It’s the process of cooling an alcoholic liquid down to about -1C and pushing it through a metal or paper filter. It removes certain elements that make whisky look cloudy.
Whisky gets its taste and smell from the compounds it contains, most of which are soluble in the water-ethanol mixture characteristic of all alcoholic drinks. But some compounds are only soluble at certain temperatures.
So when the whisky is diluted with cold water, or simply gets cold enough, molecules clump together to form small particles known as micelles. These scatter light, making the liquid appear cloudy, in a phenomenon known as chill haze. You can only see the compounds, and therefore filter them, when the liquid is cold.
Human perception of flavour is complicated, so some of us will find whiskies less palatable if they’re hazy. It’s difficult to define what’s a true difference in flavour and what’s just perceived. Over the years, this has been debated constantly.
A clearer liquid can be seen as a sign of quality, but some people feel that by filtering out specific compounds, you’re taking away flavour or changing the mouthfeel. In taste tests, non-chill-filtered whiskies are often judged as “fuller”, “rounder” and “richer” than their chill-filtered counterparts.
George Smith didn’t have the option to chill-filter The Glenlivet. These days, we chill-filter most of our expressions – all, in fact, other than the Nàdurra range. Conduct some taste tests of your own, and see what you think.