Tuesday Tech Talk!


This Tuesday Tech Talk post is about still design. A change in still design paradigm and the importance of cooling, to be more precise.

Change your paradigm!

Most look at a still and see a boiler feeding gases to the column. When I look at a still, I see a column sucking gases from the boiler.

A well-designed still isn’t based on the boiler pushing gases into the column, but on the column “inhaling” gases provided by the boiler. A “pull through” rather than a “push through” model.

Pro’s and Con’s

A boiler trying to push gases through the column creates microbursts of overpressure. Two negative consequences are the result. First of all the pressure microbursts change the vapor speeds. Vapor speeds define the amount of late Heads and early Tails smearing into your Hearts cut, so you want to keep them as stable as possible, in order to be able to let your still harvest the right flavors.

The second problem with pushing gases into the column, is that the associated pressure microbursts create unmanaged and unwanted boiler reflux. Some of the gases do not travel up into the column, but shift phase and become liquid again … and fall back into the boiler.

When a still design is based on the “pull model”, where we see the column as a means to gently suck up gases, we create a more effective and efficient system:

  1. A pull model design is more effective because it allows the master distiller to harvest the right taste;
  2. A pull model design is more efficient since it minimizes boiler reflux.

Designing a pull model still

The design of a pull design still is based on three corner stones:

  1. A wide, insulated and angled boiler;
  2. A non-pressurized column;
  3. A 100% effective column cooler.

A well-designed, wide boiler creates a stable gas bed, that allows the column to suck in gases freely. The insulation and right angles further prevent boiler reflux.

Since the column manipulates the gases, drag (or autonomous pressure) is created. We want to minimize that and therefore created a non-pressurized column. iStill columns can’t be pressurized (unless they are maltreated) and that gives a huge advantage, because it allows the whole column to suck freely.

One liter of low wines, when boiled, results in 1,200 liters of gases. If we don’t cool these gases down adequately, there is a huge risk of creating overpressure (especially in columns that do not have anti-overpressure designs – see above). That’s why iStill opts for a column cooler that cools down all gases at the very top of the column. The cooling down actually creates the pull at the top of the column that has the gases enter at the bottom. It’s the perfect and complete cooling at the top, that creates the suction at the bottom!


If you design (and operate!) your still as a “pull through” model, you will get over better taste with less effort and energy.





4 thoughts on “Tuesday Tech Talk!

  1. Very interesting read, as always! Will all robotised units share the same column cooler design (that looks like a Dephleg) as the 2000l pot?

    Another question: what is the difference between the cooling head on the old iStill (wound ss tubing, I think) and the new cooler. I know the obvious difference, in design, but just interested how it impacts still performance. Apologies if this is a dumb question or you’ve blogged on it before.

  2. Yes, they will, Craig. So far the 2000 uses the new shotgun cooler where the 500 uses the older style with wound ss tubing. The wider diameter needs the upgraded column design. In the future I foresee the iStill 500 also will use this new tech for reasons of standardization, even though it works fine as it is right now.

    • Thanks for the reply Odin. I was doing some reading on HD regarding cooling etc. and just wondered if there was any technical benefit the shotgun brought over the wound SS. I can see how on the larger diameter units. Never mind. Keep up the great tech posts anyway.

      • The advantage is bigger cooling capacity, more open space and a more even spread of the open space. All important on the bigger columns, not a nececity on the 5 and 3 inchers.

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