Burr mill
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A burr mill or burr grinder is a device to grind hard, small food products between two revolving abrasive surfaces separated by a distance usually set by the user. The grinder may be powered electrically or manually.
Devices with rapidly rotating blades which chop repeatedly are often described as grinders, but should be distinguished from burr grinders. Burr mills do not heat the ground product by friction as much as blade grinders, and produce particles of a uniform size determined by the separation between the grinding surfaces.
Food burr mills are usually manufactured for a single purpose: coffee mills for coffee beans, pepper mills, mills for coarse salt, spice mills. Coffee mills are usually powered by electric motors; domestic pepper, salt, and spice mills, used to sprinkle a little seasoning on food, are usually operated manually, sometimes by a battery motor.
[edit] Coffee grinders
The uniform particle size is desirable for the specific case of coffee preparation by any of the various methods. Some methods may be more tolerant of a range of sizes produced by a blade grinder; this may be the case for drip (percolated) and French-pressed coffee.
Manual coffee grinders have been supplanted by electrically powered ones where the object is simply to get the job done; manual grinders are used more for their "traditional" appearance: they are made to look good, and are often more costly than the cheaper electric models. An exception is the manual Turkish coffee grinder; these are inexpensive, and can grind coffee to fine powder for Turkish coffee, unlike the cheaper electric models.
Many grinders are free-standing; some larger coffee grinders are fixed to a wall.
[edit] Manual burr grinders
Manual burr grinders are turned by hand, rotating one grinding surface against the other. Coffee mills usually have a handle, providing leverage for the many turns required to grind enough coffee for a cup. The ground coffee is collected in a container which is part of the mill.
Salt, pepper, and spice mills, essentially the same as coffee mills, usually do not have a handle, the entire top rotating instead. While this is less convenient, only a few turns are required to grind enough. The ground product falls directly onto the food being seasoned; the mill has no container. A few mills have abrasive surfaces which do not rotate; each squeeze of the handles moves one flat plate past another, then the plates are restored to their original position by a spring. Many hard spices are available in containers incorporating a simple cone burr grinder, intended to be discarded when empty.
Most grinders can be adjusted to set the fineness of grind.
Manual mills can be used for grinding other food products than they are intended for. Be aware that mills designed for pepper grinding are inappropriate for grinding flour. However, coffee mills are a suitable substitute. For example, Laura Ingalls Wilder's novel The Long Winter describes a family taking turns at grinding wheat in a coffee mill to make flour during months of hardship.
[edit] Electric burr grinders
Electric burr grinders are powered by electricity from a battery or mains supply. An electric motor drives the grinding elements against each other. Electric grinders grind faster than manual grinders with no effort, but heat the ground product a little by friction.
