by Lew Bryson
How a Pot Still Works
That’s assuming you’ve provided for the second important difference between a pot and a pot still: an outlet. Stills need an exit for the alcohol vapors. When those vapors come out of a pot still, they go through a neck at the top, then into a sideways tube called the lyne arm. Lyne arms may bend down sharply, or gently, or more horizontally; some angle up. It’s all about reflux: redistillation within the distillation.
Reflux is something that doesn’t get talked about much by whiskey drinkers, but it can have a huge effect on the taste of the whiskey. Aficionados will tell you all about the water source, and the barrels, and the warehouses, and the peat, but it’s not often you’ll hear someone mention the amount of reflux.
It’s not that hard to understand. Reflux refers to the amount of vapor that condenses and falls back into the still before “escaping” to the condensers. The more that happens — that is, the more “reflux” there is — the more the spirit gets cleaned up before it is passed on to the next stage. Short, squat stills have less reflux than tall stills and will produce a heavier spirit; similarly, an upward-aimed lyne arm will drain condensing vapor back into the still, passing only the hottest, purest vapor and producing a lighter spirit.
Some of cleaning is through the evaporative process, a purification through boiling, but a lot of it is in the contact with the copper skin of the still, another thing that doesn’t get talked about much. Copper isn’t just pretty; it’s crucial to the distillation process.
Copper: The Guardian
Copper pot stills gleam in a distillery. Copper-walled column stills hiss and bubble away, sometimes with an extra load of copper scrap in the top. Copper abounds in a stillhouse. But it wears out and gets dented; it tarnishes and can look ratty. Why are distillers in love with copper?
“Originally copper was used because it was available,” Dr. Bill Lumsden explains. “It was malleable, you could shape it fairly easily into the shape of a still, and it had good heat transfer capability. That’s not so crucial nowadays, because most of the heating is done by steam coils inside the still, but in olden days it would be heated over a coal fire or something like that, so we needed to conduct the heat to whatever was inside. It was by chance that it was discovered that the copper chemically reacts with the condensing vapors.”
The copper combines with sulfur in the vapor — the sulfur comes from the grains; it’s a component of some proteins — to create copper sulfate. The sulfate, a black noxious-smelling compound, stays behind, leaving the spirit to flow clean.
At Woodford Reserve the runoff from the first still is caked with copper sulfate; here the copper reaction also is pulling out the oils from the corn in the mashbill. “The grunge,” says master distiller Chris Morris. “We call it the grunge. Don’t touch it, you’ll be washing the smell off your hands for three days.”
Take the copper out of distillation, and that’s what your whiskey would smell like. “It would be very pungently sulfury, meaty, almost a cabbagey smell,” says Lumsden. “Not really what you would want. Not only would there be too much of the sulfur itself, it would mask a lot of the fruitiness and subtlety of the whisky.”
Interestingly, the binding of copper to the sulfur takes away copper as well as sulfur. The stills, the condensers, the lyne arm: everything copper in the distilling path has to be replaced at some point as it gives itself up to make the whiskey tasty and aromatic. If the best examples of humanity have hearts of gold, surely the best whiskey has a gleaming heart of copper.
That’s why, according to Dr. Bill Lumsden, head of distilling and whisky creation for Glenmorangie and Ardbeg, the two different types of condensers used at Scotch whisky distilleries make such a difference in the spirit. Shell and tube condensers enclose up to 250 copper tubes in a copper shell that the vapor passes through from the lyne arm; cold water runs through the tubes and encourages condensation, and thus reflux. The other type of condenser is a simple worm tub, where the lyne arm feeds a copper worm, the familiar spiraled tube that runs down through a tub of cold water.
Lumsden used to work at a distillery where both types of condensers were used. “I could pick out the difference, nosing and tasting blind,” he recalls. “There was such a distinct difference. The whisky made in a distillery with worm tubs is typically much more meaty and sulfury in character.”
After the first distillation in the “wash still” has fully begun and the condensed, cleaned-up spirit starts to flow, there’s a decision to be made. Is this spirit good enough to become whiskey? This is where the makers earn their keep: the cut. When spirit first flows from the wash still, it’s not what they want. It is at a much lower proof, contains undesirable components, and has a character to it that will never become good whisky. This first part of the runoff from the still is called the “foreshots.” It will be diverted to a tank and added to the next run to be redistilled.
When the runoff reaches the proper high percentage of alcohol (there are many “alcohols”; the one whiskey makers are looking for is ethanol), the flow is directed to a holding tank; this is the “heart cut.” The heat is carefully adjusted to maintain the flow of heart cut for as long as possible, but eventually the time comes to divert the runoff again; this is the final part of the runoff, called the “feints.” The feints are also redistilled with the next wash run.
The heart cut — now called “low wines,” at around 20 percent ABV — will be distilled in a smaller spirit still, and again, the cuts will be made. This time the cuts have a much greater effect on the character of the spirit; the foreshots and feints remain behind (to be added to the next run). A tighter heart cut will give a cleaner, lighter spirit; a broader cut will yield a spirit with more of the various esters, aldehydes, and higher alcohols, known as congeners (see What You’re Tasting), giving it a deeper, somewhat oily character. The overall proof of this runoff will be much higher, closer to 70 percent. It is now ready to be put in barrels to age.
