Grind consistency: Four grinders put to the test

Gold plated coffee grounds…hand grinders that work as well as commercial machines…”bimodal grind size distributions charts”…There’s a lot of intriguing science behind coffee grinders these days. Many specialty shops are experimenting with a variety of grinders to see what really gives the best product. True to form, grinder manufacturers are upping their game as well, with the result that coffee freaks can choose from a huge range of grinders specific to what they’re making and how they’re making it. Are you the owner of a busy specialty shop that sells mostly espresso? There’s a grinder for you. Are you a tea drinker that only brews a cup of coffee once in a while when you’re feeling frisky? There’s a grinder for you.

Here at Machina, we’re geeky about grinders and we thought it would be interesting to put four very different grinders to a simple, yet informative test. So, we stuck some coffee under the microscope to check out grind consistency.

Why is grind consistency even important? Because when you’re timing your drip coffee or espresso pull, each bean particle will be immersed in water for the about the same amount of time—that means that in order to decrease over-extraction of some particles and under-extraction of others, you want the particles to be similar in size (think surface area) so that they all extract as evenly as possible. Think of it this way: if you boil an ostrich egg and a pigeon egg for exactly four minutes, the pigeon egg is likely to be way overdone, while the ostrich egg is likely to be underdone. Now if you boil two chicken eggs for four minutes, you’ll have two perfectly-cooked eggs. With everything else held constant, particle size consistency will affect the end result for better or worse.

For this mini-experiment, we tested the Tiamo hand-grinder, the Mazzer Major, the Ditting KR1203, and the Hausgrind by Knock hand grinder. Just two caveats before you check out the pictures:

1. These are under 40x magnification of a Zeiss light microscope. Light scopes are made for looking through thin layers of transparent things. Since we’re trying to look at three-dimensional objects in a two-dimensional plane, the photos are a bit blurry. Bear with me.

2. These grinders are not set to the same size—they’re on whatever size we were using in the shop that day. That doesn't affect quality comparisons; just remember you’re looking at consistency within samples.

May the sampling begin...

Tiamo: Ceramic conical burr hand grinder

A bit of a sparse sample, but you get the picture. Lots of different sizes and fairly irregularly-shaped; but for a budget-conscious home hand grinder like the Tiamo, it’s not bad at all.

Mazzer Major: 83 mm flat steel burrs

Here’s a good example of bimodal size distribution in particle size; note the large square particles and the tiny fines. The fines are an inevitable part of grinding and are also thought to be important in holding together the espresso puck during percolation. The large particles are very consistent in size and shape. Way to go Mazzer.

Ditting KR1203: 120 mm flat steel burrs

There were a lot of air bubbles in this shot, but you can clearly see the strange shapes of these particles. Some are large, some are small, some are round, some are irregular and ribbon-like. Not particularly consistent…

Knock Hausgrind Hand Grinder: 38 mm conical steel burrs

What do these pictures remind you of? If you said the Mazzer Major E, you win a flat white. These have a similar bimodal size distribution as well as unbelievable size and shape consistency of large particles—all from a hand grinder! My hat’s off to Knock for their beautifully-designed grinder.

For a little more grinder nerdery, check out an excellent post using a scanning-electron microscope on gold-plated coffee grinds here, or a very thorough study of grind size by Orphan Espresso here.