Regarding Reflux ...

12 October 2021


Reflux ... what is it and what role does it play in distilling? Let's dive in deeper and find out more on this important topic!

A definition of reflux

Gasses that phase-shift back to their liquid form, and fall or flow back down towards the boiler are called "reflux". There you have it: the definition.

If you look at it again, please note that reflux is always liquid and that it does not leave the still. The liquids that leave the still are called "product" or "spirit" or "new make" or, well, maybe "gin", depending on what you are making.

How reflux is made

Gasses that rise up from the boiler enter the column or riser of the still. As they meet a cooler environment, some of these gasses phase-shift back to liquid state. As liquids are a 1000 times heavier than gasses (as a rule of thumb), these liquids or "reflux" will fall down.

In a potstill the reflux falls back down into the boiler. In a column still, the reflux gets picked-up by the column's packing or plates for further processing. What are the advantages and disadvantages to creating reflux? A good question that we'll answer underneath. But first let's explain the different varieties of reflux that exist.

Two types of reflux

There are basically two types of reflux:

  1. Passive reflux;
  2. Active reflux.

Passive reflux is created as a result of how stills are build. It is - so to speak - a given. Gasses inside the column or riser of any still are hot. At between 78 and 99 degrees Celsius, the inside of the column is much warmer than the outside, AKA your distilling hall. To turn your perspective around: the cooler distilling hall works as a heat-exchanger on the gasses inside the still. The room cools the metal that makes up your still. The now cooler still condenses part of the gasses on the inside, turning them into passive reflux.

Active reflux is intentionally created by the distiller. In a cooling management kinda still (traditional fruit brandy still with plates), he or she can use the dephlagmator to cool more gasses down to reflux. In a more advanced liquid management solution, like the iStill, the distiller can decide (or have the iStill decide) on how much reflux is created and returned down the column for further processing.

Disadvantages of reflux

If not all gasses make it over into the product that you are making, isn't that an inefficiency? Yes, it is. The disadvantage of creating reflux is inefficiency. A non-insulated still looses a lot of energy to passive reflux, that falls back into the boiler and basically now needs to be distilled again.

So ... if reflux is an inefficiency, why accept it or even actively create it during a distillation run? The simple answer is: because it does also creates some benefits.

Advantages of reflux

Reflux can be created and reflux can be actively managed. If you have a column with plates or packing to catch the reflux, that is. Reflux that just falls back into the boiler, well, that doesn't help the distillation process in any way, but reflux that lands on column packing or plates does make a difference.

Reflux that is picked-up by packing or plates is both spread out and slowed down. Both processes allow the reflux to mingle with the alcohol vapors that rise from the boiler. As the gasses and reflux meet and mingle, they exchange molecules. As follows: water and higher boiling point alcohols will move from the gasses into the reflux. Remember that the reflux is heading down the column (where it is hotter), and water and high boiling point alcohols need higher energy inputs (hotter environments) to stay in gas-phase and in an upward movement.

Ethanol and lower boiling point alcohols tend to jump over from the reflux to the lower energy state rising gasses. This makes scientific sense, since these compounds need less energy and stay in gas-phase at lower temperatures, and as the gasses are rising and redistilled, the temperatures higher-up in the column are cooler.

The result? Actively created and managed reflux creates a higher alcohol percentage of the product that does come over. It also helps separate heads, hearts, and tails better.

Potstills and passive reflux: an example

Potstills do not actively manage their columns or risers. Any reflux produced is by definition passive reflux. In very slow runs, with an uninsulated riser, a steady downstream on the inside of the riser's material can be created. This results in some molecule-exchange between reflux and rising gasses. Especially when the potstill's riser is made from copper, which is very conductive, more passive reflux can actually create a slight boost in ABV and slightly better separation between heads, hearts, and tails.

There are two problems associated with trying to work with passive reflux in a potstill. The costs in terms of energy and efficiency losses are humongous. Secondly, the process is incontrollable. In winter you'll get more passive reflux than in summer, simply because the colder distilling hall provides more cooling.

iStills and active reflux: an example

iStills are insulated, so if we run an iStill Hybrid in potstill mode no passive reflux is created. Yes, it is that simple: no temperature differential between distilling room and the inner-boiler - via the application of robust stainless steel and advanced insulation - prevents the formation of passive reflux.

By selecting the iStill Potstill Program, the distiller can choose how much he wants to open the robot that controls output. If he decides to go for a big opening, all product will come out and no reflux is created. Potdistilled and efficient. Does he or she decide to go for a smaller opening, more reflux is created and returned down the column. As a result of our innovative design, the exact amount of separation of factions and concentration of alcohol can be achieved, at maximum efficiency!

Now let's move to the iStill Column Program. The distiller for example chooses to make rum in one go. The 10% wash needs to be brought to 62% for barrel aging. He or she can now simply tell the iStill what percentage the product needs to come over. The robot will actively manage the amount of reflux needed to keep the product flowing at 62% ...

Reflux on an iStill Plated Still ...


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