Tasting Whiskey

by Lew Bryson

  Peat is cut in turves, or strips, that are stacked and left to dry for a couple of weeks, then collected and burned in a distillery’s kiln to produce peated malt.

  If peating is on the program, it’s the first thing that happens in the kiln, because it works only on wet malt. The kiln will be stoked with smoldering peat, and the smoke will pass through the kiln for up to 18 hours. The smoke is not particularly hot; you can comfortably stand in the kiln during this stage. It’s humid, but it’s not even that smoky, because the malt’s absorbing it.

  The amount of smoke the malt absorbs is measured in parts per million (ppm) of phenols, the aromatic compounds that give the smoky aroma. They can range up to 60 or 70 ppm in the heavily peated malts. You may hear people talking about phenol numbers in the whiskeys themselves, but those numbers are not exact. The phenols in malt versus the phenols in the actual spirit run on about a 3:1 ratio, as a lot of the smokiness is left behind in the mashing process, locked in the husks of the malt. There are other variables in how smoky a whiskey is, with one of the biggest being how it is distilled. The best measure of smokiness is still the human nose!

  After peating is done, the heat is turned up; of course, that’s an immediate step if the malt is not to be peated. After about two days, the malt is dried. The whole malting process takes about a week, one maltster told me: grain goes in, malt comes out, and there’s not a lot you can really do to speed it up.

  That’s malt, the basis for single malt Scotch whisky and Japanese malt whisky. Irish whiskey is made with malt; the whiskeys from the Irish Distillers company (e.g., Jameson, Powers, Redbreast, Midleton) also contain a varying amount of unmalted barley. Although American whiskeys like bourbon and rye use a portion of malt for their enzymes, their main grains are different. Bourbon revolves around corn, and rye is centered on its namesake, but both use some of the other. Let’s have a look.

  What Is Peat?

  Peat isn’t hard to describe, but it’s somewhat hard to understand. It is partially decayed vegetation, mostly sphagnum moss, that builds up over centuries, or even millennia, in bogs, swamps, and moors. Why doesn’t the stuff just rot away? It’s covered in water.

  If you’ve ever gardened, you may have used peat moss to give sandy soil better water retention or simply to hold water around plants. That’s how peat accumulates. As the moss dies the new moss holds water in place, slowing the rate of oxygen transfer to the dead moss, so it doesn’t rot. A peat bog holds just enough water to keep that process slowed.

  As the decayed matter accumulates, it weighs more and more and exerts enough downward force (from gravity) that the bottom layers are compressed into a denser layer, something like particleboard. The peat is cut from the bog in long pieces, called turfs or turves, and laid out in rows or stacks to dry. You can see those drying turves along the road on Islay, cut by townspeople as free fuel for their fireplaces.

  A distillery that wants that smoky peat essence in its whisky will burn the peat in its kiln during the malt drying process. It’s a controlled slow burn; you don’t want very much open flame, because that’s burning too clean. What you want is voluminous, pungent smoke to rise through the green malt and bind itself to the husks.

  The interesting thing about peat for the whisky maker is that every place’s peat is different. Peat is found all over the world, from the tropics of Indonesia to the cold, high latitudes of such places as Tierra del Fuego, the Falkland Islands, Canada, northern North America, Finland, Russia, and Scotland. It’s estimated that 2 percent of the world’s land surface is peat bogs, so we won’t run out too soon. (There are already plans in place to conserve Scottish peat. Distillers are doing their part by investigating new techniques to get the most out of every curl of smoke.)

  The plants that grow in these bogs give each particular peat its character. Irish peat is different from Islay peat; Islay peat is different from Highland peat; Highland peat is different from Orkney peat. To a chemist it’s a simple matter of analysis. To a whisky drinker, it’s a matter of nosing; you can often smell the difference.

  Peat is a strong aroma/flavor, but if you’ve been to a peat bog that’s being cut for burning, or you’ve smelled unburned peat, you’ll know that’s not the smell in whisky. You might be told that some whiskies have a light peat character from using water that passes through peat on its way to the distillery; don’t believe it. Eddie McAffer, manager at the Bowmore distillery: “Just a romantic notion.” The only way to get that distinctive smell from peat is to burn it.

