Chill filtration is the process where substances in the whisky are removed before bottling. The main reason to chill filter a whisky is purely cosmetic. A non- filtered whisky that is 46% ABV or lower will go cloudy when water or ice is added and when the whisky is cooled. This is seen as undesirable by some consumers and the distillers react by removing the offending particles from the whisky, so that this doesn’t happen. The distillers 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 in the whisky. These occur naturally during the distillation process and are also imparted from the cask during maturation. When the whisky is cooled, these fatty acids, esters and proteins clump together to give the cloudiness. A whisky that is not chill filtered is also likely to develop sediment in the bottle if stored in a cool place. 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, then these elements could be removed more easily.
The process of chill filtration involves dropping the temperature of the whisky to zero degrees Celsius in the case of single malts and -4 degrees in the case of blends. The temperature for blends is lower as they contain grain whiskey and these have a lower natural concentration of the fatty acids. Once chilled, the whisky is passed through a series of metallic meshes under pressure. The amount of residue collected depends on the number of filters, the pressure used and the speed with which it is done. The slower a whisky is passed through the filters at a lower pressure, then the more residue will be collected but this is also more costly. During this process, any other sediment or impurities from the cask (called ‘coals’) that are present will also be removed.
The subject of chill filtration is a current hot topic in the whisky industry. It is looked upon badly by some, as consumers demand more natural or organic products in all areas of their lives. The other contentious issue is whether chill filtering a whisky affects 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. In reality it is difficult to compare as no one releases the same whisky in a chill filtered and non chill filtered form.