Archive for Distillation

Cooking with Gas

I see that Bruichladdich is finally starting to benefit from their pioneering biogas project. I covered this about a year ago, when I was much more active on this blog. They essentially take the waste vegetable matter from the malting and distillation processes and use anaerobic digestion equipment to generate gases (like Methane, presumably) that they can use to generate electricity. Since this is a very green project, I bet they aren’t using a boiler-type system to convert the gas to electricity; I suspect a fuel cell.

BTW, Bruichladdich is using the Lomond still I mentioned in that story to make gin: Islay gin. I’d like to try some of that…. I really love their “because we can” attitude — are we positive that Bruichladdich isn’t based in Silicon Valley?


The Basics of Distillation; Part 3

You’ll probably hear some unfamiliar terms in discussing the actual process of distillation. These terms appear in distilling brandy and whisky; I don’t know about white spirits like Vodka and Gin. One term is: Low wines. What does wine have to do with whisky? My theory is that this term probably came from some of the first applications of [double] distillation: Making brandy, which is distilled wine. So what’s low about it? Well, I suspect that the “low” comes from the fact that the ABV isn’t high enough yet, meaning the low wines have to be further distilled.

What about these: Foreshots? Heads? Middle cut? Feints? Tails? A “cut” is when the output of a pot still changes from undesirable to desirable (or vice versa). When the cut is made, the liquid output from the still is literally redirected to a different receiver (container). “Heads” (also known as “foreshots”) precede the “middle cut,” which precedes the “tails” (also known as “feints”). The “heads” or “foreshots” can contain unsafe or unpalatable chemicals. The “middle cut” is the desired output of the pot still. The “tails” or “feints” are what comes out of the still after sufficient alcohol has been extracted from the still such that the concentration in the output is no longer high enough.

We already know that the distillation process for Scotch takes at least two passes. The first pass is performed by the wash still, which takes the beery contents of the washback and concentrates the alcohol content to create the “low wines,” the output of the first step of distillation. The low wines are the middle cut of the wash still. According to this description, the foreshots off the wash still are discarded into animal feed. I have heard that a stillman (the person who operates the still; sorry for the politically incorrect term!) can tell by smell when the “middle cut” begins. The resulting low wines are 15-20% ABV, about double the alcohol concentration of the wash. Here are two additional descriptions of the distillation process, with decent diagrams.

It’s useful to step back and remember what’s happening here. The big picture is that distillation is a process of taking a liquid mixture that contains lots of chemicals with different boiling points, boiling the lot of them, and controlling the condensation process. The more volatile liquids will boil sooner than the less volatile liquids, so they can be preferentially captured since they will condense sooner. The pot still is not a continuous process. It is filled (the official term is: charged), and heated until virtually empty, then charged again for the next batch. (There are other types of stills that operate continuously, but they are not used in the production of Single-Malt Scotch Whisky. You’ll find them in petroleum distillation, Single-Grain Scotch Whisky distillation, and many other chemical engineering applications.)

The second step in the distillation process is another pot still known as the spirit still. The spirit still’s foreshots may be recycled into the wash still for the next pass. For most Scotch whisky, the middle cut is the final output: New make spirit. As with any pot still, the feints are too weak and are captured and recycled into earlier stages of the process. After the second distillation, the ABV is 65-70%, which strongly depends on the alcohol content of the low wines, which in turn strongly depended on the alcohol concentration of the wash.

Lowland Scotch Whisky and Irish Whiskey is distilled a third time, through a second spirit safe. The resulting new make spirit might be around 80% ABV. Since the spirit used to charge the second spirit still is already fairly concentrated in terms of ABV, this additional step doesn’t increase the ABV as much as the pass through the first spirit still did. Occasionally, Single-Malt Scotch Whisky is distilled a fourth time. Bruichladdich recently did this with their “X4 (Perilous Whisky).” The final ABV of that product was 90%…you can see that each step is giving diminishing returns in terms of ABV. On the other hand, there was enough Ethanol in this product to run a Formula 1 racing car.

Aside on ABV: A higher ABV has an interesting effect. Because alcohol’s boiling point is less than human body temperature, when a high-ABV whisky hits the tongue the alcohol “flashes” — it evaporates very quickly. This carries aromas to the nose that may not be obvious before you taste. Keep in mind that the ABV of the final bottled product is less than the ABV of the new make spirit that goes into the spirit safe because the aging process reduces the ABV by up to 3% per year in Scotland, depending on seasonal humidity and temperature variations.

The Basics of Distillation; Part 2

There are two key components to the pot still. The part where the liquids and solids are (the beery wort created by the yeast) and the vapors that come off of it. Remember, the contents of the still include proteins, amino acids, enzymes, carbohydrates of varying complexity, phenols, alcohols, dead yeast, acids, and other chemicals, not all of which are water-soluble to the same degree (if at all), and some of which are alcohol-soluble. It’s not a simple Ethanol+Water mixture. The goal of distillation is to separate the good stuff from the bad, in a way that is very repeatable. If you make whisky, you need to do this in such a way that each batch of each of your expressions tastes the same from one batch to the next.

