An old-fashioned manual burr-mill coffee grinder.
An old-fashioned manual burr-mill coffee grinder.
The whole coffee beans are ground, also known as milling, to facilitate the brewing process.
The fineness of grind strongly affects brewing, and must be matched to the brewing method for best results. Brewing methods which expose coffee grounds to heated water for longer require a coarser grind than faster brewing methods. Beans which are too finely ground for the brewing method in which they are used will expose too much surface area to the heated water and produce a bitter, harsh, "over-extracted" taste. At the other extreme, an overly coarse grind will produce weak coffee unless more is used. Due to the importance of fineness, uniformly ground coffee is better than a mixture of sizes.
If a brewing method is used in which the time of exposure of the ground coffee to the heated water is adjustable, then a short brewing time can be used for finely ground coffee. This produces coffee of equal flavor yet uses less ground coffee. If the coffee is ground by a less than high end grinder such as the blade type which produces a mix of small and large grains then the brewer soon becomes familiar with the average size characteristics of his/her particular machine and adjusts the brewing time and proportions accordingly. A blade grinder does not cause frictional heat buildup in the ground coffee unless used to grind very large amounts as in a commercial operation. A fine grind allows the most efficient extraction but coffee ground too finely will slow down filtration or screening.
Ground coffee deteriorates faster than roasted beans because of the greater surface area exposed to oxygen. Many coffee drinkers grind the beans themselves immediately before brewing.
There are four methods of grinding coffee for brewing: burr-grinding, chopping, pounding, and roller grinding.
Burr mills use two revolving abrasive elements, such as wheels or conical grinding elements, between which the coffee beans are crushed or "torn" with little frictional heating. The process of squeezing and crushing of the beans releases the coffee's oils, which are then more easily extracted during the infusion process with hot water, making the coffee taste richer and smoother.
Both manually and electrically powered mills are available. These mills grind the coffee to a fairly uniform size determined by the separation of the two abrasive surfaces between which the coffee is ground; the uniform grind produces a more even extraction when brewed, without excessively fine particles that clog filters.
These mills offer a wide range of grind settings, making them suitable to grind coffee for various brewing systems such as espresso, drip, percolators, French press, and others. Many burr grinders, including almost all domestic versions, are unable to achieve the extremely fine grind required for the preparation of Turkish coffee; traditional Turkish hand grinders are an exception.
Conical burr grinders use steel burrs which allow them to grind effectively while rotating relatively slowly, usually below 500 rpm, reducing frictional heating of the ground coffee, thus preserving maximum aroma. Conical burr grinders are quieter and less likely to clog than disk grinders.
Grinders with disk-type burrs usually rotate faster than conical burr grinders and warm the ground coffee a little by friction, manual models less than electrical. They are cheaper than conical burr grinders, and are well suited for grinding small amounts of coffee (with no time for heat to build up) for home use.
Coffee beans can be chopped by using blades rotating at high speed (20,000 to 30,000 rpm), either in a blade grinder designed specifically for coffee and spices, or in a general use home blender. Devices of this sort are cheaper and longer-lasting than burr grinders, but the grind is not uniform and will produce particles of widely varying sizes where ideally all particles should have the same size, right for the method of brewing. The ground coffee is also warmed by friction. But any heating effect is negligible if grinding only enough beans for a few cups of coffee by this method because the process is over in less than ten seconds.
Blade grinders create “coffee dust” that can clog up sieves in espresso machines and French presses, and are best suited for drip coffee makers. They are not recommended for grinding coffee for use with pump espresso machines.
Arabic coffee and Turkish coffee requires that the grounds be almost powdery in fineness, finer than can be achieved by most burr grinders. Pounding the beans with a mortar and pestle can pulverize the coffee finely enough.
In a roller grinder, the beans are ground between pairs of corrugated rollers. A roller grinder produces a more even grind size distribution and heats the ground coffee less than other grinding methods. However, due to their size and cost, roller grinders are used exclusively by commercial and industrial scale coffee producers.
Water-cooled roller grinders are used for high production rates as well as for fine grinds such as Turkish and espresso.
What separates cheaper grinders from more expensive ones?
Espresso requires an exceptionally fine grind, and a grinder has to work hard to achieve it. High quality grinders will have a powerful motor, metal gears (as opposed to plastic gears in cheaper machines), and heavy duty burr mounts (so the burrs don’t wobble and vary in speed slightly during the grind, resulting in an uneven process). Grinding for espresso also puts a lot of stress on a machine, so grinders designed for espresso are also built to be more durable.
As a rule for all brewing methods:
the more consistent the grind, the better the flavour in the final cup. With an inconsistent grind, the larger coffee particles underextract while the smaller particles (or “fines”) over extract, resulting in bitter, or “muddy” flavours.
Bodum Bistro Burr Grinder
Capresso Infinity, Black ABS plastic
Baratza Maestro Plus
Capresso Infinity, Stainless Steel
Recommended for espresso on a machine with an unpressurized portafilter:
Baratza Virtuoso Preciso
Any Macap model
Any Mazzer model
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