more we shall answer in today's video.
So let's start with the name,
because the name is initially kind of confusing.
Crema comes from the Italian for cream,
but this is a foam, this isn't cream.
Why did it get its name?
It goes back to 1948 to 1950.
Achille Gaggia has got this new espresso machine.
It's brewing at much, much, much higher pressures
than anyone has brewed with before
and the espresso coming out of his machine
has this weird foam on top.
And initially people are like,
"What's wrong with the scummy foam on top of your coffee?"
And he turns a negative into a positive.
He starts to advertise his machines
as having crema cafe naturally naturale.
Natural cream coffee or natural coffee cream, I don't know.
This is a wonderful stroke of branding genius in my eyes.
He names one of the great things about espresso
and further cements his reputation
or place in history as a father of espresso.
So the name sticks.
At no point, do we really ever argue it
and at some point that Italian word becomes an English word
to represent the foam on an espresso.
So why does it happen?
Why is it unique to espresso, what's going on here?
Crema begins in the roasting process.
When you roast coffee, you generate CO2.
It's a kind of by-product to some of the reactions
that go on inside the coffee bean as it goes brown.
Things like the Maillard reaction
or the Strecker degradation.
They produce CO2 as a by-product.
That CO2 is trapped inside the coffee bean
and if your coffee bean is fresh,
there'll still be lots and lots inside it
when you come to put it in your grinder
to make yourself some coffee.
So you grind your espresso nice and fine.
You tamp it down, you put it in and you brew it.
That hot water comes into your brewing chamber
and hits that coffee.
Now, one of the properties of water is
that the higher the pressure that water is under,
the more CO2 that it can dissolve.
So that's what's kind of happening here.
As the water is passing through those grounds
at nine bars of pressure,
any CO2 that's in them that is available
is getting dissolved into the water.
Essentially you're kind of force carbonating
your brewing liquid at this point
using the CO2 in the ground coffee.
The moment, however, that the coffee leaves the basket
and it goes from being in a pressurized environment
to an atmospheric environment, right,
there's no more pressure on the coffee anymore.
Well, the water has become super saturated with the CO2
and it can't keep hold of it anymore.
It can't keep it dissolved
and so it comes out of solution as a bubble.
I'll give you a brief visual explanation of this one
to hopefully make a bit more sense.
We're gonna need two things here.
This, not particularly full bottle of espresso.
This is old espresso, it's brewed a little while ago.
It's got no crema on it whatsoever, but it is espresso
and what I'm gonna do, is carbonate it.
I'm gonna sort of mimic the espresso brewing process.
From that perspective, I'm gonna force carbonation
into the liquid and it'll be done so at high pressure,
and when we get rid of that pressure,
well something interesting should happen.
So to force carbonate it,
I obviously need a tank of CO2 like this one.
So I'm gonna use this, I'm gonna just push
some air out of here, 'cause air inhibits carbonation
and then...
So it might not look like it,
but the excess CO2 is dissolved now into the coffee below,
just like when you're brewing espresso.
And so when I release the pressure...
And look, just like on any soft drink that you might expect,
a layer of foam has formed.
Now with espresso, the carbonation is kind of different.
It's not as intense as it would be in a soft drink.
You wouldn't get as bigger, coarser bubbles
coming out of solution as you would do in espresso.
The foam in espresso is much, much, much finer,
but the principle is really the same,
which begs the question, why does coffee foam?
In order to explain this,
very quickly we need to talk about why things foam
in the first place.
Generally speaking, a foam is a bunch
of air bubbles trapped in a liquid
and something in that liquid is called a surfactant,
a surface active agent.
It's something that wraps itself around a bubble of air
and it makes that bubble strong.
Now, the reason it wraps itself around a bubble of air,
more often than not,
is that part of that thing really hates water,
while the rest of it quite likes water.
So it's desperate.
It's sort of repelled by water.
It's desperate to find anything that isn't water.
A gas bubble is a wonderful thing,
because all the bits that hate water can face the gas,
all the bits that like water can face the water.
Now, in espresso there are a lot of different compounds
that are surfactants.
In fact, caffeine at a high enough concentration
will act as a surfactant,
but it isn't really playing a role here.
There's been a lot of research done on this
and broadly speaking, they think the active surfactants
in espresso are probably things like melanoidins,
a protein derived, roasting byproducts.
