How grinders work deep inside

So on a cloudy day in late August, I woke up in an Airbnb on one of the hills surrounding Zurich, Switzerland. I finished breakfast, unfurled my Brompton bicycle, and then whizzed my way down to the sponsor of this episode, Mahlkönig, a world leading manufacturer of coffee grinders. I park up my bike outside a tall glass building, walk in and meet the man in charge of the research and development department.

My name is Arnaldo Rodrigues, I'm the group head innovation and technology for the HEMRO Group.

Arnaldo walks me over to the lift and presses minus one.

Minus one it is. This is our secret R&D area.

Literally in the basement.

It is in the basement, yes.

The doors open to their R&D lab. I find this very quirky blend of old school machinery. The Colchester Master 2500.

This machine, which is the size of a sofa, cuts grooves into metal.

And they're still working after so many years as well.

But then I also see space age tech. It's like a moon vehicle or something.

It does look like that.

A moon base, miniature model.

You know, it's funny you say that because we are in an industry that is dealing with microns.

And also, Mahlkönig this year have turned a hundred years old.

You can see up there we've got some of our legacy grinders as well.

You can say that again, that is a legacy. Which is why up on the shelves, I could see some super retro coffee grinders.

It's reminiscent to kind of a...

Gas station, like 1930s gas station pump.

Yeah, it looks like that, right?

My Lord. So I'm here in the R&D lab because the Mahlkönig team wanted to show me an experiment. You have set something up here.

What's going on?

Yeah, so we will compare two different set of burrs.

The Mahlkönig team are going to make two espressors for me. The only difference are the burrs, which are the metal disks deep inside a grinder that actually do the coffee grinding. Now, to me, they both look like perfectly normal coffee burrs.

They look identical almost.

They look almost identical.

They grind up the same coffee using these two different burrs. And to me, the powders look and feel identical. What's crazy is that just look at these powders.

They look the same to me. It's the same powder. How could it possibly be different?

You can't feel a difference.

And then they pull the few double shots of espresso.

Okay, coffee number one.

Here we go.

The first pair of shots, a little bit on the longer side, but otherwise pretty standard. So we got 91 ml in 31 seconds. The espresso didn't run particularly fast, finished in 31 seconds.

It's your classic well-extracted espresso. Sweetness, body, bit of acidity, some nice chocolate notes coming through. Okay, so now we have the burr number two.

But then we made the second coffee. Oh, wow, that's much faster. Wowzer, that's gushing through.

What? It's over already?

What, are you kidding me? The hell?

This second coffee finished in seven seconds. And it tastes watery, weak, very sour.

So, here we have two sets of burrs, which to me look pretty much identical. And they create a coffee powder that feels the same in my hand. They have the same average particle size.

And yet one of them gushed through, and the other was a perfectly normal espresso.

You can see this minute difference, so an apparent difference in the particle size distribution has a huge impact.

That's unbelievable.

In this episode, I'm gonna take you deep into the science of grinding. We're gonna spend time in Mahlkönig's R&D lab in the bowels of this company to show you why tiny differences can massively change the flavor of our coffee. I'm gonna show you how grinder burrs are designed, manufactured, and all of this will help you understand what kind of a grinder you need, and why it is that spending more on a coffee grinder may not necessarily get you a better coffee.

I'm James Harper, and this is The Science of Coffee, a spin-off series for my coffee documentary podcast, Filter Stories, and a journey into coffee's hidden microscopic secrets.

So to start us off, I want to give you a better idea of what a Grindr burr is by showing you how they're manufactured. Testing, testing, testing, testing, testing.

It's working fine. So on a cold November day, I hopped on a train from Berlin to Hamburg, and I went to visit Mahlkönig's gargantuan factory, where they make one million burrs every year. Oh, wow, this is a, oh my god, it's just got 10 times bigger.

So yeah, so that was assembly.

There were dozens and dozens and dozens of machines as big as SUVs, each costing what, half a million, a million euros each? One long rod.

