Filtration is common in a majority of spirit, beer and wine production for the commercial market. Historically filters such as sand, charcoal, felt and animal skins, were used to remove sediment. Chilling the spirit is a technique preferred and used almost exclusively by the whisky trade.
The process of chill filtering is where substances in the whisky are removed before bottling. The main reason to chill filter a whisky is actually 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 to this by removing the offending particles from the whisky, so that this does not occur. 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 forming.
What causes cloudiness?
Cloudiness is caused by the presence of natural fatty acids, esters and proteins in the whisky. These all occur naturally during the distillation process, but some are also imparted from the casks during maturation. When the whisky is cooled, these fatty acids, esters and proteins clump together to give the cloudy effect. A whisky that is not chill filtered is also likely to develop sediment in the bottle if stored in a cool place. Both cloudiness and sediment are seen as undesirable characteristics by the wider whisky drinking audience. During the early 20th century, it was realised that these perceived 'faults' could be 'fixed' by chilled the whisky down. The result was that these elements could be removed 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 tightly knit metallic meshes or paper filters 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.
Good or bad?
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 final flavour. Those against it are convinced that the removal of the natural fatty acids, esters and proteins must alter the aroma, flavour and characteristics, leaving you with a diluted and inferior 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. The argument continues ...