Aspects of Distillation (4): Boiler Design!

20 April 2020
Introduction Aspects of Distillation” is a series the iStill Blog hosts. It aims to cover as many aspects as possible. Aspects of – you guessed it! – the distillation process. Think alcohol formation, flavors, mashing, distillery design … and more. In fact, if you have a suggestion, please email us the aspect you want us to dive into. Via Today’s topic? The influence and importance of a well-designed boiler. Boiler Design There are three things I want you to consider, when investigating the importance of the boiler design of your still for the distillation process:
  1. Shape;
  2. Material specifications;
  3. Heating source.
A wide boiler provides a bigger surface area than a narrow/high design, resulting in a less aggressive boil and a stable gas bed from which the column can draw. The less aggressive boil results in higher filling grades. The more stable gas bed results in more constant vapor speeds that lead to less (uncontrolled) smearing and better control over heads, hearts, and tails cuts. A round boiler is the least ideal shape, because it will let the agitator spin the wash. The faster the wash rotates, the less effective the actual mixing becomes. Also, the rotation will create a vortex, that results in lower net filling levels and a very turbulent gas bed for the column or riser to draw from. Baffles can prevent wash rotation, but come with their own set of issues. Most importantly so-called "slow spots", where no mixing takes place and filth builds up. The perfect boiler shape for a boiler is flush square. The "flush"-part helps the wash move along through the boiler, while the "square"-part of the equation prevents vortex formation, uneven particle distribution, and gas bed disturbance. Longevity and chemical resistance are important, when designing (or choosing) a boiler. Stainless steel is the material of choice. A boiler needs to be over designed to deal with the life long harsh hot/cold treatments that distillation cycles basically are (when seen from the perspective of the boiler). When your still has a double boiler, you probably heat it with steam or oil. A double boiler system, AKA "au bain, Marie!", evenly heats the wash. A directly fired boiler creates slight temperature differences in the boiler that trigger the Maillard Reaction. The Maillard Reaction is a sugar browning reaction, that results in a taste cascade of 25% more flavor. And that is something you do not want to miss out on, as a craft distiller! So guess what? You want a wide and flush square boiler, that is over designed and directly fired. Features & Benefits All iStills have wide, flush square boilers, made out of 3, 4, and 5 mm thick stainless steel. You now know why ...



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