Malt Milling(book excerpts)
The objective of milling is to reduce the malt to small particle sizes in order to expose the starch in the endosperm, which allows the enzymes within the mash to convert the endosperm into sugars. The more extensive the malt is milled, the greater the extract production. However, the fine grind can lead to subsequent wort separation problems and a loss of extract in the spent grains during wort separation. As a result, the brewer needs to consider whether a mash or lauter tun will be used, or for that matter whether a mash filter, and the degree of malt modification. For example, mash tuns require comparatively coarse grists while lauter tuns can use finer grists and mash filters still finer grists. For a lauter tun, poorly modified malt should be milled more finely to give enzymes access to the starch which can be shrouded behind cell wall material which has not been broken down adequately in the malting process. Conversely a well-modified malt can be milled more coarsely to permit faster separation without sacrificing extract performance.
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