Islay whisky making
Distilling on Islay Milling
To prepare the grains for fermentation and expose the sugars within, the malt is broken up by milling into grist.
There are a variety of different designs of mill available, but as most distilleries use a coarse grist, they use a mill with two sets of rollers: one to crack open the husk of the grain and start to break up the internal structure, and a second to further break down the endosperm.
The milled malt is classified in three different grades based on size. From largest to smallest, these are generally known as husks, grits/middles and flour. To measure the make-up of the grist, a sample will be run through a screening machine. These vary in complexity from fully automated devices down to a set of three boxes separated by differently sized meshes, but the theory is the same – the sample is placed in the top, and divided into the three grades by shaking, with larger particles unable to pass through a mesh at each stage.
Managing the ratio of the grades is very important, as each plays a role in successful mashing. The husks help to filter the mash, and while flour allows easy sugar extraction, it can block the filtration plates in a mash tun. Most distilleries use a ratio of around 70:20:10 grits:husks:flour, with small modifications made from location to location based on individual production processes.
FACT: 6 Islay distilleries use mills made by Porteus
FACT: Ardbeg’s Boby mill is the oldest working mill of its type in the world