The whole tea leaves are ground, also known as milling, to facilitate the brewing process.
The fineness of the grind strongly affects brewing. Brewing methods that expose tea grounds to heated water for longer require a coarser grind than faster brewing methods. Leaves that 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 tea unless more is used. Due to the importance of a grind's fineness, a uniform grind is highly desirable.
If a brewing method is used in which the time of exposure of the ground tea to the heated water is adjustable, then a short brewing time can be used for finely ground tea. This produces tea of equal flavor yet uses less ground tea. A blade grinder does not cause frictional heat buildup in the ground tea unless used to grind very large amounts as in a commercial operation. A fine grind allows the most efficient extraction but tea ground too finely will slow down filtration or screening.
Ground tea deteriorates faster than whole leaves because of the greater surface area exposed to oxygen. Many tea drinkers grind the leaves themselves immediately before brewing.
There are four methods of grinding tea for brewing: