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Coffee Grinders

Grinder Qualities

Grind Consistency

The main goal of a grinder is to produce particles of consistent size profile while applying minimal heat to the bean.
Other factors are more a matter of convenience.
It's important to realize that consistency doesn't mean that all particles are of the same size.
Instead there's a small range of particle size, or even several ranges.
The best grinders will produce a narrower band, meaning the particles will be pretty close, but not exactly the same size.
To complicate matters, in espresso grinders, the ideal is to produce two sizes of particles: the smaller "fines" are thought to hold the puck together.
The best espresso grinders show two peaks or bands, so that most of the particles are of two sizes, with a small amount of particles in between those sizes.
A grind profile is a graph that shows all the particle sizes taken into account.
It's important to realize that the different sized particles infuse differently, and this allows different parts of the coffee to come out in the cup.
It's the overall profile that's responsible for how the particles infuse in water, and therefore how the coffee tastes.

Particle Size

Other Factors

  • adjustment of grind sizes
  • amount of grinds retained inside the grinder after use
  • static electricity
  • doser vs doserless
  • noise
  • cost

Types of Grinder

Mortar & Pestle

A lot of work.
Very difficult to create a consistent grind.

Hand Mill

Hard work to grind in any quantity.
Some small hand held grinders are very difficult to hold onto while grinding.
The burrs in some, but not all, hand mills are spring-loaded, which can allow the burrs to shift, resulting in an inconsistent grind.
These spring loaded burrs tend to be better when there's less play, and therefore produce a more consistent grind on the finer side,and a less consistent coarse grind.
Other hand mills hold the burrs on a screw or some other stable mount, resulting in a more consistent burr alignment, and a more consistent grind over the range.
Without a motor, and the resulting high torque and forces, these are very cheap to make, so you can get a quality burr at low cost, resulting in the best grind for the money.

Blade Grinder

Blade grinders fracture the bean by impact instead of crushing.
The speed at which the blade operates causes the beans to heat up, which impacts the flavor.
It's impossible to get a consistent grind from a blade grinder.
It is possible to improve the consistency by running it for a long time, but this increases the heat applied to the coffee, and there's no way to adjust the resulting very fine grind size.

Burr Grinders

Burr grinders apply pressure to the beans resulting in stresses that fracture the beans.
They operate in stages, crushing the beans finer at each stage.
A flat grinder has a smooth curve with a varying radius--a circle that gets smaller as you move across the burr.
At the outer stage, a larger curve crushes the beans to a larger size, allowing the pieces to fall through to a spot with a smaller radius that crushes them further.
Conical grinders are often designed with several distinct stages.

Cheap Burr Grinders

Cheap burr grinders tend to have problems with heat and grind consistency.
The burrs themselves are small, so heat builds up more quickly and more intensely. That heat is transferred to the bean, affecting the cup.
The precision and sturdiness of the mountings are often of lower quality, resulting in a less consistent grind.
The burrs themselves also tend to be of lower quality due to cost cutting.
Finally, a less powerful motor with less torque needs to be operated at a higher speed to compensate for the lack of power, and that speed translates to even more heat.

Espresso Grinders

The ideal espresso grinder creates two different sized particles.
Some say the finer particles help to hold the puck together.
The key factor is that the particles are a consistent size, but in this case there are two size groups.
The ability to make minute adjustments to the grind size is especially important in an espresso grinder.
Many of them are stepless, allowing adjustments to be made continually, rather than in small "notched" steps.

Flat vs Conical Burrs

There's quite a debate between these types of burr.
There's a difference of opinion on which produces a more consistent grind, as well as which type is more expensive.
The key differences:
Forces
Conical burrs impart most of the force to the outside of the burr.
In essence, the forces are applied onto the outside burr.
Since the ouside burr is solid, you only need to hold it centered and aligned for it to work properly.
The forces on the mounting are minimal, so the mount doesn't need to be as solidly built.
It does, however, require more precise positioning to hold the burrs perfectly flat, centered, and to maintain the distance.

Flat burrs impart force upward.
This transmits all the force to the burr mountings.
This requires a heavy duty mounting able to withstand the force while keeping the burrs perfectly aligned.
Flat burrs must be held perfectly flat relative to each other, while maintaining the distance between the burrs under heavy force,
but otherwise don't need to be aligned.
Price
There's some difference of opinion on which type of burr grinder is more expensive.
It really comes down to what level of quality you're going for.
Perhaps it's easier to build a grinder with flat burrs, but more expensive to design a stable mount for them.
Speed
Flat burrs oscilate faster than conical burrs.
The extra speed might impart more heat to the beans.
In practice, it's quite debatable whether this actually transfers heat to the beans.
Consistency Over a Range
When you compare individual grinders, there's no clearcut advantage of one type of burr over the other: the overall design of the grinder,
including burrs and mounting, is the most important factor.
But there does seem to be an overall tendency that has something to do with how the different types of burr work.
At espresso sizes, conical burrs tend to produce a more consistent grind profile (i.e. 2 distinct particle sizes).
If conical burrs tend to excel at finer settings, they tend to lose out to flat burrs at coarser settings.

Grinds for Different Brewing Equipment

Arabic/Turkish/Greek Coffee

Arabic coffee is made of only the finest particles, almost a powder.
These wet fines tend to form a muddy sludge that makes the grinds stick together and settle on the bottom.
The "boiling" also helps to push the grinds together, and is important to making a clean cup of coffee.

Espresso

Espresso requires a very fine grind, with a small amount of even smaller fines.
You don't agiatate the grinds at all in espresso, so the fines stay suspended.
Wet fines tend to produce a sort of muddy sludge, which helps to keep the puck together.

Filtered Coffee

Whether you're making Cowboy coffee, drip, or press, you want to remove the grinds from the brew before drinking.

At the grossest level, you can just let the grinds settle to the bottom of the cup.
This can work well for very consistent grinds. Very coarse grounds will settle due to gravity.
In the special case of Arabic or Turkish coffe, the very fine grinds accumulate and cake up on the bottom of the cup.

In a press pot, you have a relatively coarse filter that removes coarse particles.
Finer particles will end up in the cup, so you want to limit the amount of fines produced.
As indicated earlier, espresso grinders in particular are designed to make a certain amount of fines.
In addition, many grinders operate better at fine settings.
The result is that the ideal grinder for press coffee isn't necessarily the best grinder for other types of coffee.

Paper filters have a much finer mesh made up of paper fibers. This all but eliminates any detectable particles.
The trick here is to prevent the finest dust from clogging the fibers.
In a normal burr grinder, most of the small particles will be trapped among the larger particles.
While this is important in making espresso, there's little opportunity for the particles to separate in a puck of espresso.
That's not the case with paper filtered coffee.
With paper filters, you want to avoid stirring or agitating the grinds too much, because this allows those fines to separate and clog the filter.

Other Methods

Most other methods seem to fall into one or more of the above categories. In terms of the grind, a percolator is a type of filtered coffee. The aeropress uses a paper filter with the additional requirement to form a puck under a bit of pressure. The moka pot has both filter and puck. The exact grind size depends on very minor factors, such as the quality of paper or the size of the filter mesh, so you'll have to experiment a bit with any method to get it just right.

Grinder Reviews

See Also

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