Tamping for espresso is riddled with an incredible amount of folk-knowledge. When I was taught espresso in 2008, I was told to practice tamping on bathroom scales (I admit I don’t remember what the prescribed weight was). Today I’d like to shed some light on tamping pressure and how easy it is to get it right.
tl:dr – Tamping pressure matters. If you press until the tamper stops moving down, and keep it level, you’re golden
Tamping is pretty simple. You’re compressing the coffee grinds to promote even extraction in an ergonomic and consistent way.
Let’s break that down a little further:
Compressing the Grinds
If there’s air between the grinds, water will treat it as a shortcut and speed through. If there’s no (or minimal) air, the grinds will slow the water down.
Unfortunately, coffee grinds aren’t always uniformly dense, and ‘somewhere between fluffy and compact’ isn’t very precise. So we need to compress them together, eliminating that void space. This way, the grind size is the deciding factor for flow rate; not the amount of air between the grinds.
Promote an Even Extraction
Tamping should create a bed of coffee with even density. Even density means there’s no shortcuts or ‘easy ways through’ for the water.
You really want the water to flow through the entire mass of grinds as evenly as possible. Water is dumb, it takes the easy route. If there’s an area of lower density, the water will travel through it more quickly. The grinds in that area will be over extracted and the rest will be under extracted.
To achieve even density we need a perfectly flat, horizontal bed of coffee. Flat tampers are crucial here. If you have a curved tamper, throw it out and buy a flat one. And of course your tamping technique should always be perfectly horizontal.
The amount of pressure applied should be as small as possible, without sacrificing any of the above. Repetitive strain injuries are too common amongst Baristas, so aiming for the lightest pressure that works is key.
You want to control the flow rate of your espresso by adjusting grind size, not tamping pressure. If tamping pressure is a variable then you need to do it the same every single time. This is, frankly, a ridiculous ask for a human and should be entirely avoided. Luckily, there’s an easy way to almost eliminate tamping pressure as a variable.
Tamping squeezes the air from between the grinds. There’s only so much air in there, and eventually the grinds can’t compress any further. At a certain tamping pressure, you’ll hit ‘maximum density’. At this point, the grinds are fully compressed (on the vertical axis). No matter how hard you try, they won’t move any further. Coffee beans are super tough. You can’t crush or damage them with a tamper because the load is distributed across millions of particles.
This is great news for consistency and ergonomics, because:
1) There’s no maximum tamping pressure. You can’t overdo it. Hercules can’t overdo it. The only thing you can do is approach maximum density. Once you’re there, the job is done.
2) Maximum density doesn’t require much pressure.
To find out how little pressure is required try slowly increasing the pressure you apply with the tamper. At maximum density, the tamper will stop moving. If you keep applying pressure, it won’t move any further.
When the tamper stops moving, that’s when you stop pressing.
Why You Shouldn’t Tamp Any Lighter
As I mentioned earlier, you don’t want to rely on tamping pressure as a variable because humans aren’t consistent.
If you tamp lighter, it’s almost impossible to do so consistently. Slight changes in pressure will result in drastic changes to density (and hence, flow rate). The only way you can wipe out this human error is by achieving maximum density. Here’s a little graph to explain:
If it’s lighter than you’re used to, great! Enjoy a healthier barista life.
If it’s a bit harder than you’re used to, great! Enjoy the tasty benefits of consistent density.