Cleaning and Polishing

We mentioned earlier that the 'tasty stuff' in flavored spirits such as rum or whiskey is derived from congeners present in the fermented mixture. Unfortunately, the congeners are not very pleasant when fresh - in fact, they can be downright horrible or even poisonous! These congeners include fusel alcohols (from the German "Fusel", or "bad alcohol"), oils and volatile esters. Some of these substances contribute nicely to flavor and bouquet, but most do not. Some of them are the major source of hangovers!

Carbon treatment of raw spirit can remove many congeners, both the pleasant and the unpleasant ones. Many brands of commercial spirits are filtered through charcoal, or stored in charred wooden barrels, often with the claim that this produces a better-tasting product.

Chemists have discovered quite a bit about the manufacture and use of activated carbon for adsorbing chemical contaminants, and we can use this to profitably. (Note the word adsorption, not absorption. Absorption is what sponges do when water is carried bodily in the holes inside the sponge. Adsorption is where individual molecules of a contaminant are held onto the inside surface of the porous carbon by electrostatic attraction or by loose chemical bonding).

Activated carbon products are carefully designed for their end use, and manufactured in a process which involves careful selection of ingredients, very high temperatures and gas or steam treatment. They work by physical adsorption of contaminants onto the enormous internal surface area of the carbon, typically 1,000 square meters (a quarter of an acre) per gram (hard to believe, but true!). Remember, it's a physical and not a chemical effect that makes them work.

It pays to be very careful in choosing the source and type of activated carbon you use to clean spirits. Aquarium carbon will not do! This is a cheap mixture of many sorts of charcoal that may remove some of the congeners from the spirit, but can also introduce nasty trace elements and flavors of its own. Fish don't mind, but you will! Properly made activated carbon is on the market now, specifically designed for the purpose of cleaning spirits - a process called polishing. More information about activated carbon is in Appendix 4.

Removing the contaminants is a rapid and effective method of dealing with congeners, but one that produces flavorless spirits. These spirits are usually then mixed with flavorings to produce a wide variety of beverages

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