(upbeat music)

Today we're gonna dive into the science

of how a moka pot works.

And to be honest I thought this was gonna be easy.

I thought this was gonna be fun.

I thought that this little ubiquitous Italian brewer

that everyone uses, everyone can use,

it's gotta be simple, right?

Wrong, really wrong.

This thing broke me intellectually, emotionally.

It just destroyed me.

And I wanna tell you the journey that I've been through

trying to understand the moka pot.

So you might've seen that we've done an understanding

before, we did an understanding of the AeroPress.

This one is gonna be a little bit different

because with the AeroPress I could brew

as part of the whole video,

and it was kind of easy and quick.

Here, not so much.

One brew can take quite a long time.

And so going through all the brews just isn't practical.

So for the last week we've been doing a ton of research.

I'm gonna talk you through the tools that we've had

to do that research.

Firstly, let me show you the Franken-moka.

So this is a Franken-moka setup ready to go as it would be.

And you can see there's a sort of

mess of cables coming off it.

There's tubes, there's these weird gauges,

there's quite a lot going on.

So this rig, these two pots actually, were both built

by Gabor from SEP.

Very grateful to him for all the work he did.

He did an amazing job.

There's actually a video of him building these pots,

I linked to that down below if you wanna watch it too.

Now as for how the pots actually work

there's three temperature probes,

and one pressure sensor on the pot.

Two probes are here,

and they're actually running into the base of the unit,

into the water reservoir of the base.

One of them sits under water,

and we'll give you kind of your water temperature reading.

The other one kind of goes up through the funnel

to just below where the coffee sits,

and this should give us a kind of brew temperature in a way.

The other probe sits here on the side,

and that's monitoring the temperature of the upper chamber.

We'll talk about why that's important later.

Off the side here you can also see a little tube

running to a pressure gauge,

so we have a sort of manual reading of what's going on.

And then this transducer that then connects to my telephone,

so I can have a live pressure reading

to .01 of a bar second-by-second

as the whole brew happens.

Now he did one more mod which is this thing here,

this little tube.

What that's doing

is essentially taking the coffee as it brews

away from the pot so we can collect it somewhere else.

This means that with the SEP app

we can look at the flow of liquid through the bed of coffee.

We get a kind of flow rates to track.

So we get a lot of data points.

Beyond that we're tracking the amount of coffee

that we put in,

the amount of liquid in total that we get out.

We're doing extraction measurements here

with a VST refractometer.

So for every brew before we've even tasted it

we've collected a huge amount of data.

Now I'm super grateful that Gabor did two pots

because this one is set up very slightly differently.

And this is important for the first test

that we'll be doing.

I took off the flow tube here,

and instead put another temperature probe in down that thing

to try and get just above where the coffee is leaving

the sort of filter basket part of it,

and flowing up that tube

to kind of get a temperature of brewed coffee from that.

That was interesting.

A little bit tricky,

but it was another useful data point.

I have to say having had two pots has been amazing

because they're a little bit finicky to work with

I'm not gonna lie,

and being able to reset one while another is brewing

was super, super helpful.

I was able to brew with these pots

in a way that I wouldn't be able to without all of the data.

You can do really cool interesting things

that you can't do

without temperature and pressure sensors on there,

so if you want one of these you're in luck.

At Gabor's request we're gonna raffle these off.

There's a link down below.

We're gonna raise money for World Coffee Research.

If you're not familiar

they're a nonprofit focusing

on the long-term survival of specialty coffee

on the producer side.

So they're, they're not focused on roasting coffee

they're just on growing coffee.

For you if you donate $3 or more you enter a raffle

to win one of these things.

I'll ship it anywhere in the world that I can.

Link down below.

So thank you to Gabor for his work, his donations.

And if you want one of these,

and I tell you, you kinda do if you like moka pots,

then the link's in the description.

Let's get on to some actual testing.

So the way today's gonna work is I'm gonna go through

sort of experiment by experiment

to give you the data and the results from what we tested.

And the first thing that we tested

was starting temperature in the base of the moka pot.

If you put cold water in or freshly boiled water in

what's the difference?