  For Scotch whisky that uses peated malt, the peat itself is an ingredient as surely as the malt or water. It’s part of the location, the terroir that makes whiskies different. I’ve been at the cutting face of Hobbister Moor, Highland Park’s peat source on Orkney. Standing on the clay sublayer that’s at the bottom of the moor, there was about 6 vertical feet of peat, representing about 5,000 years of accumulation. The top layer was loose, light brown, and full of heather stems and leaves and blades of rank grass. Farther down, the peat was more compacted, though still friable, and you could still see stems and leaves.

  All the way down, dating 5,000 years back, it was quite black and much harder . . . and I still saw some stems of plants that grew in that bog 3,000 years before the birth of Christ, 3,800 years before the Vikings arrived on Orkney. By now that peat, those stems, has probably been burned to flavor the malt of a batch of spirit for Highland Park, and in 15 or 18 years . . . Sláinte!

  Rye

  Rye is not a particularly well-behaved grain, which is not so surprising: it’s young, one of the most recently domesticated grains. Archaeological evidence for rye only goes back to about 500 bce, making it a relative adolescent among grains — and it acts like it.

  Rye grows exceptionally tall for a grass, 6 feet or more, and it often grows where it is not wanted. Its so-called volunteer stalks will pop up postharvest, and the grain is exceptionally quick starting. When it crops up in a wheat field, it damages the value of the harvest. It is also noted for its bitter, earthy taste, which was despised by the Romans, or at least by Pliny the Elder.

  Pliny found almost nothing good to say about the poor grass. In his Natural History he describes it as “a very inferior grain . . . only employed to avert positive famine.” He didn’t like how it tasted either: “Spelt is mixed with this grain to modify its bitterness and even then it is very disagreeable to the stomach.”

  But even Pliny had to admit rye’s good side: “It will grow upon any soil, and yields a hundred-fold; it is employed also as a manure for enriching the land.” Farmers say rye will grow on rock, and indeed, on a rye farm I visited in Alberta, there were shoots of rye springing up anywhere there was the barest amount of soil or dead grass: on rock, on buildings, on farm machinery.

  Rye is so tenacious, quick growing, and heavily rooted that it needs no weeding; it simply chokes out anything that tries to compete with it. It holds the soil against erosion, and as Pliny notes, it can be grown on a 2-year cycle, plowed back into the soil for fertilizer the first year. Those are the qualities that made rye popular in eastern Europe and Scandinavia, where pumpernickel and rugbrød are staple breads.

  Of course, if it makes bread, it will make whiskey, and rye can be readily malted. The Germans knew that as well as anyone. When they emigrated to North America in the 1700s, they brought rye and a knowledge of distillation with them. Pennsylvania was soon dotted with farm distilleries, and the flavorsome rye whiskey they made became an American classic. Canadians learned about rye the same way, and the tall, unruly grass took well to the uneven soils of the East and the broad sweep of the prairie.

  Whiskey Grains

  Malt Whisky

  (Scotch, Japanese, some Irish)

  100% barley malt

  Grain Whisky

  (Scotch, Japanese, some Irish)

  Varying grains; often wheat

  Single pot still Irish whiskey

  A mix of malt and raw barley

  Rye whiskey

&nb
sp; 51+% rye, plus malt and corn

  Canadian whisky

  Corn, rye, and malt; actual ratios vary widely

  Bourbon

  51+% corn, plus malt and either rye or wheat

  Corn

  The other big American distilling grain is corn. It may seem hard to believe that corn is a grass, particularly when you’re looking at a span of trimmed lawn next to a cornfield, but both plants are true grasses, members of the family Poaceae. Wheat, rye, and barley are clearly grasses — just bigger — but corn has a much thicker stalk, and the kernels, the grains themselves, grow on a fairly large cob, wrapped in a protective husk. It’s a strange-looking grass.

