3 Ways to Manage a Reflux Still Column

Understanding and managing a reflux still column is just one of the basic skills needed to operate distillery equipment. Balancing the temperature and alcohol by volume (ABV) is important when managing the performance of the reflux column still. Adjusting the reflux temperature can control the ABV, making it increase or decrease. A reflux column can consistently distill a high concentration of alcohol from a mixture that only has 8% or even 1% alcohol.

Here are three useful ways that a distiller can monitor ABV progress throughout the run:

• Temperature principle (TP)
• Concentration principle (CP)
• Vapor-llquid equilibrium graph

Temperature Principle (TP)

Under the normal atmospheric pressure, the water boiling point is 100°C / 212°F, and the anhydrous (no water) ethanol is 78.4°C / 173.1°F. Since ethanol is infinitely miscible with water, the mixture’s boiling point will be somewhere between 78.4°C / 173.1 and 100°C / 212°F. As the mixture begins to boil, the components with the lowest boiling point will begin to vaporize first (typically the highest ABV concentration). As product collection during the run continues, the kettle temperatures gradually increase as the kettle charge composition changes. To ensure that you are getting optimal separation, it is recommended to slowly heat the kettle. 

Why do we need to know the relationship between the vapor temperature at the top of the apparatus and the boiling point? Because this relationship can help the distiller to determine the remaining amount of alcohol in the kettle. This also helps the distiller understand when to increase the reflux ratio in order to ensure that the requisite ABV is being rendered.

If, for example, 90°C / 194°F is the optimal head temperature for your reflux still column to collect alcohol, if the temperature increases during the distillation, the distiller can increase the reflux ratio and thereby increase the amount of ABV being sent over to the product condenser. Without an increase in reflux ratio (RR) the concentration / ABV of the distillate will decrease.

On the other hand, when the head temperature drops below the ideal temperature to separate the ethanol and water, the concentration / ABV will be higher. To resolve this problem, the distiller can reduce the reflux ratio and thereby reduce the ABV of alcohol collected as finished distillate.

Concentration Principle (CP)

The concentration principle is predicated upon the notion of positive feedback that occurs with multiple phase change cycles. For spirits distilling purposes, each time a water / alcohol mixture goes from its liquid state to gaseous state, this is phase change. And, from gaseous state back to liquid, is also phase change. Therefore, after one full cycle of phase change, the subsequent liquid rendered will always have a higher ABV content, as a percentage of water within the mixture is left behind during this mass transfer to the next higher plate on the column.

As the plate fills with enriched alcohol, the overflow will drain downward to the next plate level down. This overflow from above will also have a higher ABV compared to the liquid currently on the plate.All the while, the reflux condenser will condense a percentage of vapor to be sent back to the very top plate. This returning reflux will have a higher percentage of alcohol than what is currently on the plate.

We then have the plates being enriched from above as an alcohol-rich measure of liquid is being returned and distributed down to the next lowest plate level. while the distilling column is also being simultaneously fed alcohol from the kettle, and then being purified by way of phase change cycles that occur during mass transfer toward the top of the distilling apparatus.

This technique of enriching or concentrating the alcohol content with the reflux condenser at the top of the distillation apparatus while slowly drawing off distillate to maintain a high level of ABV during the run is the essence of the concentration principle. Careful and deliberate operation of the equipment can create a consistent ABV in the vapor, allowing the distiller to replicate flavor profiles over the course of multiple runs.

Vapor-Liquid Equilibrium Graph

Using an alcometer at the distillate discharge of the column can help the distiller understand what ABV of the distillate is. To run more efficiently and precisely, distillers can formulate an ABV rough estimate throughout the run using the different temperatures available. A vapor-liquid equilibrium graph is helpful to estimate the ABV in the reflux still column.

Collecting correct temperatures is an important factor in estimating the ABV during the run. You will need a thermometer at the top of the vapor path, after the dephlegmator (reflux column still condenser), and a thermometer to measure the liquid mixture temperatures in your kettle.

As always, should you have any questions or concerns regarding the use of your StillDragon distilling equipment, please don’t hesitate to contact us.