Introduction

We stack our columns on top of our boilers, here, at iStill. We don’t do side-mounted, off-set, floor-mounted columns. Many still manufacturers do. Why do they offer off-set columns and why don’t we? Let’s dive in deeper …

Why some manufacturers provide off-set column stills

The reason why still manufacturers offer off-set columns is simple. By placing the column next to the boiler, instead of on top of that boiler, the total still is lower. And lower stills fit in places with lower ceilings. There you have it: the reason for off-set columns is to allow distillers with height-restricted distilling halls to get a still anyhow.

Before we dive in at what costs off-set columns come, let’s see how they are build. A deeper dive on the engineering behind off-set column potstills, so to speak.

Engineering an off-set column still

As the liquids are brought to a boil inside the boiler, gasses are produced that – normally – would travel vertically upward. Because, in an off-set column design, the column does not sit directly above the boiler, these gasses have to be rerouted from the top of the boiler to the bottom of the off-set column. This is done via the so-called vapor return line (see picture underneath).

The vapors are presented to the off-set column just below the lowest plate, at the column entry point (see picture below), via the aforementioned vapor return line, that usually runs at the back of the column downwards. From there, the gasses travel upwards and are redistilled on the plates above.

The processed and higher proof gasses now exit the column at the column exit point, from where they are transferred to the product cooler. The now distilled spirit leaves the still at “product out”. The reflux, that is created during the refining process, exits the column at the base of that column, via the reflux return line. Please note that, for the reflux to be able to flow back to the boiler, the off-set column still needs to be raised from the floor.

Traditional, off-set column still design …

Why we do not offer off-set column stills

There are three major reasons why we do not design, produce, or sell off-set columns at iStill. They have to do with the influence this design has on:

1. Vapor flow separation;
2. Vapor speed acceleration and deceleration;
3. Boil distribution and vapor production localization.

I’ll explain each of these subjects in a dedicated paragraph in the remainder of this iStill Blog post, before I finish up with how the iStill handles ‘m and then some conclusions. But first I’ll need to explain laminar vs. turbulent gas flow to you; and why this is key to an optimized still design.

Laminar vs. turbulent gas flow

Laminar gas flows are smooth and streamlined, whereas turbulent flows are irregular and chaotic. In distillation, in order to create high-quality spirits, we need to separate the right amount of heads and tails from the hearts faction. The better we control the amount of heads and tails that can smear our hearts, the higher quality our newly made spirits will be.

Heads, hearts, and tails – or any mixture of ‘m – come over at different vapor speeds. If you distill at lower vapor speeds, heads will come out first, with hardly any hearts contamination. If you distill at higher vapor speeds, tailsy alcohols and esters come over earlier. Higher vapor speeds result in more tails smearing into hearts at an earlier phase of the distillation process.

A laminar gas flow is constant, efficient, and well-organized. A turbulent gas flow is variable, inefficient, and easily mixes headsy, heartsy, and tailsy components all together, because of the vapor speed differences in that turbulent environment! An optimized still design therefore aims to create a laminar gas flow, where a sub-optimal still design creates a turbulent gas flow. An optimal still design offers stable vapor speed so that you, the craft distiller, get to decide on cuts. A sub-optimal still design offers all kinds of vapor speeds. It presents you with de facto smearing, instead of empowering you to make better spirits by controlling the amount of smearing you look for in a certain spirit!

We have now established the overall goal of still design: a great still offers the craft distiller a laminar gas flow, which results in control over smearing. We also defined what makes for a bad still design: a bad still offers the craft distiller a turbulent gas flow, that offers a predefined, high amount of smearing. With that in mind, let’s see why off-set columns suck.

Laminar vs. turbulent columns …

Vapor flow separation

Vertical lines or pipes result in a steady vapor flow upwards. But when we start to bend those lines, something weird happens: the vapor flow starts to separate from the line wall. And as flow separation sets in, turbulence is created at the corners. Vertical columns and lines allow for laminar gas flow, where bended columns or pipes or lines result in vapor turbulence. What we can learn from this? Straight pipes perform better!

