Scotch whisky milling equipment: the 4 roll mill

The 4 roll mill is by far the most commonly used mill in the Scotch whisky industry. Named after their creators, the 4 roll mills in Scotland’s whisky distilleries are usually either a Porteus mill or a Boby mill. (Famously, both firms made products that were so good they eventually put themselves out of business.)

Inside, the malt flow is controlled by the feed roll. As malt passes through the top rollers, the barley corn is cracked open and the husk is removed. The husk and fine flour are then directed away to bypass the second set of rollers to protect the husk and keep it complete. The second set of rollers are usually set to be a little tighter, which helps to grind the coarse grits from the heavier endosperm into finer particles. 

All the components of the grist (husk, flour and grits) come together below the rollers to leave the mill ready for the next stage of the process: mashing.

Vital for yield efficiency, milling is an important part of the Scotch whisky production process. 

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