We know even extractions taste great. They’re all signal and no noise. But we’re foiled by a number of factors across green, roasting, and brewing. For this, I’d like to assume that the green coffee and roasting is as even as they can get, and focus just on the brewing.
This is a little question/thought experiment I’ve been rolling around in my head this week (there’s no conclusion, but perhaps it’ll let you in on what I do with spare brain cpu cycles.)
How could we achieve a perfectly even extraction?
Without green and roasting we’re left with two pain points: grinds and brewing dynamics. Even with a perfect roller mill giving us a nice even particle size, there’s still massive discrepancy between the finest grinds and the median size particles. So we have to push further and use only the tiniest grinds.
Obviously, brewing with just superfine grinds would be nearly impossible: complete extraction would take seconds, but filtering it would take forever (at any pressure). An annoyingly perfect paradox.
Here’s where my thinking has lead me:
What if we mix a substance into the superfine grinds that mimics larger grinds? It could be ~100-500 microns in diameter: something to hold all the grinds apart, and allow water flow without altering flavour. After some digging it turns out that this kind of thinking is pretty common in pharmaceuticals and agriculture: they would call it reducing bulk density.
Bulk density is the weight of particles divided by the volume they occupy.
eg. un-tamped espresso grounds have a lower bulk density than tamped ones because they occupy more volume but have the same weight.
For soil, a lower bulk density is advantageous because it allows for more water and air movement between soil particles (see where I’m going here?!). A compacted or super sandy soil can reach a point where the bulk density inhibits water flow and root growth (tamping and 9 bars of pressure anyone?). This is precisely why finer grind sizes create slower flow rate.
So what kinds of materials could we use?
First off, it’d have to be food safe, non-flavoured and generally inert. It’d also need to be more irregular than, say, spheres that wouldn’t hold the fines in a nice matrix.
My first thought was ferritic stainless steel shavings though this sounds expensive and potentially corrosive/flavour altering. They would have the added bonus of being retrievable with magnets for reuse.
The second substance I came across was diatomaceous earth
: the fossilised remains of prehistoric algae. They’re mainly silica, come in sizes from 1-1000 microns, are used for water filtration, and are safe for human consumption.