And then they're cut in pieces.

And they in turn would get these very, very long steel tubes, slice them into disks, like ice hockey pucks. Here we have the robots.

Robots.

And then using robots and precise machinery, they cut teeth into these disks.

Wow, look at that.

You know, and honestly, looking at some of these machines, I felt like I was in the movie set of Alien. Like, you know, the alien opens its mouth and it drips out.

And so once these metal disks have these teeth cut into them, they're polished down with one of the finest, siltiest sands I've ever felt in my life. It's a kind of sand that you... It's going to take me like a good 20 minutes to get this off my hand, you know.

So fine. And at the end of this whole long process, what we have sitting inside a grinder are two birds. All right.

Now, let's zoom into their teeth.

Now the So back in Zurich, Chris Meier, Mahlkönig's systems development manager, put in front of me some burs.

So these two look quite identical, and these two are slightly different.

Think of them like flat metal donuts. They're these metal disks, maybe a centimeter wide, and like a donut, they have a hole in the middle. And on one side of each disk are all these different teeth, like grooves, lines in the metal.

Fantastic. When they were there in front of me, I tried to describe what those lines look like. I'm just going to try to describe these.

So essentially on the left. And totally failed.

Good luck in describing these disks.

No, I think the easiest way to describe what's going on here is actually just to turn on a grinder and show you the path a bean takes in between these two disks. So one of those flat burrs is attached firmly in place, doesn't move at all, but the other one is attached to a motor. And that motor spins the disk incredibly fast.

So usually we talk about 1400 rpm when grinding.

Wow, 1400 revolutions a minute.

Yes.

Now, remember how these disks are like donuts? The bean falls into that donut hole and it goes in between grinding teeth. Working outwards from the center are three rings of teeth.

And then we call them the main teeth, middle teeth and the fine teeth.

And they function the same way as the teeth in your mouth. So you have your front teeth at the beginning, they do the big bites.

So we need them to what we call the main teeth, the biggest one for crushing the bean into kind of small portions.

Then you have the teeth next door, which do small bites.

So they do kind of a middle crushing between that still relatively big particles of the bean.

And then the molars at the back that do the very fine chewing.

So this is the fine teeth, which, for example, at these discs, I think is 0.15 millimeters deep.

Now, of course, the teeth on these burrars don't look like human teeth. What they actually are, are these different sized grooves in the metal, like diagonal slants that are quite sharp to the touch. In the center, there are these big deep slants and the outermost ring are these very fine tiny diagonal cuts.

Okay, now, let's rewind to the top of the episode. You have set something up here. What's going on?

So we will compare two different set of burrs.

I showed you an experiment where two sets of burrs, which looked identical to me, made a powder that looked identical, they both had the same average particle size. And yet, one set of burrs produced a nice, full-bodied, sweet, creamy espresso. We got 91 ml in 31 seconds.

But the second set of burrs… Oh wow, that's much faster. Produced this weak, sour, horrible, watery espresso.

It's over already? To hell! The difference between those two coffees…

This has to do with how much fines you have in the burrs.

Was the amount of fines the burrs produced. Okay, so what is a fine?

I like this analogy a lot.

Luca Lange, Mahlkönig's former community manager, He used the analogy of like when you break a cookie into smaller pieces.

If you take a cookie and you break it in half, you have on your table some crumbs. The more you break the cookie, the more crumbs you will have on your table from breaking it. The same with coffee beans, right?

It's brittle. So once you break it, you will have some fines.

So fines are like crumbs, tiny, tiny coffee crumbs. And to us, when we're grinding coffee, you know, you often cannot see these particles. They are so small.

Wow. That's four point, that's five microns across, four point eight microns. That's tiny.

You wouldn't even see that fleck of coffee. It's like the tiniest fleck. But Mahlkönig has a particle analyzer and they show me some pictures of these fines.

Oh, wow. So you can go to every single unique little particle, look at its specific dimensions. That's crazy.

They were so small that on this machine, you could literally count the pixels. At this point, it's just like literally five, just like 10 pixels, like no more, you know. And when I imagine like a tiny, tiny coffee particle, I picture this perfectly circular little ball.

But that is absolutely not what they look like. It's extraordinary, like the diversity of shapes here. Just I felt like I was lying on my back in a field, cloud watching.

Honestly, here's one that looks like Elvis Presley's hairdo. There's another one that looks like Africa, the continent of Africa. Yes.

Scandinavia here.

That's Scandinavia.

Scandinavia.

I see a pistol. I see a bird flying midair.

There's a manatee as well. It's everything. All shapes are beautiful.

So these tiny, tiny flecks of coffee that are shaped a bit like Africa, manatees, they are very important when making espresso because they create resistance.

Fines do play a certain role, as you know, because…

To explain this, Arnaldo uses an analogy.

So imagine large balls and then you've got football balls and then you've got tennis balls.

Imagine a big basket full of soccer balls and then you pour in this bucket of water on top. That water will rush through in between the soccer balls and drain out extremely fast.

But what if you threw in a bunch of tennis balls as well?

Then if you throw tennis balls within the population of football balls, then they fall into the spaces that is available to them.

If you were to dump another bucket of water on top now, the tennis balls, they're going to block the path of the water. They create resistance. The water flows out slower.

And the tennis balls are basically the fines, essentially. And if you have these fine balls falling into these spaces, then what they do is add more resistance to flow to the amount of water that you are pushing through the puck. And this makes a big difference in terms of what you end up getting as extraction time.

So this is what's happening inside an espresso puck. These tiny fines, they sit in the gaps between these big chunks of ground up coffee. And when the espresso machine pushes nine bars of water through, they slow down the water.

This increases the contact time between the water and the coffee, thereby giving the water more time to pull out flavours from the coffee, which can make your espresso taste stronger. But also the coffee is more evenly extracted. If there aren't enough fines, the water finds this channel, this path of least resistance, and just gushes right through.

But there's a lot of coffee on the edges of that coffee bed that isn't getting much water at all. With fines, the water saturates everything much more evenly. You get a more even extraction.

So in that experiment, one coffee came out in 7 seconds, and the other in 30 seconds. And the difference between those two espressos was the proportion of coffee fines.

Because of this fine share, it will have more resistance in the puck.

But what I found really crazy was that difference. It was tiny, tiny.

So this is the peak, and here you can see that it is around 2.5 to 300 in this area.

So, Luca showed me two graphs. These were particle distribution curves. Basically, when you grind coffee, the coffee beans are broken up into millions of particles.

You are safely looking at one coffee bean being 30,000 to 50,000 particles, average.

Hold the phone, hold the phone. One coffee bean is turned into 30,000 to 50,000 particles.

Yeah.

And by the way, that's for filter. If you are grinding for espresso, one bean could be smashed into hundreds of thousands of little particles. And all those different particles have different sizes.

One is large, one is small, one is even smaller. And what you can do is put it on a graph and so you can see how much space is taken up by coffee grinds of different sizes. Now the particle distribution graphs for the coffee that ran fast and the one that ran normally, both curves, they kind of look like the McDonald's logo.

You know, the golden arches. I avoid McDonald's as much as possible, but I couldn't find a better way to describe this in audio. So you have the McDonald's M, which is basically two arches.

Now imagine if that first arch was a lot smaller, just a quarter of the height. And the second arch that makes up the M is normal sized. So it's like a little arch and then a big arch.

Both these grind distribution curves look like that. But to show you the difference between the two, let's have some fun and do it musically. So the higher the note, the smaller the particle, the lower the note, the bigger the particle.

The softer the note, those particles take up a little bit of volume. The louder the note, those particles take up a lot of space, a lot of volume. Okay, so here is the grind distribution curve in music for the coffee that ran through really, really fast in seven seconds.