Bended lines lead to vapor flow separation in the corners …

If you take another look at the traditional, off-set still design, please count the number of bends the vapors have to deal with. There are seven corners, seven turbulence creators the vapors have to deal with:

1. The vertically rising vapors from the boiler are pulled into the vapor return line at a 90 degree corner;
2. The now horizontally traveling vapors are directed downwards in another 90 degree corner;
3. The now vertically descending vapors enter the column at the column entry point … horizontally;
4. Once they get spit out from the vapor return line they bent another 90 degrees: upward in the column;
5. After they are processed in the column, the now vertically rising vapors are pulled towards the cooler at 90 degrees;
6. The now horizontal vapor flow is once more cornered via a 90 degree bend downwards into the cooler.

That is a total of six times 90 degrees or 540 degrees. That equals a whopping one-and-a-half spin in total! Imagine the associated turbulence that these bends create. And how that turbulence disrupts the otherwise laminar gasflow … smearing heads, hearts, and tails into one another. And that’s just with six out of the seven corners mentioned. The seventh will have to wait a bit. First, I want to dive into the influence of vapor speed acceleration and deceleration.

Vapor speed acceleration and deceleration

A pipe that’s vertical and of the same constant diameter will support equal vapor speeds throughout its design. But vapors that travel through pipes or columns of varying diameter will speed up in the narrow sections, while slowing down again at the wider parts of the design. Like this:

A straight pipe of overall equal diameter results in equal vapor speeds and laminar gasses. A pipe with bottle-necks results in a wide variety of vapor speeds, resulting in a much more turbulent gas flow.

If you take another look at the picture of the traditional, off-set still design above, how many bottle-necks do you see? How many reductions and expansions do you count. Here are six:

1. Boiler to riser (reduction => vapor speed increase);
2. Riser to spat ball (expansion => vapor speed decrease);
3. Spat ball to vapor return line (reduction => vapor speed increase);
4. Vapor return line to column (expansion => vapor speed decrease);
5. Column to cooler (reduction => vapor speed increase).

We can count a total of six bottle-necks, where vapor speeds slow down (and increase pressure) and then speed up again (resulting in lower pressure). It is easy to see how these rapid and huge changes in vapor speeds create tremendous amounts of turbulence. And there’s just five of these events mentioned above. The sixth and final one will have to wait until we dive into boil distribution and vapor production localization, which we will do underneath. Oh, wait, first we need to look at the double pile-on effect!

Intermezzo 1: the double pile-on effect!

Remember how bends create vapor flow separation? Guess what ultra-high vapor speeds do in bends? They separate even more. Easy to imagine, if you envision racing cars trying to make a corner on the circuit that they are racing: the faster the cars go, the more will crash and not make it through the corner!

What the double pile-on effect is here? Fast moving vapors result in more vapor flow separation. It’s an easy equation. As a rule of thumb vapors that travel twice as fast, cause twice the turbulence. Let’s do some calculations!

A straight round column of 20 centimeters diameter has a surface area of 10*10*3,14 equals 314 cm2. In order not to make the calculations too complex, let’s assume the vapor speed in that column to be X km/h. Now, let’s look at what happens if we push the vapors from a 20 centimeter diameter pipe into a 2 centimeter line (for example from the riser or spat ball into the vapor return line). What do you expect? A 10 time increase of the speed inside the vapor return line? Read on to be amazed …

The surface are of the 2 centimeter diameter pipe is 1*1*3,14 equals 3,14 cm2. The pipe can handle only 1% of the throughput of the 20 centimeter column it got fed from! The speed in the pipe is therefore (leaving pressure build-up, with its own cascading effects on turbulence, outside of this picture) be 100 times higher than in the column … resulting in a 100x larger amount of turbulence AKA uncontrolled smearing!

Do you start to see why a traditional, off-set still design is sub-par? Why it underperforms? How and why it results in unwanted – because uncontrolled – smearing of heads, hearts, and tails? And how one fault can aggravate another to the extend that they reinforce one another, causing even more issues combined? Bends create turbulence. Speed variations create turbulence. High speeds and bends combined result in higher turbulences than the two contributing factors on themselves. If not, if it is not yet clear, please read this iStill Blog post again. If you do get it, please continue.

Gas trajectory in black, reflux in red, spirit produced in green, beer or wine in yellow …

Boil distribution and vapor production localization

An even distribution of the boil results in an even production of vapors over the complete surface area of the boiler. Even vapor production leads to a stable gas-bed above the liquids, from which the riser/spat ball/column (in fact: the cooler) can draw. A stable gas-bed, in other words, empowers a laminar gas flow. An unstable gas-bed results in turbulence.

