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Malt Milling
(selected excerpts)The object of milling is to split the husk, preferably lengthwise, in order to expose the starchy endosperm for milling and allow for efficient extraction and subsequent filtration of the wort. However, it is necessary to compromise between the requirements for extraction and filtration because although a fine grind potentially yields more extract, it can lead to subsequent filtration problems and a loss of extract in the spent grains. In addition, excessive fine milling may lead to increased wort viscosity due to enhanced beta-glucan extraction (2). Furthermore, it may cause "balling" of the grist, which is the formation of clumps of malt that are wet on the exterior but dry inside. This will result in a loss of extract recovery since the grist is not converted during the mashing process.
Malt milling is usually done by either dry or wet milling. The selection of the type of milling and employment of a brewery-specific milling process is determined by the size distribution of malt kernels, their modification, moisture content, the mashing methods, and the wort separation method. For example, the degree of modification must be considered when milling. Poorly modified malts require fine grinding and well-modified malts can be more coarsely ground. Quality and uniformity of the crush is more important for an infusion mash than for a multi-temperature mashing program. Measurement of the particle size distribution of a grind is done by using a standard brewery sieve analysis.
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