So could you hear those two arches, those two peaks? There was a small peak, you know, in and around 35 microns, and a huge peak around 250, 300 microns.

So basically, in this coffee powder, quite a bit of space is taken up by the coffee vines, but most of the space is taken up by the bigger pieces of coffee at around 250, 300 microns. So here it is one more time.

And now here's the espresso that ran through normally.

The point is, they're both extremely similar, but there is an important, subtle difference early on in that first peak amongst the coffee finds. Here's the one that ran really fast.

And here's the one that ran normally.

Notice, the one that ran normally is slightly louder, maybe 20% louder. And you know, when we see that difference on a graph, like it seems small, but that is actually misleading. So to help conceptualize this, let's go back to that analogy of the basket of soccer balls with tennis balls filling up all the cracks.

Now imagine, we take out one soccer ball and replace that volume we just took out with tennis balls, which is like what, eight tennis balls or so? Those tennis balls, they now sink deep into the basket and they find eight different gaps to plug up. That can be enough to block the path of the water so much that an espresso shot slows right down from seven seconds to 30 seconds.

Put another way, that subtle difference we heard in the number of finds actually equates to millions and millions more little tiny particles, which means the espresso that ran normally had millions more tiny little gaps being filled up by all these tiny particles.

So zooming out, Mahlkönig developed these two different burrs that had slightly different types of teeth. The number and size of the coffee grounds was very, very similar, but for very complicated mechanical reasons. When those two burrs came together to grind the coffee, the ways in which those sharp teeth cut and sliced the coffee produced millions and millions more of these tiny little particles, which was enough to dramatically slow down this shot of espresso from 7 seconds to 30 seconds.

And now you might be wondering, well, what are those complicated mechanical reasons that produce more or fewer finds? So, here are some of the mechanical complexities deep inside these grinders.

Reason number one. Whether those burrs are sitting upright or flat makes a difference. Imagine two coins stacked up on one another.

Those are the burrs. Now, instead of having them flat on the table, what if we flip them upright? So, they can roll across the table on their side.

These are called vertically aligned burrs. Now, imagine one coin is fixed in place and the other spinning incredibly fast with a tiny gap between them. And these burrs are like donuts, so they have these holes in the middle.

And so, as one of the burrs spins fast, a shaft feeds coffee beans into the middle of that hole and then gravity pulls these beans down through the spinning disks.

In a vertical aligned grinder, you would put the beans in, and then with gravity, the beans just fall out once they achieve the grind size.

Gravity helps pull the powder out of these spinning disks a little bit faster. And so, they leave the burrs relatively quickly. But if those burrs are aligned horizontally, like two coins stacked on top of one another, gravity here isn't helping pull the beans through the burrs.

The coffee bean is only moving through because of the centrifugal force of the spinning disk, which means they stay in between these spinning disks that little bit longer. And the longer it stays in these burrs, the finer and finer the coffee is ground up, the more fines you create.

On the horizontally aligned grinder, you have the flapper that will retain the grinds. Even if centrifugal forces push them out, the flapper will retain them. So they will stay in the grinding chamber for a little bit longer.

And again, through bean-to-bean wear, they will even break down a little bit further, producing more fines.

Now, reason number two, why one grinder might produce more fines than another grinder. And that has to do with the number and depth of those final, very, very fine teeth.

So it defines the maximum exit size of the coffee grounds.

Just before a coffee particle is shut out of those burrs, the smaller the teeth are and the more teeth there are, that also tends to produce more fines. Now, reason number three, power. The faster you spin those burrs, the more fines you're going to get.

And this one was actually a little bit unintuitive to me when I first heard it, but imagine this, right? 20 grams of beans are ground up all at once super, super fast. The beans are dragged into that doughnut hole in the middle really, really fast.

