There are two main types of machines used to grind coffee beans: blade bean grinders and blade grinders.

Blade grinders are simpler and much less costly and expensive than blade grinders. They use sharp blades to chop up coffee beans, and the grind size gets smaller as the blades spin longer, meaning the grind is usually related to how long the blades keep spinning. (It's the kind of food processor that can grind not only ground coffee, but also ground green beans, ground red beans, and, with a different blade, ground meat.)

Blade grinders aren't usually particularly precise, because it's hard to control the grind this way and it's difficult to maintain consistency. When extracting coffee, all that's desired is for the particles to be distributed as evenly as possible, so repeatability, precision, and consistency are all important.

Blade grinders, by contrast, are much more precise. They grind coffee between two raised metal disks. The grind is determined by the distance between the two discs - the closer they are, the finer the grind, and vice versa.

Blade grinders allow for precise adjustments, while blade grinders usually do not. This allows coffee enthusiasts to better choose the grind, which gives them a better chance of extracting flavor from the ground coffee in an even and consistent manner.

The most important thing for coffee lovers is the consistency of the grinder. A blade grinder grinds a more even and consistent ground coffee, and this consistency makes a huge difference in the quality and flavor of the extracted coffee.

What kind of grinder should I choose?

While blade grinders are the clear winner, not all blade grinders are created equal. From the shape to the size and material, they vary greatly.

Shape

Blade bean grinders come in two main shapes: flat blade and tapered blade. There is an ongoing debate about which one is better.

Hand-cranked mills often use conical blade discs, while flat blade discs are more favored by manufacturers of high-quality electric bean grinders.

These two types of blades work in slightly different ways, but overall, the results are similar. In general, flat blade discs are more expensive and more stable, while conical blade discs are cheaper and less noisy.

Size

Bean mill blades come in a number of different sizes. This measurement is usually given in millimeters (mm), which is the diameter of the largest blade.

Domestic electric bean grinders usually have a blade that starts at around 40 millimeters, while commercial models start at around 60 millimeters and can go up to 100 millimeters or more. As the size of the blade increases, so does the size of the bean mill itself. In general, the larger the blade, the better the performance, more consistent, faster, more efficient and usually requiring less grinding adjustments.

Calibration and Precision

Calibration and precision are equally important for bean mill blades. If the blade is not precisely calibrated, then the perfect grind size will become more difficult to achieve.

Precise calibration is mandatory in order to achieve good particle distribution. This is even more important with larger cutter disks.

If there is too much space between the cutter disks, it is impossible to get a perfect particle distribution. The extraction of smaller and larger particles is not the same, and if the particles are too different, under-extraction and over-extraction can occur at the same time, making a well-balanced cup of coffee difficult to achieve.

Materials

The blade of a bean grinder is usually either metal or ceramic. Metal blades are more durable, more expensive, and usually more accurate; while ceramic blades are better at dissipating heat.

Try to avoid ceramic blades; while they're cheaper and they do grind coffee, ceramic teeth are usually less sharp and tend to wear out. They create excessive dust, which affects particle size and distribution, creating a "muffled" flavor.

Some grinders have interchangeable blades made of different materials. Metal blades are usually made of steel, while regular steel is relatively easy to cut, but they can oxidize and rust. To make the blade last and stay sharp, it should be hardened by heat treatment or coated with a harder substance (such as titanium).