A wee dram o’ chemical engineering

As a dark-haired man, I have spent a number of recent New Year’s Eves standing out in the cold just before midnight so I can be the first person into the house. This is my own fault for having married into a family whose Scottish heritage includes the custom of “first-footing,” which dictates that the first person to step into the house after midnight on New Year’s Eve determines the homeowner’s luck for the coming year.

The ideal visitor is a dark-haired man bearing coal, cakes, a coin or whisky (Scotch, of course). My wife’s family prefers the latter.

In an article called “Chemical Engineering of Scotch Whisky,” published last May in The Professional Edge, the magazine of the Association of Professional Engineers and Geoscientists of Saskatchewan, geologist Gary Yeo says that “in a nutshell, whisky is made by distilling beer.”

Like beer, malt whisky is made from malted barley, water and yeast. “Malted” barley is barley which is starting to germinate—a process that converts the starch in the kernels into a soluble form called dextrin.

Germination is begun by steeping the barley in water and halted by drying it in a kiln, traditionally and even today at least partially fueled by peat (party carbonized vegetation from a bog—the ancestor of coal). The aromatic peat smoke, drifting up through a wire mesh floor, gives the malt a distinctive smoky flavor.

The dried malt is then ground and mixed with hot water, which extracts the dextrin and converts it to a sugar, maltose. The resulting sweet liquid, called wort, goes into a fermenting vat with yeast, which converts the maltose to alcohol and carbon dioxide.

The resulting “wash,” about eight percent alcohol, is distilled in a swan-necked copper still. (Copper reacts with sulphur compounds that would otherwise impart an undesirable flavor.) As the wash is heated, the alcohol in it evaporates and is drawn off through the thin neck.

This first distillation extracts about a third of the wash as “low wines,” an oily spirit containing 17 to 21 percent alcohol. This is distilled a second time. The earliest spirits (foreshots) produced during the second distillation and those at the tail-end (feints) have higher concentrations of impurities than the desirable “middle cut.”

Early in the spirit run is where you find the aromatic esters that give desirable fruity flavors. Nitrogen compounds, which give whisky biscuity flavours, begin to appear about halfway through the run. Undesirable sulphur compounds turn up later. The phenols imparted by peat smoke during kilning show up about a third of the way through.

The stillman carefully chooses the middle cut to produce a whisky of the desired character. It’s drawn off as new spirit, diluted to 63.5 percent alchohol (from about 70 percent) and placed into casks for maturation into whisky. The foreshots and feints go back into the low-wines still.

The casks in which the spirit ages are vitally important, since it’s estimated up to 80 percent of the flavor of whisky comes from the cask. (Some also comes from the water it’s made with and some from the fermentation—some distilleries use extra-long fermentation to enhance desirable flavors provided by the yeast.) Some casks were previously used to mature fine sherry. Others formerly contained bourbon. Hemicellulose in the oak gives the spirit sweetness and color. Lignin adds a vanilla flavor. Tannins make the whisky more fragrant. Bourbon casks are charred to release the flavor of lignin and remove undesirable flavors left over from the bourbon. The insides of sherry casks are toasted.

Aging must continue for three years for the spirit to be called whisky, and may continue for anywhere from five to 25 years—or longer. About two percent of the whisky in each cask evaporates each year through the porous wood. The unavoidable loss of this “angel’s share is one reason aged Scotch is more expensive.

Finally, of course, the whisky is diluted to the appropriate level of alcohol, then bottled. And how should it then be drunk?

George Yeo says the best way to appreciate whisky by adding a little water to it, up to about half and half, “or until the nose prickle effect of the alcohol disappears.” This helps the volatile aromatic compounds evaporate more easily. As well, at 40 percent alcohol, neat whisky actually anesthetizes the taste buds.

You might say water helps whiskey put, if not its first, at least its best, foot forward.