But because there are so many beans at once, they get stuck in a traffic jam. Right at the edge of those burrs, the gaps for the coffee to shoot out of where the very fine teeth are, there's only so much coffee that can go through there at any one time. Arnaldo explained it to me like this.

Imagine now if we have a number of people trying to race through a door at the same time.

People are just waiting, queuing behind to get through that door. But because they're spending more time waiting to get out, the burrs keep crushing them smaller and smaller.

It's grinding coffee on coffee. And that's how you get the fines.

I could go on and on. There are so many other reasons. But for the sake of our sanity, I'm going to draw a line here.

So for a whole bunch of complicated mechanical reasons, Mahlkönig had these two burrs where one produced slightly more fines and the other produced slightly fewer fines. And I could see these differences on a graph, the grind distribution curves, and one of those grind distribution curves, the one which had slightly more fines, produced a more balanced, flavorful espresso. And this got me wondering, like, what is a good distribution curve for making a delicious coffee?

Should the grind distribution curve have, I don't know, like one big peak in the middle like this?

Or should it have two small peaks and then a bigger peak?

What sort of grinder should I have at home to make the most delicious coffee? Can I give you a grinder to grind some beans with?

Yeah, you have one here.

Let me take it out of my bag, give me a sec. And I figured, well, maybe one way to get an insight into this is to compare what is one of the most revered coffee grinders on the market, Mahlkönig's EK43, a grinder that is minimum $2,000, and compare it to my beat up $20 old Harrier grinder that I bought, I don't know, like a decade ago. My thinking was, the distribution curve from the EK43 should show me what is the best grind distribution, and the Harrier will show me what is a bad grind distribution curve.

Because look, the EK, it's 100 times more expensive.

But it's not fair comparison.

And it's probably not surprising that the Mahlkönig team were very concerned with the premise of my test, because the results were going to be very, very different.

And there will be huge differences in particle analysis.

Show it to me. Show me the differences. I want to see the differences.

We are comparing apples with pears.

But I persevered anyway. But in order to do the test, I had a bit of a technical problem. Can you grind some coffee on that?

My Harrier hand grinder, it was so old, I lost the handle.

You do not have the handle.

I lost it. Fortunately, here in the Mahlkönig R&D lab, they have a tool for everything. Can we just attach the drill onto it directly?

So we stuck a drill on top. Harrier has never seen so much action. And turn this hand grinder electrically.

What a bloody mess.

But hey, we got a crumb coffee out of it.

And then we ground up the same coffee beans with the EK 43.

Let's go, it's exciting. We're going to the particle analyzer. And then we took the grinds to one of the most futuristic looking contraptions I've ever seen in the coffee world.

So this is what the Mars space station is gonna look like. I mean, this thing looks like a rock mining station you'd find on Mars. Basically, you throw coffee in on one end, and it carried along this conveyor belt, and then drops in front of a camera.

Oh, down it goes, down it goes. That fires gazillions of photos a second. And then it's being fired into this machine, and pictures are being taken of it.

It looks at the individual coffee particles, takes a picture of them, measures their size, and then throws this information onto a graph. The computer crunches the numbers.

We only measured four million particles.

Four million particles.

We measured, but in reality, we had over 10 million particles going through.

And then we had our graphs.

So the comparison is done now. You can see. Let's have a look.

You can see here on that. The blue curve is the Hario, and the red one is the EK43 from Mahlkönig.

All right, here's what they look like. Musically, the EK had one big peak.

So most of the space was taken up with particles about 300 microns big. There were very few tiny finds and very few big boulders. The Hario, on the other hand, it was just a lot more flat.

There were quite a lot of finds, and a modest peak, around 500 microns. Basically, the EK had more one specific size of particle, whereas the Hario was more of a grab bag. It had quite a lot of everything.

What I found really curious, like the EK, the average particle size was much finer than the Hario. And oftentimes the way grinders work is when you grind smaller, you also increase the number of finds. But despite the EK grinding much finer on average than the Hario, it had many fewer finds than the Hario.

