Exploring the vital role of refrigeration in whisky production processes.

I have to confess I am a bit of a failure as a stereotype of the Scottish male. I can’t play the bagpipes, I don’t do golf, and I have never been to a professional soccer game in my life, despite being born and bred in a city famous for the intense rivalry of its two teams—on a par with Madrid, Manchester, or Milan. Until recently I was not a whisky drinker either, but getting older brings some compensations, including developing a taste for olives and fine whisky, although not together

Whisky (note no “e”) is the single largest export in the Scottish economy and has spawned many famous brands. The name is simply the Gaelic word for “water,” but is shortened from uisge beatha, which means “water of life,” aqua vitae in Latin or vodka in Russian. It sounds like there is a lot of denial in this area, so best move on. Whiskey (with an “e”) is the equivalent product from Ireland, Tennessee, and other places and has its own fans. At the Purdue conference on refrigeration last year, delegates were given a sample bottle of “Indiana Whiskey,” which carried on the label the proud boast “Aged 6 months.” The delegate pack also included a box of toothpicks, but I don’t think this was a comment on the quality of the drink.

The link between whisky and refrigeration is not as obvious as it is for beer (in last month’s column), since the distillation of the spirit is done at temperatures easily achieved with river water or cooling towers. However, many other parts of the production process benefit from the science of refrigeration. One of the more unusual requests we have handled over the years was for a plant to chill and then reheat the whisky in a bottling plant. This was done in a three-stage heat exchanger, like a milk pasteurizer in reverse. The second stage used refrigeration to chill the whisky to 39°F (4°C) before passing it through a filter. It was partially reheated in a heat exchanger, which also provided the first stage of prechilling, and then was heated back to room temperature with waste heat from the refrigeration system.

We owe grateful thanks to the great American whisky drinking public for making this complex process necessary. The popularity of scotch on the rocks is the reason. Distilled whisky is mainly ethyl alcohol but also contains some longer chain hydrocarbons. These become waxy when chilled by ice cubes, so the filtration process is designed to remove these waxes in case they cause consternation in the drinker, who might otherwise think his drink was cloudy because his eyesight was failing. The reheat stage was found to be necessary because otherwise the bottles, when filled with chilled whisky, became wet from condensation, and the labels wouldn’t stick to the glass.

Another novel use of refrigeration in the whisky business was in response to the problem of “the angels’ share.” This is the result of alcohol having a higher vapor pressure than water, so about 2% of the alcohol content of whisky that is maturing in a barrel evaporates each year. Compound interest on this grab means that if the spirit is 60% proof when it goes into the barrel, it will be less than 40% if it is aged more than 20 years. To be classed as a single malt, the final product must be at least 40% proof and must have nothing added to it once it is laid down, so it can’t be topped up with neat ethanol. The solution to this puzzle, to enable older whiskies to keep their single malt classification, was to freeze some of the water in the matured spirit and then centrifuge the ice out. This enabled the alcohol content of the remaining drink to be kept above the threshold, greatly increasing the value of the bottled product. Thank you, refrigeration world, for keeping old drinkers happy.