The outcome of the Poll was an overwhelming “Yes”. So here we go: another more technical post. This time on column design. I foresee three articles. This first one will lay the groundwork on how a column should perform. The second one will analyse the workings of the bubble cap column, since that’s the one most often used by Craft Distillers. The third post will zoom in on how we translated our design philosophy into creating the iStill 250 and iStill One family.
In this post, on how to design a good column, we focus on whiskey making. More posts will follow, that will deal with other drinks.
Why start with whiskey? Well, because … there’s quite the gap between many of the designs used right now for whiskey making and how a whiskey column should be designed optimally. A nice starting point, therefore!
It is adviced to read both posts on Boiler Design prior to starting to read this one. A good design starts with the boiler. And the groundwork of how I feel about total still design is layed out in those two posts. Well designed columns, litteraly as well as in a figurative way of speaking … have a great boiler at their base.
What are we after?
It is easy to say that this or that design is better. But how to measure? What is the goal? Luckily, in whiskey making, that’s quite easy. As it is the case with all taste rich drinks … when distilling a whiskey, we are after taste. So a column should be designed in a way that allows for maximum taste transfer. Now, that’s a starting point, we can depart from.
Next question is … where can the taste of a whiskey be found? That’s a question that’s less easy to answer, but let’s dive in deeper and find out.
The tree metaphore
I find the “Tree Metaphore”, that I originally developed for gin recipes, helpful. You can envision a distillation run by looking at a tree, “outside – in”. That’s the trick.
The first thing you see and the first things that come over are the fruits AKA fruity notes. When you dive in deeper, you notice the leafs, AKA herbs (the metaphore was originally designed for gin, remember). The stem or trunk comes next, representing the body or Hearts. And you have to dig them up, and really go in … but there’s roots too. Rooty and nutty flavours are found in Tails, the last bit of the run.
Simplified, and translated to whiskey making, there’s fruity tastes in the Heads, body in the Hearts, and rooty and nutty tastes in Tails.
Now the next step … taste definition of whiskey … whiskey certainly has body, and some whiskies have some fruitiness, but the main character trait of whiskey is its rooty and nutty notes. That’s Tails associated.
In other words … it’s the (early) Tails that are most important, when you are in the persuit of making a great whiskey.
That’s where – after some ageing – the goodies, the character, the multi-dimensional after taste, that lingers and lingers in your mouth, can be found.
If early Tails have the most impact, when in the persuit of a great whiskey, the column of any whiskey distillery should facilitate harvesting those early Tails, right? But what are the properties and qualities of early Tails? It is only when we know these, that we can start to put together a framework of “do’s” and “don’ts”, when we want to design a great column for whiskey distillation.
Early Tails and the art of smearing
We want some Tails into the last parts of the Hearts run. That’s the goal, when making a great whiskey. This process is also called “smearing”, where – instead of pure and perfect cuts – there are Tails and Tails related congeners (taste molecules) “smearing” into the last part of the Hearts cut. The more Tails congeners you harvest during the run, the more taste potential your whiskey will gain. But reaching that full potential will evidently take longer ageing.
When do Tails come over? Yes, at the end of the run, that’s for sure. But how late? The later they come over … the more compacted they will be. Very well compacted Tails come over very late, so your Hearts cut will be quite big, but there won’t be any Tailsy congeners … until they come over. And then it is too late. Due to the compaction, they come over all at once. Like a big gulp, over-contaminating Hearts and making the final product undrinkable.
When making whiskey, great Tails compaction and control either don’t bring over taste or overpower it completely. Perfect Tails compaction just became enemy of state … Now, that’s a statement that can help out, when designing the perfect whiskey column!
Properties of Tails
When Tails management is essential to creating world class whiskey, the properties of Tails need to be further investigated. That sounds like a challenge, right? Chemistry and stuff …
Fortunately, it all boils (litterally!) down to … boiling points and weights. Wait, let’s turn that around: molecular weight and boiling points.