You can see the grind of the EK43 is finer if you compare the two X50 values, even though the finds are less, even though the Hario is grinded a little bit coarser.

So this is all nice and geeky, but what does it mean in terms of flavor? Well, for me, I mostly drink filter coffee. So which of these two grind distribution curves would result in a better filter coffee for me?

So let's look at the EK43, where there was just like this one big peak and a relatively small amount of finds. Now broadly speaking, the consensus in the specialty coffee community is that the coffee will taste more acidic, more clear, but it's going to like heaviness in the mouth.

With a more uniform and homogeneous coffee ground, you will actually get more clarity. Technically you have a less of a body with a coffee, but you will have more pronounced acidity and more pronounced aroma.

So those are the flavors you'd expect to get from the EK grinds.

Now on the other hand, with the Hario hand grinder, with a less homogeneous coffee ground, you will get a higher body because it tends to be more muddy.

The flavor notes will be less clear and distinct, but because there are so many more finds, the coffee is going to feel heavier in the mouth. And it's at this point where I was like, okay, look, if I'm a consumer and I have a hand grinder at home and I'm getting a similar grind distribution curve like this Hario, you know, I'm getting quite a lot of finds, it tastes a little bit muddy. So the flavors of my filter coffee won't be so clear.

This is a bad curve, right? Like if I get a curve like this from my hand grinder, this is a bad curve, but that's not what the Mahlkönig team said. So if I'm a consumer and I get this out of my hand grinder, is that okay?

Yeah, why not? If you can make a delicious coffee of it and you're happy with the end result, that's totally fine.

And their answer was, you like whatever you like. There's no right or wrong here in terms of brewing filter coffee. And it's here I realized, ah, you know, these graphs, they're just graphs.

These graphs, they don't mean anything in and of themselves. There's no such thing as a right graph. I mean, they help you understand how you get to a flavor profile.

But that flavor profile is whatever you like to drink. And of course, you and me, we like to drink different things. And also there are so many ways we can prepare our coffees.

And you know, different grind distribution curves will have different results depending how you brew your coffee. So for example, you know, that Hario hand grinder, I could make an AeroPress with it and I think it tastes great, but my dad may not be a fan of it. But with those exact same grinds, my dad, he could make a French press, which he loves to drink, but I'm not a fan of it.

So like, yeah, different grind distribution curves interact with different brew methods in different ways, which different people like for different reasons. And this is the crux of why the Mahlkönig team don't say, this is a good distribution curve and this is not.

The question really is, how is it being prepared and who's drinking it?

So, this comparison, it got me wondering. When it comes to developing grinders, the number of things you can adjust, I mean, it's almost infinite, right? Like the size of the burrs.

Are they gonna be five centimetres or eight centimetres wide? Are they gonna be aligned vertically or horizontally? How fast are you gonna spin them?

How fast do you feed the beans into the grinder? And then of course, the teeth, the geometry of the burrs themselves.

Outer and inner diameter, they have a height, they have various angles, the vertical, and then it's also the tangential offset. You could turn the teeth to make it not cutting, but crushing. For example, the fine teeth on the EK for this rebirth is what we call rolling.

So they don't cut, they mill. And you could theoretically do that with all.

And while I was there in Zurich, we came back to this question over and over again. How do you even begin to think about what kind of a grinder to make? Do you offer a grinder that allows the barista to play with every single one of those parameters?

And if not, then, well, what do you prioritize? How do you go about developing a new grinder? And what I learned is that the way they think about it is use cases and trade-offs.

Okay, let me use an example.

Imagine a very busy cafe, pulling hundreds of shots of espresso one after another. That grinder, the priority here is to get a nice curve where the average particle size is between 200 to 250 microns.

So for a well-balanced burr, you'd expect it to be somewhere around 200 to 250.

There need to be enough fines to slow the water down so the espresso takes about 25 seconds to pull.