Columns: Ugly and Efficient
Column stills are everything pot stills are not. They’re ugly, just tall columns of bolted-together sections with screwed-down access plates, often tarnished or even rusty, and usually not included on tours. They’re quite similar to each other, varying mostly in scale rather than geometry. They’re loud, hissing and roaring with the rush of live steam. They run 24/7, not in batches — they’re also known as “continuous stills” — and there’s no heart cut to be made, just a steady stream of high-proof alcohol.
Not very exciting, right? It’s actually fascinating once you learn what’s going on in there, and how nineteenth-century distillers cracked the problem of efficient distillation. Pot stills produce good-quality spirit, but there is a necessary downtime between each distillation when the still is being emptied of waste, cleaned, refilled, and then heated for the next distillation. Distillers wanted a way to produce a lot more spirit, quickly, efficiently, and consistently.
The key to the column still is the idea of wash, or beer, moving in one direction — falling downward in the column — as live steam moves up through it in the opposite direction. The wash meets the steam, and as it moves downward the alcohol evaporates and moves upward with the steam; the steam (water) cools and falls downward, and the alcohol vapor becomes more concentrated as it reaches the cooler top of the column. As long as wash and steam are being fed into the column, distillation continues, and high-proof alcohol comes off the top in a steady stream. All a distiller has to do is keep up with fermentation and keep an eye on outputs.
It’s a bit more complicated than that. The wash doesn’t just fall through rising steam in an open column; it would fall too fast to be heated above alcohol’s boiling point. Instead, there are perforated plates in the column that hold the wash, spaced about 15 inches apart. Steam rises through the holes, stripping away the alcohol as it evaporates (some distillers call the column still a “stripper still”). As the weight of the wash overcomes the pressure of the steam, it moves downward to the next
plate, where the process happens again and again, the wash dropping down and the alcohol vapor rising, until all the alcohol is stripped out and the liquid waste drains out the bottom (that liquid waste is then cooled and used as sour mash in bourbon fermentation).
Bourbon distillation uses a single-column still and, you’ll recall, unfiltered beer, with the grain passing down through the still. The vapor is condensed, and the spirit, now at about 140 proof (though every distiller is different) and at this point called “low wines,” is sent to the doubler, essentially a classic copper pot still. Here the whiskey may be slightly raised in proof, cut to leave undesirable flavors behind, or simply run through to react with the copper; again, every distiller has different techniques. Regulations require that the distillate be no more than 160 proof after this final distillation step to make whiskey.
Grain whisky in Scotland is made with a slightly different setup. Scottish distillers use the classic two-column still as perfected by Aeneas Coffey — ironically, an Irish exciseman, or whiskey tax collector — in 1830. The Coffey still (as some distillers call it) has two columns, the analyzer and the rectifier. The wash is preheated and introduced into the top of the analyzer. This is like the single column of the bourbon still, and after the alcohol is stripped out through the plates, it passes to the bottom of the rectifier.
The rectifier is designed to pull off alcohol while allowing more volatile and undesirable congeners to rise to the top of the column. The alcohol stream vaporizes and moves upward through another series of plates, again concentrating as it moves up. Unlike a bourbon distillation, the idea here is to get a much cleaner, purer stream of alcohol, and for grain whiskey that usually means the spirit comes off the rectifier at above 90 percent alcohol, a whopping 180 proof. The flow from the bottom of the rectifier is recirculated into the wash to be sure all the alcohol is recovered; the higher volatiles from the top of the rectifier are either released to the atmosphere or used for chemical feedstock.
Confused? Don’t feel bad; it takes a while to figure out everything that’s going on in there. If it helps, think of the column still as a series of pot stills perched on top of each other, each one working a batch and sending the vapors up to the next one.
How a Double Column Still Works
1. Cool wash enters the rectifier column and flows through a system of piping, heating as it goes.
2. Hot wash flows out of the rectifier and is run to near the top of the analyzer column.
3. The hot wash flows into the analyzer column and down through a series of perforated plates. (Note: This is where cool fermented mash would enter the column for bourbon, rye, and Tennessee operations as a first step.)
4. As the wash trickles down, live steam moves up through the plates. The hot steam evaporates the alcohol, turning it into a vapor, and carries it along to the top of the column.
5. The leftovers — spent wash and mash solids — flow out of the bottom of the column. In the bourbon - making sour mash process, the watery mash solids — called “slops” or “stillage” — will be added to unfermented mash as “setback.”
6. Hot, impure alcohol vapor flows from the top of the analyzer column. Alcohol levels vary at this point, but they are well over 50%. For grain whisky, the vapor goes to the bottom of the rectifier column, as shown here; for bourbon, the vapor goes to a pot still–like doubler for further purifying.