It’s been said that Scotch whisky has been said to have over 800 unique chemical compounds within it that contribute to the flavor. Distillation is the process whereby those chemicals are delivered from the wort to the cask. The point of distillation is to produce a liquid with progressively less water (by volume) and progressively higher alcohol (by volume). The point of distillation of Scotch is not to produce pure Ethanol (grain neutral spirits). Pure Ethanol would taste like Vodka…perhaps even blander than that. Scotch producers (and whisk(e)y producers in general) want to preserve the impurities that give their product its unique tastes and smells.

Modern pot stills use integral steam pipes that indirectly heat the wort from within. A still can hold thousands of liters. The temperature is presumably kept below the boiling point of water, but I don’t know that for a fact. Traditionally, direct heat was applied to the bottom of the pot still, and regardless of the source, the heat causes the alcohol and other vapors to escape into the conical or cylindrical column above the liquid level.

As the liquid is heated, the vapors interact with the copper interior of the still, which is said to influence the flavor (no one is precisely sure what’s going on there). Some of the vapor condenses and interacts with the copper multiple times before the condensate is taken out of the still. Stills have various shapes and the surface area and angles are different, which again is said to produce different flavor profiles in the new make spirit.

At the top, there is a downward-angled tube that carries the condensate to the next step of the process (either the next still, or ultimately the spirit safe). The tube is called the Lyne Arm, and is depicted in this excellent diagram. That carries the vapor with its alcohols and aromatic compounds (some of which is presumably already condensed) to the condenser, where most of the condensate is produced. This article on stills lays out many different designs but uses no definitive language: What seems to be clear is that different shaped stills produce different qualities in the spirits, but it’s also true that the stills are not all using the same input. The scientist in me wonders if anyone has tried using an identical mash formulation into various shaped pot stills to see what the specific chemical difference is due to shape alone. Also I wonder what kind of product would emerge if copper were replaced by stainless steel, or glass, or any other chemically inert material.

Next, in part 3, I’ll get to the final specifics of the process: What is the point of multiple distillations? What happens in the first? The second? The third?

The Basics of Distillation

Well, this has been much delayed, but I wanted to write down what makes distillation possible. It’s really not a complicated idea. The first part is what I already wrote about: You create a solution (somehow) that has a mixture of liquids with the idea that you want to separate them. Not all liquids are mutually soluble, but since water is known as the “universal solvent,” most things (solids and liquids) can be dissolved in water. Therefore a common task that needs to be done is to separate water from the stuff that is mixed with it.

Evaporation is the key to distillation. Moreover, another important point is that not all liquids have the same boiling point. Oh, and the fact that boiling is a reversible process. Let’s step back: You don’t have to boil a liquid for it to evaporate. A pot of water, left alone, will turn into an empty pot (if you are patient enough). If you enclosed that water in a vessel of some kind and applied heat to it, you’d be encouraging it to evaporate at a faster rate, up to and including boiling it. But remember, boiling is reversible. When the water vapor gets far enough from the heat, it will turn back into a liquid (i.e., it will condense).

If our imaginary vessel is big enough such that the water vapor can get away from the heat, it will condense on the sides and slide back down to the [still boiling] water. This brings up an important point: Such a vessel can’t be closed, can it? For most liquids, the space consumed by a vapor is MUCH larger than that consumed by the equivalent liquid. Thus a closed vessel would be under enormous pressure…probably dangerous levels of pressure. So the vessel will need to be open. Now, can we make the fact that a vapor wants to condense back to a liquid as it cools off work for us?

If the imaginary vessel has a level somewhat above the boiling water that is intentionally kept at a temperature less of 100 °C, the water will condense at that level. The act of changing phase back to a liquid will give off energy that will warm up the level, so it will take work to keep that level cool enough. I hated Thermodynamics in college, so I won’t even try to figure out how much energy this would take. Intuitively, it will take energy to keep that level at or below 100 °C.

When water is distilled (to purify it), the idea is that water vapor can be collected and condensed into “purer” water, leaving behind the impurities that might have been dissolved solids, and perhaps other liquids. Any liquids that boil at a lower point than water will be in the mix as well, unless great care is take to make them condense at a lower level, so the vapors that reach the water collection level are mostly water.

Separating liquids is easier when they have significantly different boiling points. For instance, Ethanol (78.4 °C) and water (100 °C). It’s not a perfect matter of just “boil the solution and catch everything that condenses at the desired boiling/condensing point temperature” because the vapor is a mixture of gases and the condensate won’t be a perfectly pure, isolated liquid.