When you should end up more or less in this magic number or this range of 25 and plus minus a few seconds.

Also, the coffee has to be ground extremely fast.

So speed is a big thing.

And so here come trade-offs. Okay, so how big can this grinder realistically be? To grind faster, you need a bigger motor, but...

And everybody wants to have their grinder as small as possible with as much power as possible.

A bigger motor, it requires more space. Some cafes have the luxury of having large wide counters, but maybe in a city with high rents, you can't afford that much countertop space. But look, even if you do have the countertop space, if you want your coffee ground faster, okay, then you need a bigger motor, but the issue is...

And the bigger the motor, the more heat then is created.

Because the faster those burrs spin, the more friction you create, and this is an issue for the flavor of coffee.

Because obviously that leads to dissipation of aromas and so on.

Oh, oh, okay, hold on, hold on. So the hotter the burrs lead to dissipation of aromas, that's what you found in your testing?

Yes, because obviously if you had heat to the ground coffee, then you will release the oils. So you want to retain as much flavor as possible.

Now, a solution to that problem is, well, get bigger burrs, wider burrs. So there's like more metal to soak up the heat. You might even want to install a fan.

But now countertop space is becoming a real issue. And of course, the price is going up and up. And so that's why a lot of the R&D at Mahlkönig, it's really about trying to optimize all these trade-offs for very specific use cases.

The burr is needing to fulfill multiple parameter environments. So we want to make sure that we can match it to a motor, to a grinding housing that is not generating heat or high heat and passing that to the ground, that you're meeting extraction time, that you're meeting taste requirements. So it's a very lengthy development process.

It's just overwhelming. It is overwhelming. That's exactly the right wording to it.

Now, if you're in the market for a coffee grinder, and especially if you are a home coffee brewer, I mean, it can get overwhelming. There are so many considerations. Size of burr, speed they spin, type of teeth, is there a fan?

I mean, the list goes on and on and on. It's overwhelming. But look, relax.

You don't need to get so stressed about all this stuff. Here's why. Mahlkönig told me about some tests they did.

They had the same burrs, but they were different sizes. You know, one that might fit into a smaller consumer machine and a larger set of burrs for a cafe. So the burrs were different sizes.

They span at different speeds. But by adjusting the grind size, they were able to get the same flavor outcome in both grinders.

So you were able to replicate across the different size of burrs, the same flavors. So this is possible.

The thing that has the biggest impact on your coffee is the grind size. So work with it as much as you can. And if you're not happy with the results, maybe consider getting some different beans.

A really important thing I realized making this episode is that spending $2,000 will not necessarily get you a better coffee at home. Professional machines cost about $2,000 and oftentimes more because that money is buying components designed for volume. Like let's take Mahlkönig's EK43 as an example.

You find this in most good cafes.

So if you have to grind large amounts, then of course the EK is the grinder to choose. So you there have a grinding speed of, I believe it's 15 to 20 grams per second.

In your kitchen, do you really need your coffee ground super fast in three seconds like a cafe does? Are you really gonna be making hundreds of shots one after another to the point where heat becomes an issue? If I were to buy a grinder today, for me, I think what the most important thing is, is a grinder that is built to last.

Like look at my old Harrier hand grinder. It was my first ever coffee grinder. I loved it, but it's mostly made of plastic.

And as the years wore on, looking down at the ground coffee powder, I was getting more and more frustrated as I saw big chunks of coffee bean that had barely been ground at all. The issue was that the plastic components were wearing away. Towards the end, the burrs themselves were wobbling a lot.

And that would impact the flavor of my coffee.

You can imagine if you have somewhere a plastic part that can slightly move, just 0.1 millimeter, and then you have a totally different result at the end.

So when it comes to getting a grinder, my advice is get something that's gonna last. I mean, for me personally, I think a lot about the environment. I try to waste as little as possible in every facet of my life.

Buy it once, buy it well. It'll last a long time.

