One of the biggest problems when describing a brewing method is getting across what size of ground coffee to use. The trouble is that each grind setting on a coffee grinder will produce a range of sizes rather than one exact size.
How coffee grinders work
The reason we get a range of sizes from a grinder, is that grinders use a crushing action to break the bean into smaller pieces. On a conical burr grinder, there are two discs: a female cylindrical disc and a male dome shaped disc. Each disc has ridges (know as teeth) running across its surface, and it’s these ridges which crush the bean. Obviously crushing isn’t an exact science. Irregular sized pieces break off from the bean each time it’s crushed between the grinder’s teeth.
If you look at the cross section below of a burr grinder: the bean enters at the top and as it progresses down, the gap narrows between the two discs, breaking the bean into smaller and smaller pieces. The ground coffee cannot escape from between the grinding discs until it’s small enough to fit through the gap at the bottom (indicated by the two red arrows).
When the grinder is adjusted to a finer setting; the male disc moves up in relation to the female disc narrowing the gap.
Therefore, each grind setting only sets a maximum limit for the size of the coffee grounds. There’s nothing to stop much smaller grounds passing through the gap. So the range of grounds can be anywhere between a tiny pin prick to the maximum limit set. For this reason, a fine grind setting for espresso will have a much smaller variation in size than a coarse grind setting for a cafetiere.
So how do you communicate grind size?
As we can’t simple say something like: “grind your beans until they are 1.2mm in length”, we have to come up with something more inventive. Photos of grounds are great (see below), but they have no scale to them. To help get round this we try and make comparisons to other things we find around the house: “your grind should be similar in size to granulated sugar”. But it still leaves it a bit ambiguous.
I’ve come up with an idea; a geeks approach to communicating grind size. I’ve taking a close up picture of a range of grounds in each grind setting. But then adding scale to the picture. If you look at the two pictures below, the one on the left is for a cafetiere and the one on the right for a stove-top coffee maker. Each red line represents 1mm.
Cafetiere grind on left. Stove-top grind on right.
Obviously the photos could be better (the cafetiere one is a bit devoid of grounds). So it’s still a work in progress, but I would love to know what you think about this idea. Whether this helps get the message across?
Tags: cafetiere, coffee grinder, espresso, stove-top