Think about it: Even without applying heat, some of the water is vaporizing (evaporating) anyway. A glass of Scotch will have Ethanol wafting away even when you are not trying to boil it (don’t boil Scotch in my presence, please). Trust me on this, even though you can’t smell it, water is wafting away as well. And those other smells? The volatile compounds that make up the pleasing aromas and flavors? You can smell them because they are leaving the glass. When a Chemist says “volatile” they are referring to a tendency to evaporate. Common usage seems to equate volatility with inflammability, but that’s a different adjective entirely: Inflammable.

The trick with distillation, since it’s hard to get what you want after only one pass through the still, is to take the result and distill it further. After one pass, the distillate is not perfect, it’s perfected: It’s closer to where you want to be than whatever you started with. That’s what is done in the production of whisk(e)y.

Scotch is typically distilled twice, but some are triple distilled (makes the initial new make spirit higher ABV, compared to a double-distilled product, but the initial ABV and the bottle strength have no relationship with each other due to aging, mixing with water, etc.). As an aside, most Irish whisky (I’m particularly fond of Bushmills 16) is triple-distilled.

Bruichladdich has created a quadruple-distilled monster called “X4” that is nicknamed “Perilous Whisky.” When it went into the casks it was over 90% ABV. As a publicity stunt, they used X4 as fuel in a racing car. Seriously. Aside: I object to the plan to mix it down and sell it at 50% ABV. It’s closer to single-malt vodka. Come on…Glenfarclas makes a 60% ABV cask-strength expression. At least go for 66% ABV.

Now that some of the more mundane aspects of distilling are behind us, I’ll take a look at how a pot still actually works.

Diageo Malting Plant: Silo Collapse

I was sad to learn that the Port Ellen malting facility on Islay was damaged yesterday. Luckily no one was hurt, but hundreds of tons of barley was in the silo when it collapsed.

Grain elevators in the US mid-west frequently explode because of airborne dust which is highly flammable, even explosive. Presumably we’ll know in a few weeks what the cause of this silo collapse was; it could have been explosive dust, or perhaps a structural failure.

What’s a malting plant? Malting is one part of the whisky production process that is centralizable. Malting is the process whereby the barley is sprouted by wetting it and letting it sit, historically it was spread out on a large malting floor, for several days. The need for a large floor was why malting benefited from economies of scale, however modern malting has improved upon the floor malting which can be adversely affected by weather (variations in humidity, primarily). Malting is still, for the most part, centralized even though floor malting has pretty much disappeared.

Malting is how the whisky producers crack open the barley to expose the sugars to the yeast that will be used in the next phase of production. If the barley seed were sprouting in a farmer’s field, the carbohydrates inside the barley seed would be used by the nascent plant to provide energy for its initial growth. Whisky producers need those carbohydrates (sugars), so the plant can’t be allowed to grow beyond its initial sprouting. The sprouting process exposes the tightly locked complex carbohydrates and enzymes. To stop the growth process before it goes too far, the barley is heated and dried which stops the growth and preserves the sugar for the yeast.

The malting process involves both sprouting (germinating), then drying the barley. The drying is facilitated by heat produced by burning coal and/or peat, which may impart desirable flavors to the malt. Once the malted barley has been produced, it can be shipped to a distillery for the next phase of the production process, wherein the malted barley is ground and mixed with hot water, which facilitates the action of the enzymes which convert the complex carbohydrates in the powdered malt into simpler sugars that are palatable to yeast. If you are familiar with the production of beer, you’ll recognize much of this process. Once the yeast is added, it produces, over the course of several days, a weakly alcoholic solution at about 6-7% ABV (as the alcohol concentration is increased, the alcohol kills the yeast, which puts an upper bound on the amount of alcohol that the yeast can produce). The next step, distillation, concentrates the alcohol.

How does distillation work? It’s not magic. Alcohol is more “volatile” than water. This is a term that has specific meaning for chemists, and it basically means that alcohol boils at a lower temperature than water. If you have a liquid that contains some alcohol and some water, and if you heat it in a precisely shaped container (e.g., a pot still), the alcohol vapor can be induced to condense back into liquid form.

If the condensation process were allowed to reach equilibrium, e.g., in a vertical tube, the alcohol would condense on the walls of the cylinder (if it were tall enough) and drain back down to the bottom, from where it would be heated enough to evaporate again. The reason it condenses is that the tube is cooler as one moves farther away from the heat. No matter how tall the vertical tube is, some alcohol vapor will escape over the top. My sense is that this is why the pot still is bent at the top, so the whisky producer can contain the alcohol and control the rate and amount of condensation within the still.

Also, keep in mind that the vapor that goes up the tube is a combination of water vapor and other volatile chemicals that boil at less than the boiling point of water. Even if the liquid is only kept at the boiling point of alcohol, there will still be water vapor present in the atmosphere above the liquid, since water evaporates even when the liquid is less than 100 °C.

