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While consulting for FIVE x 5, I’ve been lucky enough to meet distillers from all walks of life, and at all stages of the learning process. One of the appealing things about this industry is that you can always learn more – I’ve been doing it since 2018 and I still learn something new most every week.
With that in mind, allow me to get into the weeds a little bit on a frequently-misunderstood topic: boiling points, methanol, and separation in distillation.
Many distillers believe in a falsehood about the chemical properties of fermented mashes/beer and spirits. The falsehood states that lower boiling-point components of your beer (for example, methanol with a boiling point of 148.5F) will independently and separately “boil off” or evaporate while leaving behind higher boiling point compounds like ethyl alcohol (173F) and water (212F). I have heard, more times than I can count, a distiller claim that they leave the still manhole open (or discard collections) when the pot liquid is under 173F, with the express purpose of eliminating methanol and/or higher boiling point compounds from the final product.
This mental picture of different components independently boiling at their respective boiling points is correct when you have liquids that do not mix. For example, if you put a 50/50 mix of olive oil and water into a still, the water component would boil at around 212F, leaving behind most of the olive oil, which would probably never hit it’s 570F boiling point. (Pedantic note: some of the oil would carry over with the water – this is how essential oil distillation works. It is a mechanical carry-over effect rather than vaporization of oil.)
The nature of ethanol, water, methanol, and most other alcohols is different. When you combine them, they form what’s called a miscible solution. A miscible solution is homogeneous by definition. The key to understanding miscible solutions is that they have their own boiling point and other chemical properties, arising from the relative concentrations of the components. They stop acting like ethanol or water and start acting like a blend of the two, with properties in between the properties of those components. In typical beverage distillation, the properties of the miscible solution are dominated by the effects of the ethanol and water, since all other compounds are present only in trace quantities. Nonetheless, these trace quantities also affect the boiling point and other properties of the mixture.
Consider a mixture of ethanol, water and trace alcohols, testing at 50% ABV. This liquid has a boiling point of about 180F. Until your still reaches 180F, none of the liquid is evaporating. (This is the stage where distillers mistakenly believe that methanol is independently separating).
Once it reaches 180F, all components (ethanol, water, methanol, etc) begin boiling simultaneously (remember, it’s a homogenous solution) and carry over to your collection. Alcohols and other compounds wind up concentrated in the collected fractions, while water winds up concentrated in the stillage (leftover in the pot). If there is methanol in your beer, then there is methanol in your collected spirits. And, there is almost certainly more methanol (percentage-wise) in the distillate compared to the beer. After all, distillation is a purification (concentration) process. This is a fact that may be hard to hear. This means that the distiller’s primary job – making cuts – is mostly about flavor and not about purification or separation. You do not have as much control over the distillate’s composition as you may think you do.
The only time this is untrue is if you have a “demeth column”, which is only found at large alcohol plants and costs millions of dollars. Even at that expense, a demeth column is only able to remove a couple dozen PPM of methanol from the final product.
You might be saying, “well, that’s true for a pot still – but we have a column!”
I’m here to tell you that it doesn’t really matter. You are still collecting a blend of components in your distillate, unless you have the aforementioned demeth column. With a column, you may be able to capture a bit more methanol in your heads draw, compared to a “cut” on a pot still, but you’re still playing in the margins and you’re still collecting lots of non-ethanol compounds in your “hearts”.
For some semi-scientific backing, there are some interesting threads on homedistiller.org where folks have independently tested the methanol and isobutanol concentrations in collected distillate from pot distillation. Counter-intuitively, isobutanol (boiling point 226F) was concentrated in the heads/foreshots, while methanol (boiling point 148.5F) was concentrated in the tails. The chemistry involved is more complicated than meets the eye – the presence of water complicates the behavior of the alcohols during distillation.
The following graph illustrates the relative concentration of methanol and isobutanol to ethanol across 6 fractions collected from a pot still. It indicates that methanol is actually concentrated in the tails, not the heads or foreshots – and similarly, illustrates that isobutanol is concentrated in the heads, not the tails, as you might expect from a high-boiling point compound.
For more reading and graphs, see:
https://homedistiller.org/forum/viewtopic.php?t=79718
https://homedistiller.org/forum/viewtopic.php?f=33&t=40606
We hope this article clarifies common misconceptions about methanol and distillation. To recap:
In a typical fermented mash, components such as methanol and ethanol do not boil off separately at their individual boiling points.
Instead, the mixture has its own boiling point, and all components begin to evaporate together once this temperature is reached.
This means that methanol cannot be selectively removed by discarding early distillate fractions. We can go a step further and state that in a pot still, you’d actually be more effective at reducing methanol by discarding late fractions (tails).
Therefore, distillers should focus on making cuts based on flavor profiles or economic reasons rather than attempting to eliminate methanol through cuts driven by temperature readings. Understanding the chemistry of miscible solutions is essential for producing high-quality spirits.
