Can Your Still Really Produce 99.9% ABV?
A new distiller recently got the sort of result that would make almost anyone take a second look at their alcoholmeter. During a spirit run through a reflux still, the instrument appeared to be showing 99.9% ABV. About 2.5 litres had already been collected.
It sounds impressive. Unfortunately, if you are producing ethanol and water using ordinary distillation, a reading around 99.9% is almost certainly telling you something is wrong with the measurement, not that you’ve discovered a miraculous still.
Why 99.9% ABV is a warning sign
Ethanol and water form what is known as an azeotrope. Under normal atmospheric pressure, conventional distillation reaches its practical limit at approximately 95.6% ethanol by mass, corresponding to roughly 96% alcohol by volume.
At that point, ethanol and water effectively distil together and further ordinary redistillation won’t simply push the spirit to 99 or 100% ABV.
Producing genuinely near-anhydrous ethanol requires another dehydration process, such as molecular sieves.
So if your alcoholmeter suddenly tells you that your reflux still is producing 99.9% ABV, don’t immediately celebrate. Check the measurement.
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Temperature is usually the first suspect
This particular mystery had a very simple ending.
Once the collected spirit had cooled, the reading dropped from the apparent 99.9% to “93% ABV”.
That is an entirely believable result from a home reflux still.
Most alcoholmeters used by home distillers are calibrated at a specified reference temperature, commonly 20°C. Their readings are based on the density of an ethanol and water mixture.
Change the temperature and you change the density.
Put an alcoholmeter into warm spirit straight from the still and the reading can therefore be significantly different from the true ABV.
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The simple rule is:
Know the calibration temperature of your alcoholmeter and either measure the sample at that temperature or use an appropriate temperature correction.
Don’t assume the number you see on a floating alcoholmeter is automatically the actual alcohol percentage.
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Check your alcoholmeter as well
If a reading looks impossible, check the instrument before blaming the still.
A useful basic check is clean water at the alcoholmeter’s calibration temperature. It should read approximately zero alcohol. Check the instrument for physical damage and make sure it can float freely without touching the sides or bottom of the measuring cylinder.
Cheap alcoholmeters aren’t laboratory instruments either. Small discrepancies are perfectly normal.
For most home distilling purposes that isn’t a serious problem. Knowing whether your spirit is around 92%, 93% or 94% is generally far more useful than pretending an inexpensive hydrometer can tell you whether it is 93.17%.
What should come out of a reflux still?
There isn’t one magic number because the result depends on the design of the still, column packing, reflux ratio, boiler charge, operating technique and collection rate.
However, spirit in the 90–95% ABV range can be perfectly reasonable from a properly operating home reflux still.
Reaching the upper end generally requires an efficient column operating under good reflux conditions.
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And there is another important lesson here: faster isn’t necessarily better.
Driving a reflux still hard may increase the amount of spirit coming out per hour, but it can reduce the separation occurring inside the column. Giving the column sufficient reflux and controlling the take-off rate can produce cleaner, higher-proof neutral spirit.
The objective isn’t simply to make alcohol come out of the condenser as quickly as possible.
Hot spirit deserves attention for another reason
Incorrect ABV readings aren’t the only reason to pay attention to product temperature.
High-strength ethanol is highly flammable and warmer ethanol produces more vapour. Your product condenser should be capable of completely condensing the vapour entering it and delivering liquid spirit safely.
If high-strength distillate is emerging unusually hot, investigate your cooling arrangement rather than simply accepting it as normal operation.
Adequate ventilation, no ignition sources and properly functioning cooling equipment are fundamental whenever high-proof ethanol is being produced.
Don’t confuse alcoholmeters and hydrometers
This catches plenty of beginners.
A brewing hydrometer measures the density of a fermenting wash and is commonly used to estimate fermentation progress and potential alcohol.
An alcoholmeter is designed to estimate the alcohol concentration of a relatively pure ethanol and water mixture.
Once substantial quantities of sugar, flavouring, extracts or other dissolved substances are present, a simple alcoholmeter reading may no longer accurately represent ABV.
For freshly distilled neutral spirit, however, it is exactly the sort of instrument commonly used.
The 99.9% reading actually taught us a useful lesson
In this case, the first-time distiller hadn’t somehow broken the laws of chemistry.
His apparent 99.9% ABV became about 93% after the spirit cooled.
And 93% from a first reflux spirit run is nothing to be embarrassed about.
More importantly, the experience demonstrates one of the easiest mistakes for newcomers to make: an alcoholmeter reading is only meaningful when you understand the conditions under which it was taken.
So next time your still appears to have produced almost pure ethanol, resist the temptation to declare yourself a distilling genius.
Let the sample reach the correct temperature.
Then measure it again!
Until next time… Happy Distilling!
Cheers
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