Per wikipedia: “The boiling point of the alcohol ethanol is 78.29 °C, compared to 69 °C for the hydrocarbon Hexane (a common constituent of gasoline), and 34.6 °C for Diethyl ether.” The initial condensate, then, will contain lots of other volatile chemicals that may have foul odors or tastes (these odors and tastes come from fusel oils and other chemicals associated with alcohol production that may remind one of paint thinner, acetone, etc. — you wouldn’t want to drink them!). The tough part at this phase of production is that the foul odors and tastes will be soluble in water or alcohol, so they may be difficult to separate from the more desirable esters and phenolic compounds that whisky producers may want to retain in the finished product.

Once the pot still (actually, a pair of stills) has effectively burned off the more volatile components, the refined alcohol is allowed to freely flow to the “spirit safe” where the amount produced is measured very carefully for tax purposes. The operation of the still involves the careful attention of the stillman who determines when the proper product is ready to be collected, and who knows when to cut off the production before the still runs dry.

The spirit is usually distilled at least one more time before going into oak barrels for aging. Bruichladdich has produced “X4” that is quadruple-distilled and due to the concentration being increased at each stage of distillation, the ABV of the final product was well over 90%. Some Scotch is triple-distilled, as is most Irish whisky. The initial alcohol concentration of the spirit that goes into the oak barrels is about 70% ABV. Then the aging process reduces that concentration as the alcohol gradually escapes the semi-permeable membrane that is the wood while the wood works its magic of imparting its flavors to the liquid. As long as the alcohol concentration remains above 40% ABV, the liquid in the casks can be bottled and sold as Scotch whisky, provided it’s also at least 3 years old and meets a slew of other technical requirements.

Now that I have written some basics about distillation, I will go into some more detail about types of distillation and explain in a bit more detail why distillation works at all.

A Fungus Among Us

Yeast is what makes essentially all alcohol. Beer, wine, whisky, vodka/gin, sake, tequila, etc., all get their kick courtesy of the humble yeast: A single-celled organism that is classified as a fungus. Seriously! The edible (well, drinkable) kind of alcohol is Ethanol (C2H6O). If you are a chemistry or biology geek, you will recognize that Ethanol plus water (in the correct ratio) can be converted into sugar through some cellular magic that combines some water with some Ethanol and yields Glucose (chemically: C6H12O6). The latter can then be readily converted to energy in the body, which is why alcohol has calories.

Yes, Ethanol is readily converted into sugar (Glucose), but the body loses water in the process, which happens in the liver. The water the liver needs to metabolize alcohol is pulled from the bloodstream, which is why hangovers are often associated with a dry mouth. One way to prevent this is to drink lots of water before bed. Aspirin also is rumored to work. The fact that the liver is the first stage in alcohol metabolism is why the liver is affected (adversely) by excessive, prolonged alcohol consumption. But never fear, alcohol (Ethanol) is produced naturally in the body and one of the liver’s many functions is to be able to metabolize alcohol, a need that far pre-dated the discovery of fermentation and distillation!

All of this because a lowly fungus is adept at converting sugar or other simple carbohydrates into Ethanol. I can’t find any examples of Ethanol being produced naturally, except via the action of yeast. And that’s the source of all the alcohol that most people (and many animals) love to consume. All the various forms of alcohol, be they beer, wine, distilled spirits, involve Ethanol production in which yeast acts on a solution of carbohydrates, typically simpler ones.

In the case of whisky, the barley contains the complex carbohydrates that would normally fuel its growth into a barley plant, but they are stored deep inside the seed and distillers must trick the barley into exposing them and the enzymes that can break them down into simple sugars. That’s key to the malting process. Another word for this is sprouting, except that normally when a barley seed sprouts it isn’t killed right away with heat from a peat fire. In malting, you need to stop the process at the right time so the plant doesn’t consume too much of the precious carbohydrates. That’s the drying, sometimes over peat, sometimes over coal. Then the dried malted barley is mashed, warm water is added, and eventually yeast is added once the enzymes from the barley have been induced to break down the complex carbohydrates into simple sugars that are palatable to yeast. This action of the yeast on the mash makes a beer-like wort that is allowed to come to about 6-8% ABV over the course of several days. Then this is distilled, which concentrates the alcohol. Multiple distillations may be used to achieve higher concentration of Ethanol per unit volume. Scotch is, IIRC, usually distilled twice and put into barrels at about 70% ABV. Over time, the alcohol escapes and the barrel strength is reduced to no less than the legal minimum of 40% ABV. To be called Scotch, the final product has to be at least 40% ABV.

Sorry for the rambling post, but I thought it would be fun to give credit to the lowly yeast, without which this blog would not exist!