7. Hot alcohol vapor enters the bottom of the rectifier column and rises through another series of perforated plates. As it rises, it comes into contact with the gradually cooler piping that holds the wash. Some impurities — and water — condense and are left behind (in most cases they drain to the bottom of the column and are pumped to the analyzer for further distillation).
8. Alcohol vapors hit the “spirit plate” and condense at this particular height and temperature. Higher alcohols and other more volatile impurities continue to rise (in most cases they are condensed and returned to the incoming wash feed for redistillation).
9. Hot alcohol flows to the condenser and spirit receiver at approximately 90 to 95% ABV.
There’s a third type of still that involves adding water to pull off more congeners, but I’m going to address that in the chapter on Canadian whisky (see here), since that’s where I saw this still in operation, and because Canadian distillers seem to be the ones most interested in the clean spirit that this extractive distillation can give them.
At the end of the distillation process, the results are roughly the same: a clear, high-proof spirit that’s ready to be entered into barrels for aging (or to be bottled as “white whiskey”). The spirits that are lower in proof have more flavor and aroma, but not all of it is desirable. The spirits that are higher in proof are cleaner and without undesirable character, but they have much less aroma and flavor. The barrel will help filter the former, add flavor to the latter, and give both color.
We started in a field of grain, then malted it, milled it, mashed it, fermented it, and distilled it. Malting took a week; mashing and fermenting took another 5 or 6 days, and distillation another day. Two weeks of constant activity will now lead to the filling room, where the spirit will go into a barrel, then into a warehouse . . . and then will sit there for years. We’ll talk about wood in the next chapter.
Hybrid Stills: When You Just Can’t Choose
The pot still makes for great single-batch control and allows a careful distiller to cut the spirit right where he wants it. The column still allows greater reflux, a clean spirit, and much greater efficiencies. Many craft distillers, faced with the choice, have opted to do both.
Modern still makers offer a hybrid still, with a column sitting atop a pot. The appeal is that the column is adjustable. If distillers want to run it as a pot still, they can open up the plates, and it’s . . . kind of like a pot still. If they want to run a bourbon-type spirit, they can close off some of the plates. If they want a cleaner spirit for vodka or for “white whiskey” (the unaged whiskey often sold by craft distillers) they can close up the plates and recirculate within the column, or even send it out to another column, using the pot mainly to heat the spirit. They can even put a bulbous “gin head” with no exit pipe on the still and recirculate spirit through botanicals, allowing it to fall back into the pot.
If you see one of these hybrids in a craft distillery, don’t be fooled if your tour guide tells you it’s a pot still. It’s not really a column still, and it’s not really a pot still either. It’s something else, quite flexible, and able to be changed up as the distiller wants.
Aging
Take the clear spirit we saw at the end of the previous chapter. That’s what our ancestors of 200 years ago would probably have recognized as whiskey. They may have mixed it with hot water and sugar and flavorings, or infused it over a period of days or weeks with herbs, bark, fruit, flowers, or other natural flavors, or they may have bolted it straight.
But 200 years ago whiskey was, for the most part, raw, or unaged. If it was aged, it was by accident, not intent. That was about to change, and whiskey would be transformed from a rough mental anesthetic to a world favorite with a distinct air of sophistication. The transformation would arise from a piece of ancient technology: the barrel.
Barrel Aging
Barrels had been a major advance for the ancient world long before whiskey came along. The practice of steaming wood in order to bend it is believed to have been first developed for boat building. Some bright person, most likely a Celt, borrowed the technique to bend and piece together wooden staves into a cylindrical shape that curved inward at top and bottom and was capped at each end with a lid, or head, fitted into a groove in the staves. The earliest barrels were held together with rope; eventually the rope was replaced by metal hoops that were riveted together and hammered onto the bulge of the barrel.
Scotch whisky maturing in oak casks in a classic earthen-floored “dunnage” warehouse
The barrel was actually quite ingenious and much more than a simple container. It wa
s a way that one person could control a heavy load, well past his or her ability to lift or hold. Every year at the Kentucky Bourbon Festival, you can watch the Bourbon Barrel Relay, where bourbon warehouse workers roll barrels (filled with water, not whiskey, for the event) down a set of tracks and into a simulated warehouse rick, the set of wooden rails that hold the barrels. They roll the barrels as fast as they can, make right-angle turns, and can rock the barrels up on end to make them turn or bring them to a stop. The barrel’s round shape and curved sides allow one person to quickly and precisely control a little over 500 pounds of bourbon, while the uniform size makes it possible, with experience, to roll a barrel down the rails of the rick in such a way that the bung stave — the one with the hole in it, where the barrel is filled and then plugged with a poplar plug, called the bung — ends up topmost, where it can’t leak.
Early whiskey makers turned to barrels because they were better containers than earthenware jugs or leather skins for holding the liquid. Like the copper still, though, the barrel was capable of making the whiskey better in ways that hadn’t even been thought of.
Parts of a Barrel
Charring
One of the keys to maturing whiskey is charring the inside of the barrel by placing the open-ended barrel over a burner and blowing a hot flame into it. This controlled burn creates physical changes that transform the oak barrel from a mere container to a chemical reaction chamber, a filter, and an infusion vessel.