  Grass it is, though, and that’s why it works so well for distilling. Corn is king in North America, and it’s been bred to be so. Maize, as it’s called in much of the rest of the world, descends from a grass called teosinte, a wavy frond-like plant. Native Americans successfully crossbred teosinte until it was a single stalk, bearing increasingly large and grain-covered cobs. The increase in yield is nothing short of astounding, and corn has become a crop so important to American food technology that it shapes it in ways most of us can’t conceive.

  But for our purposes it’s easy to see why American distillers chose to use it: its incredible fecundity. Given good soil and the right climate — and corn has been bred to expand that range quite a bit — corn will put forth a huge amount of grain. It is difficult to malt, but there’s more than one way to husk an ear; once corn has been milled and cooked to split open the starchy matrix, a relatively small addition of malt provides the enzymes to convert corn’s plentiful starches to sugars in the mash.

  Corn’s only problem is that it’s a bit of a one-note song; the flavor is sweet and strong. So farm distillers learned to create a recipe, what we now call a mashbill, with a lot of corn for the sweet flavor and fermentation-fueling sugar, a portion of malt for the enzyme power to convert the starches to sugars, and a couple of sacks of rye (or sometimes wheat) to spice things up and put some flavor into the liquor. They had the grains milled (probably leaving either a portion of the meal as payment — millers were often distillers as well — or a promise of the whiskey to come), and then it was time to mash.

  Cooking the Mash

  Whatever kind of grains you’re using, whether malted or smoked, or not, they’ll undergo mostly the same process now. The grains are milled to the consistency of flour to make a grist, which is then mixed with water.

  The water matters — quite a bit — and distillers are usually located near good sources of water. To begin, distilling requires plentiful water for cooling; the alcohol vapors need to be cooled and condensed as they come off the still, and fermentation needs to be cooled in the summer so the yeast doesn’t run riot and ruin the mash. But cooling water can be from almost any clean source. The actual distilling water is more important. Calcium in the water supplies needed nutrients to the yeast; iron in the water will ruin whiskey, making it turn black and foul. The limestone layers under much of central Kentucky provide iron-free, calcium-rich water that is so good for whiskey making that I’ve heard distillers say that historic distilleries failed because they were “off the slab.”

  You need good water, then, and the proper consistency of grist going into the mash tun, the vessel where the starches in the grist, now called the mash, are converted to sugars. Depending on the distillery, the mash is either set at the appropriate temperature for this conversion or the mash is gently heated in rising “steps” to get different sets of enzymes to work at their most efficient levels.

  The temperature is crucial: too low, and conversion doesn’t happen; too high, and the enzymes will break down and nothing will happen. When the conversion does happen, it’s almost mystic. The starchy mash is thick and heavy, like oatmeal. Then the enzymes work their magic, and suddenly the mash is slippery and slick with sugars, a stunningly evident physical transformation.

  At this point there is a divergence in practice. In most distilleries the sugary liquid (called “worts”) is strained out of the mash, and the sugars left behind will then be washed out of the mash with successive applications of hot water, called “sparges” or simply “waters.” That hot water also brings a final conversion with some more complex sugars. The complete run of worts and sparge waters (except the last sparge, which usually becomes the grist water for the next batch) is then cooled in a heat exchanger and sent to fermentation. Traditional American distillers don’t strain the mash; the whole thing goes to the fermenters, floury grain bits and all.

  Sour Mash

  Ask whiskey drinkers what “sour mash” means, and they might tell you, “It’s Jack Daniel’s, that’s the real sour mash whiskey; it’s got that sour mash tang.” Really? The sour is just in the mash. By the time it gets through the still, the sour’s gone, and as anyone can tell you, Tennessee whiskey (and bourbon, its kissing cousin) is sweet.

  You may also hear that sour mash is like a sourdough starter, with the distiller holding over a small part of the already fermented mash, now sour, to the next fermentation, to ensure continuity between batches. Except that the sour mash — also called stillage or setback or, confusingly, backset — is what comes out of the column still, after a trip through live steam. There’s nothing alive in there. It’s a thin, sour liquid full of dead yeast — just what your mash needs.

