On boiler design, agitation and taste!


This is both a theoretical and a practical post. Theoretical, because I will dive in deeper on how a boiler should be designed to work optimally. Practical, because I have put the theory to the test by actually designing and building, according to those principles, the non plus ultra boiler for the new iStill 500 NextGen.

Boiler design and taste

The role a boiler plays in any distilling device, when maximizing taste is the goal, is twofold:

  1. Does the boiler enhance the formation of taste molecules (esters) during distillation?
  2. Does the boiler provide these taste molecules to the column in such a way that they can be harvested easily?

I have discussed the second point extensively in a previous post. The summary? A wider, rather than a more narrow, boiler design creates a more stable gas bed above the liquids. A more stable gas bed positively correlates with the columns ability to harvest the right tastes in an efficient and effective way. If you want to read more, please do a search on “boiler design”. As for now … let’s look at the first point: how can boiler design enhance the formation of taste molecules during the distillation process?

Taste formation while distilling

Most of the taste of any taste richt product, like rum, whiskey or brandy, is created during fermentation. Even though the distilling part of the process is more about taking out (Headsy and Tailsy) tastes, distilling can actually add up to 20% of taste. If (and that’s the important word here!), if that boiler enhances the Maillard Reaction as well as the process of esterification.

Esterification is the creation process of taste molecules, also called “esters”. Esters are formed where alcohol and organics meet in a wet and sour environment. Read: where grains and alcohol or molasses and alcohol or fruit and alcohol or berries and herbs and alcohol meet. Water is the medium that helps the organics and alcohol join. Sourness increases the esterification reaction, as does heat.

In plain English? For a boiler to actually help you create more taste, it must have the capability to deal with organics.

The Maillard Reaction is a caramalization process that creates a taste cascade. It is triggered by temperatures close to 100 degrees Celsius (and a few other things) and enhanced by slight temperature differences in the boiler. To get these temperature differences, you need a directly fired still. Indirectly heated stills have perfect temperature distribution and therefore hamper the Maillard Reaction.

Again – and in plain English – you need a direct fired boiler to create taste. A directly fired boiler that can handle organics.

Odin’s teacup paradox

One day, when stirring some sugar into a cup of tea, it struck me: the way agitators and boilers are designed is not right. This is what happened. I had a round glass of hot tea, I poored in some sugar, and I stirred quickly. Where I expected the sugar to be distributed more evenly throughout that glass of tea, it actually didn’t. Instead, I could witness two things happening:

  1. A vortex was created, pushing the liquid down in the center while pushing it up near the edges of the glass;
  2. The sugar gathered in the center of the glass and did not disperse evenly at all.

Like this:


Stirring at high rpm in a round glass or boiler creates a vortex and centralizes particles. A vortex is bad, because it disturbes the gas bed above the liquid and because it severely limits the maximum filling charge a boiler can take. Particle centralization (instead of perfect particle distribution) potentially creates burn issues.

The NextGen boiler design

I wanted the NextGen boiler to solve my teacup paradox, and this is what I did: I created a flush square (and patented!) design. The flush part helps circulation, where 90 degree angles would have hampered it. And the square design actually breaks up the vortex. And more! The four corners of the flush square boiler design act as “chimneys”, sucking up grains from the bottom and redistributing them to the top.

Instead of a vortex, with centralized particles, the new boiler design and agitator create a stable liquid bath with perfect particle distribution!

Like this:


Movie …

As the proof of the pudding is in eating, the proof of perfect boiler design and agitation is in seeing it happen before your own eyes … so here’s a short movie. It will show you how the new boiler design and agitator work together to prevent vortex formation and particle centralization. If you look at the four corners of the boiler, you can even see the chimney effect:


3 thoughts on “On boiler design, agitation and taste!

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