Now take a look at the reflux return line on the traditional, off-set still design in the picture all the way up, at the beginning of this article. That reflux, that is returned from the column to the boiler via the reflux return line, is quite a bit cooler than the liquids in that boiler. First of all, because the reflux is higher proof than the boiler contents. Secondly, because the reflux liquid has been managed by an uninsulated copper (very conductive!) still … cooling it down even further, before it re-enters the boiler.

The problem? The colder reflux is returned to the boiler at the side. This results in the left side of the boiler contents being cooled. The consequence is that the left 25 to 30% of the boiler does no longer boil and does not produce gasses. Only the remaining 70 to 75% of the boiler (the middle and right side) produces gasses. Where do these gasses go? In an optimal design straight up into the riser or column. But that’s not the case here!

As the left side of the boiler in the above design does not produce vapors, the gas-bed above the liquids is unstable. The vapor pressure is higher in the middle and the right upper side of the boiler, than it is at the non-productive left part of the boiler, resulting in the gasses taking a turn to the left, and filling that void, before they can enter riser or column!

There you have it: there is another bend in the vapor flow (number seven!) and there is another speed differentiator (number six!). And these two are very important, because they exert a tremendous influence. Why? Because they happen in the boiler. Where the primary gasses are produced, that directly distill off the taste rich beer or wine. It’s not just the bends and speed differentials that severely hamper the ability for this still to produce high-quality spirits, it is already compromised from the get-go, from the initial evaporation cycle onwards. Another double pile-on effect? For sure! And remember: garbage gasses in equals garbage liquids out!

Intermezzo 2: how the iStill produces a laminar gas flow

The iStill is designed to provide stable vapor speeds, so that the craft distiller can decide (and control!) the amount of heads and tails smearing into his hearts faction. Allow me two examples to elaborate. A fruit brandy needs fruit forward flavors, that are heads associated. These flavors are fragile. More fragile than tails-associated flavors. The craft distiller would want to distill slowly, with low vapor speeds, so that he can perfectly control the heads faction and the amount of smearing into hearts, without having the tailsy flavors coming over too soon.

Another example about that same craft distiller that now wants to make a whisky. He wants some heads smearing to provide his whisky with a fruity front-of-mouth taste. He does want a lot of back-end flavor, that the tails provide. he will choose for a higher power setting and higher vapor speeds in order to achieve that. If he has an iStill, that is, because with a traditional still one cannot really influence vapor speeds that much.

So, how do we make sure we deliver a laminar gas flow? Let’s use what we learned above. First, we do not have bends. Gasses travel up, get cooled down via the column cooler, and are scooped out on their way down. The gasses simply ascend, until they are converted back to liquid phase, and then they fall down. Did I already mention that the iStill provides a gas trajectory without any corners? So … instead of seven turbulence creators … we have none! Instead of seven uncontrollable smearing causative agents … iStill has zero.

Speed variations? We have one instead of six for the old and traditional still design. The only speed variation we have is when gasses get sucked up into the column, from the gas-bed underneath. And as our gas-bed is non-disturbed, that’s just fine.

Does iStill have a stable gas-bed? Yes it does! The reflux that we create in the column falls back through the center of the column into the center of the boiler! And it only does so after being further rectified and heated up in the reflux capacitor, so that the reflux, as it enters the boiler, has the exact same temperature and does not disturb the boil.

A lineair column without bends or restrictions …

Gas trajectory in white, reflux in red, spirits produced in green, beer or wine in yellow …

Conclusion: why off-set, floor-mounted columns suck!

They suck because they provide seven places where vapor flow separation creates huge amounts of turbulence. Even a traditional copper column with a column mounted directly on top of the boiler would limit the number of turbulence causes to three or four, rather than seven, like the off-set model gives you.

Off-set, floor-mounted columns suck because they they have six vapor speed acceleration and deceleration zones, that – each and every one of them – are six more causes for more turbulence. And you know by now how turbulent gas flow screws up your cuts, right?

Finally, off-set columns – via their side mounted reflux return line – significantly disturb the formation of a stable gas-bed for the column to draw from. From the first evaporation onwards, the whole distillation process is already compromised as the column is fed not by a steady stream of laminar gas, but by a fluctuating and turbulent gas-bed.

Why does iStill not sell an off-set, floor-mounted column to help with height-restriction?

Because off-set, floor-mounted columns suck.