Now, you might think we got pretty nerdy in this episode, went pretty deep into the engineering, the science of coffee grinding. But actually, in many ways, the story hasn't even began yet. There is still so much we do not know about grinding coffee.

In the final episode of the last series, the episode Sonic Seasoning, I showed you why for a lot of grinder manufacturers, the focus is often on workflow and questions like countertop space, price. But there is still a lot of science that could be explored in the world of grinding. For example, one of the most hotly debated aspects of coffee grinding are fines.

Those tiny microscopic fragments we saw that looked like manatees or the continent of Africa. Geez, in the time I've been in coffee, I have seen fines villainized. I often heard that they would quote unquote, over extract, you know, because they're so small and they would be responsible for coffee's bitterness.

But you know, these are all theories. And if you heard the episode before this one, you now know my position when it comes to theories. What we actually need are rigorous, carefully controlled studies, looking at the role of fines sensorially.

I would like to see more rigorous tests done for how fines affect extraction dynamics in espresso and for filter, because fines are also villainized in the filter coffee world. When making pour over V60s, I often hear they quote unquote clog the filter paper, which means the water drains out slower, which makes for stronger and more bitter brews. It's these sorts of questions that have recently led Mahlkönig to work with the Coffee Excellence Center at the University of Applied Sciences in Zurich.

Maybe the results of their experiments will factor into, I don't know, like what kind of material the brewers are made of. Maybe we'll find a way to get fines that are a certain shape, that allows us to get a coffee with very pronounced acidity, pronounced flavors, but also a bigger body, a more tantalizing mouthfeel.

Who knows? There's a lot to explore, and I can't wait to taste what comes out of it.

Thank So guys, this is it. This is the end. This is the final episode in this second series of The Science of Coffee.

I hope you enjoyed it. Thank you so much for giving me your time, attention. I hope everything you've learned in this series has been helpful to you as a coffee lover, professional.

But do not fear, though, I am working on another series because, you know, there's a lot of science in the world of coffee to cover. So that'll come out in, I don't know, six, seven, eight months. You know, these things take a long time to make.

But if you enjoyed this series, please help other people find this show. You know, it's really weird. I pour a silly amount of time into making these podcasts and then they go out.

You guys listen to it, but I so rarely hear like what kind of impact it's having. It's like I'm just delivering these episodes into a void, which is why every time I see you share this on social media with other people, it really makes my day. So, anyway, if you, for some bizarre reason, have began the entire series on this episode, there's a lot of other stuff you can listen to.

The first episodes explore how our sense of taste and smell work. And with Marco Beverage Systems' SP9 Brewer, which is an automatic filter brewer for cafes, I make many batches of the same coffee, lots of different people taste the same coffees, and they all tell me how different it all tastes, which then sets me off on this metaphysical journey to answer the question, when you and I drink the same coffee, are we tasting the same thing? Then the episodes after that look at the science of roasting, where so many of coffee's flavors are created.

I visit Roost, a Norwegian company developing fully automatic roasters to understand how this cutting edge technology that enables anybody to roast coffee easily will change the coffee industry in the years to come. I then hop on a flight to Honduras and attend Let's Talk Coffee, a gathering of coffee professionals and farmers organized by Sustainable Harvest, one of the world's leading importers for organic and fair trade coffees. And it's while I'm there in Honduras, I explore the science and business of organic coffee farming and ask the question, if it's so great, why don't we see more people doing it?

And then in the episodes before this one, I show you how you can brew coffee like a scientist. And I take you on the journey I went on, to learn how to think more like a scientist. And I'm grateful to BWT Water and More, they make water filtration kits for the home and the cafe, because in that journey, I also dive into the science of water.

And it's that journey that helped me realize, when it comes to coffee science, I shouldn't get too hung up on theories. What really matters, a practical result.

The Science of Coffee is produced by me, James Harper. I also write and play the piano music. Thanks again for listening, and I'll speak to you next time.