How to Predict Grind Changes for Espresso


How to Predict Grind Changes for Espresso

  • Most baristas have encountered the grind changing 'all of a sudden/on its own'.
  • Remember when we set the grind we're just affecting one variable that determines the actual particle size (distribution) - the aperture between the burrs.
  • The final grind is also affected by other variables like temperature of the beans, roast level, days off roast and others.
  • 'Phantom' grind changes (for the same beans) are mostly a result of temperature fluctuations INSIDE the grinder/hopper (i.e. the room temperature is less important).
  • These 'internal' temperature changes are a result of friction from grinding i.e. are directly related to how busy (or not) the barista/grinder is.
  • When you're busy (hotter grinder) the beans become more plastic (produce less fines, faster shots) and as a result you will grind finer to compensate.
  • When you get through the rush and the grinder cools - all of a sudden your burr setting is much too fine for the (now cooler) beans.
  • If you see your dose dropping it's a good sign the grinder is cooling - coarsen the grind preemptively.
  • If you see your dose increasing it's a good sign the grinder is heating up - tighten up the grind preemptively.

Transcript (Speaker: Adam Marley)

Hey everyone, and welcome back to another Tips & Tricks. So last Tips & Tricks, last fortnight was a little bit light and fun and easy. So this week lets geek it up a little bit. This week, we're probably also going to be doing our tip more so directed to barista's in service, as opposed to people making coffee at home. This is very much an espresso tip, and it's probably more relevant to people making coffee in service, lots of coffee during the day sort of situation. So one of the things that a professional barista may have noticed is that their grind size will change over its own volition. All of a sudden the shots are pouring differently. They're pouring faster or they're pouring slower and you don't know why. You haven't changed the grind setting on the grinder itself and yet the grind setting has changed.

So the thing to remember is that when we're changing the grind setting on a grinder, and this is in reference to a timed grinder, not a single dosing grinder. So not a EK43, more like a Mazzer Robur, or a grinder where you've got the hopper full of beans and then it's giving you a hopefully relatively consistent dose based on a timer which you've set on a machine, so that's the context that we're dealing in. So all of a sudden, you haven't changed anything on the grinder, you haven't changed the grind setting, and yet the grinds changed. What's going on there? So we have to remember that when we're changing the grind setting on one of these grinders, what we're changing is the distance between the burrs, which are doing the grinding. That aperture between the two burrs, that distance between them is deciding how fine or coarse our grind setting is.

However, that's not the only thing which is going to determine our grind size. So what's actually happening when we grind coffee, I mean there's lots of things happening, but really the thing that's relevant to this specific tip and that helps explain why grind sizes can change for their own reasons, and you don't know why. What's going on there is that it's not just the aperture which is important in determining the grind size. The other thing which is important, or there's quite a few things, but one of the other most important things is the temperature of the beans. Because what's happening when we grind is, one of the most relevant things for shot times and total extractions is the amount of fines which we've created in that grinding process. So the fines are cell wall fragments from the coffee beans and they're incredibly small.

They're not the small pieces of ground coffee that you can feel in your fingers. They're the little dusty bits that make your hands go brown by the end of the day, if you're a barista, get barista hands. So that's the fines, and the amount of fines which are produced at a certain grind size is not just going to be determined based on that grind size alone, but also on the temperature of the beans. The warmer the beans are, the less fines will be produced at the same grind setting. So what happens in services, you'll get busy and you'll start using the grinder more, that friction in the grinder creates heat. That heat will move into the beans, which is sitting on top of the burrs and get those beans hot. They become more plastic, and as a result, less brittle, because they're less brittle at the same grind setting at that same distance between the burrs, less fines will be produced.

As a result you haven't changed anything, but as you get busy, you may have noticed this, your shot times will get faster and you've effectively got a coarser grind setting without actually changing anything. And it goes the other direction as well. You go from a busy period to a quiet period and the grinder starts to cool down, all of a sudden your shots start choking, and you're like, "What's going on here, why that happens? Because the beans cool down, they became more brittle and at that same grind setting, which you probably adjusted to get it right for the busy period, that's now too fine and there's too many fines being produced because the grinder and the coffee has cooled down.

So the tip for this week is to keep an eye on your dose. Now you should be doing this anyway if you're a good barista. But using scales, weighing your doses, because what will happen is in these types of grinders where the coffee is sitting on top and you're using a timer, that timer doesn't know that the coffee's hot or cold, the timer stay the same. You haven't changed anything. The other thing that happens as the coffee gets hot or cold, is it becomes harder or easier for the grinder to grind the coffee. So as a for instance, as it gets hot and the coffee becomes "coarser" even though you haven't changed the grind setting, because there's less fines produced. It's also easier for the grinder to grind that coffee. And as a result, you're going to have a higher dose with the same amount of time set on the grinder.

So the tip is to keep an eye on your dose because what you'll notice is, it'll be like an early warning signal that maybe you need to change your grind setting there. Maybe because of the temperature change, because you're busier, or quieter, you're going to have to make a grind setting adjustment in order to keep the same consistent flavor that you were getting and the same shot times and everything else. What's going to happen is, if your dose increases drastically, or even just is gradually increasing, then it's a good sign that your grind setting is going to need to go finer because the grind is getting warmer. And as a result, you're getting less fines.

And vice versa, if all of a sudden your dose just nose dives when you've gone from a busy period to a quiet period, then you know, well you have a fairly good idea that it's because all of a sudden the grind has gotten much colder and now your grind setting is too fine for that temperature and you're going to need to coarsen it up a little bit. So that's our tip for this week. Hopefully it wasn't too geeky. Hopefully it was useful. And maybe not just for those professional baristas out there watching, but for everyone that makes coffee at home as well. We'll see you soon.