Simplified, Tails associated alcohols like Propanol, Buthanol, and Furfurral are “heavier” (= have more intermolucular bonding power) than the good alcohol called Ethanol. Because they are “heavier”, they don’t escape a boiling concoction (AKA your distiller beer) as easy as lighter alcohols or Ethanol. And when they do, most of them are so heavy that they fall back. Back into what? Back into the distillers beer you are currently distilling.
Since Tailsy alcohols are heavier, they do not come over until the last part of the run. And they only come over when enough energy is applied for them to make it to the column and beyond. Energy? Yes, energy. Energy that is translated to speed. Remember, Tailsy alcohols are big dudes with an overweight problem. You need to put a lot of energy in them to get them moving. And it takes a lot of speed to get such heavy molecules all the way over to the product condensor.
Speed? Did anyone just say “vapour speed”? I guess I just did …
Vapour speed is king
When it comes to Tails management, vapour speed is king. Low vapour speeds are great for Tails compaction, but there may simply not be enough speed to carry early Tails over into Hearts. High vapour speeds are what you need if you want to smear early Tails into Hearts.
How to increase vapour speed
We established that a great whiskey can only be made when we master the art of smearing early Tails into Hearts. Translated to column design, this means we need a column (or distillation system) that allows us to do that in a gentle, controlled manner.
There are two ways in which we can increase vapour speed:
- Increase power input;
- Decrease column diameter.
Increasing power input creates more gasses that travel through the column at a faster speed. A smaller diameter column does not create more gasses, but dramatically increases vapour speed.
A – relative – increase in power input can be created by designing efficient stills. The less energy is used to heat-up the distilling room, the more energy is left to play around with vapour speeds. The smearing of early Tails into Hearts can be facilitated by designing relatively small diameter columns. Small diameter columns in combination with efficient stills.
Hey, did you notice that? All of a sudden we have “do’s” and “don’ts”! Let’s approach it from the positive side … so what are the “do’s”? What do we need to do in order to create the best column for great whiskey making? The total rig needs to be efficient. And the column on which final cuts are made needs to be relatively narrow. Time for an example from practice.
How the Scots do it
The Scots, like no one else, make whiskies that have lots and lots of taste. So they must master the art of smearing early Tails into Hearts, right? How do they do it? Magic? Heritage? No, they do it by designing an effective still … with a narrow column. The stills the Scots use to help them smear early Tails into Hearts are quite efficient and have high vapour speed columns.
How they make the rig on which they want to smear early Tails into Hearts efficient? Easy, by doing a strip run first. The strip run augments total ABV from something like an 8% wash to a 25 to 30% low wines. And that’s what they charge their spirit stills with. Filling them with higher ABV charges dramatically increases the efficiency of their spirit run.
How they create high vapour speeds, that allow Tails to smear into Hearts, on the spirit run? By applying long, narrow, swann-neck designed columns. Narrow collums that increase vapour speed, so the smearing they look for can actually be accomplished. Remember higher vapour speeds are needed to transfer Tailsy molecules from the boiler to the final product.
Scotland versus the rest of the world
Scotland versus the rest of the world? Let me re-write that into: “Scotland vs. Germany”. Remember my posts about boiler design? And about how Craft Distillers from around the world not only wanted to buy BMW and Mercedes cars, but also shiny German distilleries? And if they can’t afford them … one of their Chinese clones? Well, that’s the match we are actually watching here.
Scotland – Germany? No, let me rephrase that again. Whiskey still versus fruit brandy still. Doesn’t that make sense to you? In that case, please read my two posts on boiler design first. If you do, for sure the above remark will make sense.
German still manufacturers conquered the world by selling Craft Distillers on all continents fruit brandy stills. Do you remember that this causes many of today’s Craft Distillers to run stills with boilers that are designed sub-optimal? Well, let me enlighten you on something else. Fruit brandy columns aren’t that well suited for whiskey making either. Neither are they suited for rum and vodka making, and only partially do they support making brandy from wine. But that deserves a new post. That will be in “Odin on Whiskey Column Design (2)”. You want me to lift the veil a bit? Okay, here we go. Remember those fruit brandy stills have boilers that are too narrow and high for efficient distilling? Well, fruit brandy columns are actually too wide …
Enough for now. You have some reading to do. And I am off to bed!