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Comment by akersten | Hacker News Reader

> This is actually a myth. I’ll have to see if I can find the papers I read but mass spectrometry has shown that methanol comes out throughout the entire process. The idea that things come out at their boiling temperature is a drastic oversimplification.

Please do find those papers! They may be describing a radical new chemistry that I'm not familiar with.

To be clear - methanol boils at 64C and ethanol boils at 78C. Are you suggesting that in standard distillation, there is still some non-trace methanol coming over at 78C? If I personally observed that in a laboratory setting, I'd quickly assume measurement error or external contamination.

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I suspect that the vapor of the mash is always a mix of the components, and even above the boiling point of methanol, it still produces a mixed vapor. At room temperature, all of the components produce some vapor and will evaporate. This continues as the temperature rises.

It's not clear to me that simple distillation of a methanol/ethanol mixture can produce either pure ethanol or pure methanol at any point, just as it's impossible to distill ethanol and water to pure ethanol (absolute alcohol) if the water is above a small percentage of the mixture.

Yup, distillation never produces a pure product. Cask-strength whiskeys contain quite a lot of water, even though nobody is stupid enough to distill at 100C. Even an industrial column still can't go over 96% ABV.

There is always some amount of vapor pressure, even below the boiling point of a substance. Otherwise, neither water nor alcohol would evaporate by themselves at room temperature! The temperature we call the "boiling point" is just the temperature at which the vapor pressure equals the ambient pressure.

You can't distill out pure methanol, as at the boiling point of methanol ethanol also has some vapor pressure, so you distill a mix. However above that boiling point you distilled out all methanol (with a mix of ethanol), and the remaining ethanol should be free from methanol.

This also matches what happens when distilling ethanol from water. You can't distill pure ethanol, but you csn distill ethanol-free water afterwards.

> above that boiling point you distilled out all methanol (with a mix of ethanol)

That's not what studies have shown. Methanol boils off in all phases of distillation, and remains in high concentration at least halfway through.

https://pubs.acs.org/doi/10.1021/acsfoodscitech.3c00627

https://pubs.acs.org/doi/10.1021/acsfoodscitech.1c00025

Thank you for finding these! I remembered they existed but not where

"This also matches what happens when distilling ethanol from water."

Right, normal commercial ethanol production is 95% EtOH, 5% H2O (the constant boiling mixture/azeotrope). That's good enough for most uses but not all. The only problem the average person would ever likely encounter from the residual H2O would be in the application of alcohol-based coatings such as shellac where it can cause whitish discoloration. Painters will occasionally use 99% EtOH which is substantially more expensive (removing that residual H2O requires an altogether different proxess).

>To be clear - methanol boils at 64C and ethanol boils at 78C. Are you suggesting that in standard distillation, there is still some non-trace methanol coming over at 78C?

From what I remember, the highest concentration of methanol is in the tails. That should tell you everything.

*EDIT* Found the paper

https://op.europa.eu/en/publication-detail/-/publication/0b9...

There are azeotropes - mixtures that distill together at a different temperature than either alone.

You can’t distill ethanol to higher than 95% because of the 95-5 ethanol-water azeotrope that boils at 78.2C, versus ethanol alone at 78.4C.

Methanol-water and methanol-ethanol don’t form an azeotrope so if properly done you can separate methanol via distillation.

Yes. It doesnt work the way you think. When you mix chemicals together and then boil, the result isn’t that simple.

Think of it this way: ethanol boils at 78.5. Water at 100. But when I’m distilling, the first stuff out of the still is coming out at like 80/20 ethanol to water, long before I’m near 100C. The later stuff still has some ethanol in it, even as I near 100C. (You can easily measure while distilling.)

So why would it be surprising that methanol behaved that way as well?

When you mix different liquids, all manner of complex things happen to their vapor pressure vs temperature curves.

https://en.wikipedia.org/wiki/Brownian_motion

Temperature is just an average, the individual molecules can have a higher or lower temperature and can therefore evaporate already below boiling point.

>They may be describing a radical new chemistry that I'm not familiar with.

It's probably pot still vs. reflux still. Chemists use fractionating columns to get better separation. Home distillers won't necessarily do so, so official advice has to assume they will not.

Yeah column stills exist for home use but they’re not very popular. They’re big and expensive and strip flavor. It’s probably because Home distilling, like home brewing, is largely focused on the craft side rather than trying to get drunk cheaply.

If you’re trying to get drunk cheaply, and without tasting liquor, you cannot beat the product and efficiency of a column still.

But I want my whiskey or apple brandy to have the characteristics of the mash I distill it from. A column still would reduce that.

So most home distilling is a pot still for sure.

We could be breaking new grounds with spinning band distilled moonshine.

I mean—depending how much methanol was in the mix to begin with…

It’s been a long time, but I thought there was a whole Raoult’s Law thing, about partial pressures in the vapor coming off the solution combining in proportion to each component’s molar fraction * its equilibrium vapor pressure (at that temperature, presumably). Or something.

Point being, if you’re starting with a bunch of volatiles in solution, there’d be quite a bit of smearing between fractions boiling off at any given temperature/pressure. And you’d be very unlikely to get clean fractions from a single distillation anywhere in that couple-dozen-degree range.

Probably mangled the description, but isn’t that why people do reflux columns?

I would assume it depends on what you are distilling.

If you are making brandy from clarified wine, it probably separates better than rotten grape mash.

It is still a continuum with some methanol molecules likely remaining even in the tails.

For all intents and purposes, the distiller's rule of thumb of throwing away the angels' share is still going to work because low methanol concentrations are never an issue —for the antidote for methanol is ethanol.

You throw away the foreshots because they also contain things like acetone that taste bad and may be harmful. They’re highly unpalatable so people can be relied on to do a sufficient job.

Also “Angel’s share” isn’t what you throw away, it’s what evaporates from the barrel when you age. What you throw away are the foreshots and parts of the heads and tails

I had learned it like that(it could have been a different cute term) but the terminology I used does appear to be wrong afaict.

From what I understood ethanol and methanol form an azeotrope and boil together at a mixed temperature. And the going blind stuff is just prohibition propaganda both to make home distilled alcohol seem dangerous and to scapegoat the fact that the government was actively poisoning "industrial" ethanol.

this is dangerously wrong in several dimensions

methanol and ethanol do not form an azeotrope with each other, they only (both, each) bind to water. that's why separation of methanol and ethanol by holding key temperatures works at all.

furthermore, the azeotrope effect only becomes relevant at concentrations beyond 90% alcohol. so when you're producing pure methanol and ethanol, then distillation won't cut it beyond 90+% as water+(m)ethanol then *at these high concentrations* boil and evaporate together. that's the grain of truth in your statement.

last not least going blind from methanol is _very_ real.

Methanol will certainly make you go blind if you consume it at too high a ratio, it just isn’t a risk when distilling because you can’t feasibly make that happen on accident and it would be hard to even do it on purpose. I think that’s what parent likely meant.

> From what I understood ethanol and methanol form an azeotrope

I don't think so https://en.wikipedia.org/wiki/Azeotrope_tables

Look at it this way: The boiling point of ammonia is -33 C. Would you drink a jug of household cleaning ammonia just because it's been heated to +20C?

But anyway, I don't think there's hazardous levels left after normal distillation+cutting, the reason for not buying booze from some guy behind a barn usually has more to do with lead contamination risks.

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