Chill filtration is the process where some naturally occuring substances in a whisky are removed before bottling. The main reason to chill filter a whisky is cosmetic. A non chill-filtered whisky that is 46% ABV or lower in alcohol strength will go cloudy and hazy when diluted with water or cooled. This is seen as undesirable by some consumers or that there is something wrong with the whisky. The whisky companies react by removing the offending particles from their products so that this does not occur.
The companies want their whisky to be seen as a top quality product. Whiskies above 46% ABV do not require chill filtration as the higher alcohol level prevents this cloudiness from occurring. The cloudiness is caused by the natural fatty acids, esters and proteins that are present and these form during the distillation process with some also imparted from the cask during maturation.
When the whisky is cooled these fatty acids, esters and proteins clump together to give the hazy cloudiness. During the early 20th century, it was realised that this ‘fault’ with the whisky could actually be used to the distiller’s advantage and that if they chilled the whisky that these elements could be removed more easily.
The process of chill filtration involves dropping the temperature of the whisky - this is around 0°C for single malts and -4°C for blends (this is lower as they contain single grain whisky which have a lower concentration of the fatty acids). Once chilled, the whisky is passed through a series of metallic meshes under pressure. The fatty acids, esters and proteins then stick to the mesh filters while the whisky passes through and is collected for bottling. During this process any other sediment or impurities from the cask are also removed.
The subject of chill filtration is looked upon badly by some who want the most natural products possible. Another contentious issue is whether chill filtering a whisky effects the taste. Those against it are convinced that the removal of the natural fatty acids, esters and proteins alters the aroma, flavour and characteristics and leaves you with a diluted product. Those for the procedure argue that the taste and characteristics remain intact and that filtering gives better control to produce consistently high quality whisky.
* Please note / this post has been updated from the original - June 2020.