  That “sour mash” is added to the fermenter with a new mash; as much as a third of the volume in the fermenter will be sour mash. The sour mash does two things: it feeds the yeast; the dead yeast is perfect food for the next generations of yeast, and there are leftover enzymes in there to boost the ones in the fresh mash. It also drops the pH of the mash, making it slightly acidic — just the way the yeast likes it — and headed for the sour state that will make the next batch of sour mash.

  Why does the yeast like acidic mash? According to Jeff Arnett, master distiller at the Jack Daniel Distillery, which rather famously uses sour mash, it doesn’t . . . not exactly. He compares yeast to a racehorse with a reputation as a “mudder,” a horse that performs well on a wet track. “A wet track does not make a mudder run faster,” Arnett noted, “but it can run faster on a wet track than the other horses.”

  Similarly, an acidic mash slows the yeast, but it slows the bacteria in the mash even more. Bacteria are a problem for distillers. They eat sugars, but they don’t make alcohol, and they usually produce off-flavors. Slowing them down allows the yeast to overpower and outreproduce them.

  So sour mash is about continuity and consistency, but not in the sense of a sourdough starter. It’s about making sure the distiller’s yeast strain is the dominant activity in the fermentation, and that every fermentation is a healthy and vigorous one, just like all the others.

  Sour mash is part of almost every bourbon made; there are a very few one-off bottlings that are made without it just as experiments. Almost everyone thinks he knows what it means . . . and now you really do.

  Fermentation

  The mash will fill about two-thirds of the fermenter. The remaining volume in the fermenter will be filled with sour mash, what’s left after previous fermentations have run through the still. The distiller’s particular strain of yeast is added and fermentation begins, converting the sugars in the mash to alcohol and carbon dioxide.

  Fermentation speed and temperature can have an effect on the aromas created by the yeast. Fermentation is a heat-producing (or exothermic) chemical reaction, so the wort will get warmer as it ferments (unless it is cooled by the distillery). Heat will make it run faster and create more aromatic compounds. Some of this can be desirable; too much is not. Which strain of yeast is used can also have an effect (see Four Roses’s five yeasts), which is why distillers are so careful to keep their yeasts clean and healthy. They’ll subject samples to microscopic analysis to make sure the strain isn’t mutating.

  The product of fermentation, at between 8 and 18 percent alcohol by volume (ABV), depending on the distillery and the yeast, is now
called “beer” by American distillers and “wash” by the Scottish and Irish. It’s ready for distillation.

  Pine “washbacks,” or fermenting vessels, at the Ardbeg Distillery on the Isle of Islay in Scotland

  Distillation

  The mechanics of distillation at the different distilleries can be a confusing subject, and it’s no wonder. There are pot stills, column or continuous stills, hybrid stills, and extractive distillation stills. They all work differently, but they also all work the same, by concentrating alcohol through separating it from the wash or beer, the initial product of fermentation. Most whiskey distillation relies on a series of two or more distillations, each one either bumping up the alcohol content or cleaning the spirit of unwanted impurities.

  Whisky stills at Glenfiddich’s distillery at Dufftown in Scotland; note the three different geometries.

  Batches of Pots

  Distillation on a pot still is a batch process; you put a “charge” of wash into the still, you heat it till it’s done, then you clean the still and start over.

  Pot stills are easy to understand; everyone’s seen a pot. To see how a pot still works, take a cooking pot, put water in it, and put it on the stove. Put the lid on it, and turn on the heat. As the water boils, the steam hits the lid, which is cooler than that hot metal below. The steam condenses; you can see it on the inside of the lid when you lift it off.

  That’s exactly how a pot still works, with two important differences. The first is the whole key to distillation: alcohol boils at a lower temperature than water. So heating the still and its contents to a point between the boiling point of alcohol (ethanol) — 173°F (78°C) — and the boiling point of water — 212°F (100°C) — will give you a long yield of vaporized alcohol that can be condensed and captured.