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Whisky Basics 3: Milling and Mashing

Whisky Basics 3: Milling and Mashing


When the grain arrives at the distillery, it needs to be broken down into grist. Grist is a powder made up of husk, flour, and grits. The first step of milling is destoning, which separates the grain from any stones, dirt or debris that may have found its way into the mix.  There are two main types of mill, the roller mill and the hammer mill. The more traditional mill is the roller mill, and is more suitable for barley as it grinds a coarser grist that can form a filter for the wort. A roller mill pushes the grain through a number of rollers, the first set of rollers cracks open the husk, and the subsequent rollers grind the grain down into a fine flour. Some of the most sought after roller mills are the ones made by Porteus, a British mill maker that made roller mills that were so reliable the company went bankrupt. Sadly making a mill so reliable that no-one needs to pay for maintenance or replacement isn’t a sound business model. These mills are so well known for their reliability, many new distilleries will seek out a Porteus mill (many now over 80 years old) from a mothballed distillery or brewery instead of buying a newly made mill. A hammer mill is more suited for working with mixed grains due to the finer flour created. Modern mashing methods mean that the grain bed filter is no longer totally necessary so a hammer mill is a viable option for modern distilleries that want the option to experiment with grains other than barley. a hammer mill will give you a very fine flower, so should be paired with a mash filter to create a viable wort. A hammer mill works by spinning hardened steel ‘hammers’ in a textured chamber to grind the grain down into a fine flour.


It is incredibly difficult to ferment and distil solids, so the grist has to be mixed with water. This is done in a container called a mash tun. There are three key types of Mash Tun; traditional, lauter, and semi-lauter. A traditional mash tun is usually, open topped, and made from sections of cast iron bolted together. It contains a mechanism known as a rake-and-plough, which is a curved steel arm with comb like teeth, which rotates throughout the tun mixing the grain and water and disturbing the grain bed. The lauter tun was introduced to Scotland in the 1970s from German brewing and quickly became popular. A lauter tun is made from stainless steel and is usually covered by a copper or steel dome. The lauter tun has a perforated floor that acts as a sieve allowing the grain bed to be easily separated from the wort (sugary liquid that goes onto be fermented). The lauter has a set of blades attached to a rotating arm for mixing and agitating the grain bed. On a full lauter tun these blades are adjustable and can go up and down, on a semi- lauter they are at a fixed height and cannot be adjusted. In order to maximise yields, the temperature that you mix the water and grist is of paramount importance. A typical mashing consists of 3 ‘waters’ at 3 different temperatures, each followed by a rest period and then draining of the wort. The first water is called Mashing in and takes place at between 60-66°C, this is the optimal temperature for gelatinisation of starch and enzyme efficiency. The second water is usually around 75°C and extracts even more sugars. The final addition of water is called sparging and is between 85-95°C this extracts the last sugars but also kills the enzymes, the further purpose of sparging is to wash out and clean the mash tun. The sugary liquid that is extracted is called wort, only the strongest worts go on to be fermented, the rest is recycled to be used for sparging and other waters. The wort is then pumped into washbacks for fermentation. Left over grain from the mashing process is called draff, and is often recycled into being livestock feed or fertiliser, although use as biofuel is beginning to become more common.