There are other things in coffee
that do play a role in foaming,
but they may not be the primary drivers of foaming.
And so that's how we get crema.
We've got our espresso,
you dissolve in the melanoidins,
some other compounds too,
CO2 gets dissolved in as well,
leaves the basket, CO2 can't stand solution,
appears as a bubble inside the espresso
and then gets trapped,
wrapped up in all these lovely surfactants
and made strong as a foam.
But somehow crema retains more of a mystique
than say, the head on a pint of beer,
but they're basically the same thing.
They've happened for the same reasons.
But what is it about crema that just gets people so excited?
Now firstly, it might be the color.
Crema looks stunning.
Now the color is tied to a couple of things.
It's primarily tied to the color of the liquid down below.
Now, espresso looks like
it's just one very dark brown color, but it's not.
A less extracted or a weaker espresso
will produce a less brown foam, stands to reason,
but it isn't just concentration,
because roast level also plays a role here.
The darker you roast coffee,
the darker the color of that liquid is gonna be
and therefore the darker the foam is gonna be.
In addition, the darker that you roast coffee,
the more CO2 that you produce and it isn't just roast.
Traditionally in Italy,
robusta plays role in many espresso blends.
Now leaving aside the debate
on whether we should call it robusta or Coffea canephora,
we'll come back to that another time maybe,
the presence of robusta has been kind of desirable
to many Italian roasters for a long time,
not just because it's cheap
and not just because it has low acidity and high body,
but because it gives you more crema.
In fact, studies suggest that robusta
typically has about twice the CO2 content after roasting
than Arabica, which is super interesting.
But it comes with one more twist.
Robusta typically has less oil, less lipids,
less fats in it than Arabica.
Now you might've made meringue
and at some point you might've learned
that getting a little bit of egg yolk in your egg white
is a no go for foaming,
because in that particular foam,
the fat in the egg yolk provides an alternative
to the air bubble for the proteins in the egg white,
which means you have a much, much, much less stable foam,
because there are choices in a way.
It can go for the fat, it can go for the air.
Same is true, kind of in espresso.
If you're brewing coffee with Arabica,
chances are your emulsion,
those little tiny droplets of oil
that pressure have emulsified in the liquid below,
well those oil droplets are actually working
against your crema.
The higher the lipid content of the coffee,
the less stable the foam is gonna be
and that's been backed up by quite a lot of research.
Now people will talk about crema as if the emulsified oil
in the crema is a really important part of it
and what makes it good.
Yes, there is emulsified oil in the crema,
but only because there's emulsified oil
in the espresso liquid and the liquid made the foam,
but it's working against the crema's lifespan
by being there and as a side note, you might then wonder,
if I paper filtered my espresso,
if I got rid of the oils in my espresso,
would I have longer lasting crema?
That's a good question.
We ran a little test.
We pulled two shots side by side.
One of which had been paper filtered
using an Aeropress filter at the bottom of the basket.
Both of them had nice crema.
Both of the cremas lasted as long
as you would want them to
and certainly longer than the sort of lifespan
in which you would typically
want to drink an espresso within.
So not worth the extra step from that perspective.
Now, one more little aspect that came up a few times
in the papers, and this goes back to how espresso looks is,
is tiger flecking or tiger stripes
or whatever you wanna call that flecking
that you'll often see on the top of an espresso.
This is very common when you brew with a lot
of different coffees, they're typically more of a kind
of medium to medium dark or dark roasts,
very light roasts, you won't get as much flecking on there,
because these flecks are little tiny pieces of coffee.
They're just tiny particles of ground coffee
that have made it through the basket
that are stuck in the foam.
These look beautiful.
They look really good,
both in the cup and under a microscope too, actually.
They look kind of interesting there as well.
There is speculation in the scientific community
that these tiny pieces of coffee
actually help stabilize the foam.
It's kind of an interesting idea.
Having read a bunch of papers, I'm not necessarily sure
I truly understand why that might be the case
and I'm not sure that I've seen that in the real world.
Interestingly, they did note that robusta
doesn't really produce that much
in terms of the kind of tiger striping or flecking on top,
which I just thought was an interesting little side note.
Now all of this leads us to
what I think is the most important question, which is,
is crema good, is it desirable?
Is it helpful, is it necessary?
Before I answer that,
I wanna talk about two other quick things.
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I will put a lot of links to different scientific papers up
on my particular website.
