What is chill filtration?

Chill filtration is an optional process during the production of whisky, in which the whisky is chilled to a low temperature of around -4o to 4o degrees. This causes any perceived impurities such as fatty acids, proteins and esters to clump together, making them easier to remove. The whisky is then filtered through a special metal mesh to remove these substances.

Why are whiskies chill filtered?

Whisky can naturally become cloudy if it is stored at room temperature for a long time, or if cold water or ice is added. An alcoholic level of below 46% abv., can also make the liquid more prone to hazing. This is a common phenomenon, and a result of flocculation - where these small particles form larger particles. Therefore, some distilleries chill filter their whiskies prior to bottling to maintain the crystal clear appearance of the whisky.

Why is 'free from chill filtration' preferred?

There are many that believe that whisky should be presented as pure and unadulterated as when it is first decanted from the cask. Chill filtration is a process undertaken for entirely cosmetic reasons, with no advantage to the taste. Some think that the process may actually alter the taste of the whisky, and would rather not have anything added or taken from the whisky post-maturation. Fats and oils add to the flavour of whisky, and influence the texture and mouthfeel to be thicker and oiler - all of which would be removed in chill filtration.

Another reason why some prefer non-chill filtered whisky is that the process is a rather modern invention, which is at odds with traditional whisky making. To some, chill filtration is an extra step that compromises the natural, age old process of whisky making. Simply put, whiskies which are free from chill filtration are seen as more authentic. This is why you will often see the words 'non-chill filtered' displayed proudly on bottles of whisky, like a badge of honour. Indeed, on the distilleries end, a big advantage is that skipping this additional step shortens the production process and reduces the cost.

Why was chill filtration invented?

A tale that is often told about the origin of chill filtration goes like this. Just after World War II, a big delivery of Scotch was shipped to America from Scotland in the middle of an especially cold winter. When the cases were unloaded and inspected, a local importer noticed that the whisky was cloudy and rejected the load. He thought that the bottles were impure, or had spoiled during the journey, and so the shipment was returned to Scotland. The whisky had merely chilled to a temperature common during chill-filtration and so the oily elements in the whisky had formed a cloudy haze. Although, it was perfectly drinkable and was the same as they had always made it. However, to save their reputation and ensure that the fiasco never happened again, they began to chill-filter their whisky to ensure the liquid is kept pristine no matter the environment.

Which whiskies are free from chill filtration?

It has become a remarkably common practice in recent years. Distilleries who do not chill filter their whisky often bottle at above 46% abv., which ensures little to no clouding - perhaps only if ice is added. Bunnahabhain is famously adverse to chill filtration, and was a trailblazer of the practice. Ian MacMillan, master blender of the then Burn Stewart Distillers’, and had the idea to raise all of their whiskies' abv level, and impose non-chill filtration. As a result, he says, Bunnahabhain's more robust character came to the fore, and Deanston regained its honeyed sweetness. Simply put, if you are looking for a non-chill filtered whisky, a product will be more likely display this fact than not.