So we ran five simple tests.

We started with the base at 20°C, 40°C, 60°C, 80°C,

and freshly boiled water.

Relatively easy to do,

but we did have a small quirk.

Because we were trying to be really consistent

I was weighing the water

before putting it into the base of the pot,

so we always used 200 grams of water every single time

to retain some consistency.

This meant that the 80°C water

would lose some temperature there,

and lose it again going into a cold pot.

So even though we heated the water to 80°C

before loading it in for example,

it wasn't at 80 degrees Celsius

when we started heating it up.

The results were I think really, really very interesting.

Now I'd been against using cold water in a moka pot

because my concern was that you would overheat the coffee

inside the brewer as everything heats up.

And that's a little bit of a concern,

but actually something else really interesting happens.

The colder the water in your boiler,

the colder the start of your brew temperature.

As water heats,

and it can be almost any temperature,

some of it is evaporating,

that happens kind of all the time.

The hotter it gets, the more evaporates.

And I know that it boils at a hundred degrees Celsius,

but you don't need to boil it to have evaporation.

That evaporation causes a pressure to build up,

and at some point you have enough pressure

to push water through coffee.

The colder your starting point the colder the temperature

at which your coffee starts brewing.

If you load this thing with cold water,

with 20 degrees Celsius water,

then your initial brew temperature,

the first water to pass through coffee

was about 60 degrees Celsius.

Yes, it went up to about 120 degrees Celsius

over the course of the brew,

but the very start,

the earliest extractions you do were much colder.

So at 20 in you've got about 60 to start with.

And actually the same at 40,

it was about 60 to start with.

At 60 it went up to about 65.

And again at 80 it was about 65,

though bear in mind that 80 was not 80 in the pot

at the start of heating.

By the time we got to freshly boiled water

then our brew temperature was around the upper eighties,

very early nineties.

That's really interesting.

And certainly a good idea I think

to start with freshly boiled water

in the base of the whole thing,

because it means you start your brew

with a sensible brew temperature.

Now one thing I did discover on the brew temperature front

is that it actually if you boil the water in the base,

and then start to brew

that water goes from 100 to 106, 107 very quickly,

and you end up with a very hot start to the brew

perhaps hotter than I would really want

from a taste perspective.

So actually having the water in the bottom section

be more like 80 to 90 which is what you'd get

if you poured from a boiled kettle into a cold base,

that seemed to be the better result from my testing.

So far, so good.

I had a technique out there,

I have a technique out there,

and it does recommend starting with hot water.

So at this point I felt quite good.

I felt validated.

I thought this is going quite well.

I'm hopefully gonna prove

that my recommendations were right,

maybe learn a thing or two.

Very quickly it started to go sideways.

Grind size was our next round,

and a pretty simple set of experiments,

everything run the same way.

And we went with a Niche grinder

on what would be equivalent of like a 60 setting.

I know it only goes to 50 on the numbers.

A 50, a 40 and a 30.

What I expected to see is as we went finer,

and finer, and finer,

and got very close to an espresso grind

I expected to see a drop in extraction

as channeling starts to happen.

That did not happen.

The finer we went the higher our extractions went,

but then there was a twist.

We saw something else change quite dramatically,

and that was ultimately the brew temperature changed.

Now if you think about it this makes sense.

If you're building pressure

you need to build pressure against something.

Water can only exceed 100 degrees Celsius

if it's in a pressurized environment.

So when you make a moka pot

there has to be some resistance there,

some pressure to sort of resist against

to allow it to reach very, very high temperatures.

The finer you ground the coffee,

the hotter the brew was able to get.

Oh, and the quicker that it heated up as well.

So that was kind of interesting,

and a little bit unexpected.

The very hot brews didn't taste very good,

but they were definitely much, much more extracted

than the coarser ground brews.

Now a quick note on brew temperatures

while we're talking about this kind of stuff.

If you're starting with freshly boiled water,

and you're really building any pressure at all

the interesting thing

is that you're definitely brewing with water

above a hundred degrees Celsius.

The interesting thing about it

is that it doesn't necessarily taste bad but