There'll be a link in the description
to that particular page.
If you wanna get deeper into the science,
there's one particular paper I would recommend strongly
as a starting point and I'll put in
a few little supplemental references
that you might find interesting too.
But let's talk about, is crema good?
And from a scientific perspective, it's interesting.
It's not as clear cut as you might think.
Now, crema is a great piece of feedback.
It says you've brewed the espresso pretty well.
It doesn't say if the coffee was good or bad,
if it was well roasted or badly roasted,
but it says you've brewed fresh coffee slow enough
to produce a good dense foam, you've done okay.
Or you can think of it another way,
if you brew a shot that doesn't have good crema,
something has definitely gone wrong.
But does it really enhance the sensory experience?
And here it's interesting,
because broadly speaking the answer is kind of, but no.
Now, years ago I got myself in trouble with the internet
for advocating skimming off the crema for an espresso.
It wasn't even my idea.
It had come from the coffee collective in Denmark
who've been doing it for americanos,
I did it with an espresso and was astounded
by the difference that it made.
Try it for yourself, brew an espresso,
get a couple of teaspoons and skim off a layer of crema,
stir and drink the shot
and you'll find a substantial reduction in the bitterness
and kind of roasty quality of that espresso.
It might also be lacking and you might argue
that it's more effort than it's worth and life is fine.
You can just stay and drink your espresso
and you can have a nice time.
And I won't argue with you there,
but this has been backed up by proper research too.
There was a paper published by Dr. Britta Folmer
and others, I think she talked about it in a Rico talk,
that sort of said that varying the amount of crema,
essentially varied the presence of the roasted note,
I think was their language,
the kind of roastiness essentially of the coffee,
more crema gave a more intense,
kind of a roasty quality to it.
Now that paper did also talk about
how the sort of perception or very top level,
flighty aromatics varied with different levels of crema.
Essentially they were more perceptible with more crema,
but did also say that broadly speaking,
from a sensory perspective,
there were not strong differences in the taste profiles
of the espresso, based on how much foam they had,
outside of this roasted note
that really varied across all of them.
For me, skimming espresso massively reduces the bitterness.
And I think in part, because all of those fine pieces
of ground coffee that are trapped in the foam,
well they get whipped out and taken away
and you don't have to taste them.
If you've ever ended up with any amount of grounds
in your mouth for whatever reason,
you know that they're not a fun time.
We enjoy, we taste with more than just our mouth
and our noses, how things look has an impact
and a great looking crema does enhance
the joy, the pleasure of espresso, even if it doesn't do it
in that kind of objective way.
I'd like to think crema plays a role
in the kind of tactile aspect,
but I'm not sure in a blindfold
if I could tell the difference
between one that had lots of crema
and one that kind of didn't.
The texture of espresso primarily comes from
the concentration of the liquid,
as well as the particular compounds that you've dissolved,
which is kind of down to the coffee
that you started with.
Now, I did wonder if you could actually cheat
and get more crema somehow.
So I did try force carbonating coffee beans.
Essentially, I put a bunch of coffee beans in a bottle,
squeezed out as much air as I could
and then aggressively carbonated them.
Didn't really seem to make any difference,
even if I held it under pressure for a little while.
So in case you're curious, I tried it for you,
not the biggest result.
Such is life.
So a quick summary,
Arabica produces less crema than robusta,
but darker roasts produce more crema than lighter roasts.
Fresher coffee will give you more crema.
The color of crema is about how dark the roast was
to start with and how strong the espresso
that you've made it and that's kind of it.
Crema is beautiful, but you don't need to chase it.
You don't need to worry about it.
Eking out a little bit more
may not necessarily give you better tasting coffee.
I'm interested to hear your thoughts though.
What didn't we discuss?
What should we have talked about that we didn't?
Did you go down a rabbit hole of chasing
as much crema as you possibly could
and then find that things maybe don't taste
as good as they could?
Let me know your thoughts down in the comments below,
but for now I'll say thank you so much for watching
and I hope you have a great day.
Lots of you have been asking about the French Press poster.
It's now available.
We worked with an incredible artist,
Ashley Elander Strandquist and she's done a beautiful job.
She even put me in here, which I kind of love,
as well as a few of our friends, I think,
which is kind of cool.
So you can check that out now, it's available.
Link down in the description below.
It's available for a limited time.
Hope you like it.