Liquid solid separation in the brewhouse.

Johnstone, J.

Abstract
Brief descriptions of some of the types of equipment used to separate wort from spent grains, namely the traditional mash tun, the "Strainmaster", the traditional mash filter and its modern developments (high pressure filter, thin bed filter and "Meura 2001"), are presented. The most widely used mash separation device, the lauter tun, is discussed in detail. The importance of avoiding excessive agitation during mashing and mash separation, in order to limit oxygen pickup and the release of viscous gums, is explained. Modern brewhouse equipment includes mash transfer systems which pass the mash slowly and gently from the mashing vessel into the bottom of the lauter tun, using a variable speed pump. In order to ensure the maximum wort output consistent with clarity, the operation of the raking machine must be carefully controlled so as to keep the bed of grains loose enough for rapid wort flow while avoiding excessive disruption which might allow cloudy wort to pass through the bed without being filtered. Control systems for the raking machinery and also to govern the temperature and application rate of the sparging liquor are described. Graphs illustrating the effect of raking on grain bed resistance, wort turbidity, wort flow and oxygen pickup as well as the different turbidity and flow patterns produced by brews of varying grist composition (pure barley malt, mixed barley and wheat malts, and barley malt with maize adjunct) and mash volume are presented. Although wedge wire false bottoms are commonly believed to increase wort flow rates, the author considers this to be an error and claims that slotted plate false bottoms produce a clearer wort. It is pointed out that unlike other mash separation devices, the lauter tun can tolerate considerable variations in the quality and composition of the mash without any effect on processing time.
Keywords : lauter tun mash separation performance process control quality wort