StillBehindTheBench - 2020-05-29
Greetings all, This is my first video, Part 2 of 2, and it is about what happens to methanol when it is distilled. Audio might be a bit wonky, still working out the kinks of microphone placement. Thanks for watching! Part 1 - https://youtu.be/mN1YLRuw92E
So the esters and acetone are problematic, can you do a video regarding how those act while distilling spirits with both a pot still and a column still.
Acetone and any other ketones will largely leave at the beginning of distillation because they are very volatile and don't really bond with a lot. An imperceptible amount of acetone might stick around with methanol but it will still leave in the heads cuts. Wouldn't be worth making a video about ketones.
But esters on the other hand are what makes up most of the flavour compounds in the spirit you are making. They are both made and distilled out of the wash, during distillation. It's a very large group that don't all act the same. I do intend on making a flavour compound video though, and I will be talking a lot about esters in it.
Your Presentation goes into more detail than any other post regarding this that I’ve ever seen on Facebook or YouTube. Good job.
A few years ago I gave a bottle of rum to a teacher at uni, they said (later) that they wouldn’t even touch until they had put a sample through the mass spectrometer.
They said that there was around 10-12 ppm methanol, which they were happy with, as commercial spirits can have up to 100-130ppm methanol… is that true?
It can actually be much higher than that. Spirits based on stone-fruit (plums, peaches, cherries, apricots, etc), or on the skins (marc, grappa, orujo, etc) of fruit, usually have the highest concentrations. I've read studies where it is as high as 13000ppm (13000mg/L). It's because pectin, being a plant structural component, is going to be found in higher concentrations in the skins. As for stone fruit, I don't think they have a higher concentration of pectin, just that its structure is slightly different, and so it's more available to be extracted from the fruit.
For commercial products, there are legal limits though, based on the type of spirit you are making, and they are almost always well below the amount that would cause any noticeable health issues.
@StillBehindTheBench I thought so, thanks mate.
this is great! keep these videos up bro!!
Excellent. I learned something.
How is acetone formed in the still and where does it come from?
It's a semi-complex set of steps, but I'll condense it for you.
To put it simply, the yeast will produce Pyruvate via the glycolytic pathway like normal, as I talk about in the fermentation videos. But only under aerobic conditions does that pyruvate gets turned into Acetyl-CoA, under anaerobic conditions it goes on to become ethanol instead. Via a couple of intermediates, that Acetyl-CoA gets turned into Acetoacetate, and then Acetone. The creation of acetone, also seems to be for the purposes of producing some other compounds, so it is an intermediate itself. But if the oxygen runs out, than the creation of those other compounds never happens, and so you end up with acetone in your wash.
So in all cases, and there is like 3 different pathways it can take to produce acetone, that Pyruvate needs to be turned into Acetyl-CoA for acetone to be produced, and that only happens under aerobic (oxygen-present) conditions.
That is why so little acetone is produced in the first place, even in the heads. If you do smell acetone, while it is possible that you are actually smelling acetone, a more likely culprit is a high concentration of ethyl acetate, which can smell like acetone in high concentrations, whereas in low concentrations it has a fruity smell.
Hi Adam, so redistilling tails in a column still, will get the methanol right from the beginning out of the still. If we have a thermometer at the top of the column can we assume that when the temperature will rise above the boiling point of methanol we have most of the methanol out? As you said, at the top of the column initially we will have high concentrations of methanol so the boiling point of the mixture will be close to the boiling point of pure methanol or somehow below that, due to the azeotrope mixture with acetone
Canuck! That’s awesome, thanks for the clarification. You dumb this very good.
There is one thing i dont get. Methanol forms an hydrogen bond, Ethanol forms an azeotrope. Isnt this azeotrope bond stronger? If so, why can we distill ethanol from around 75C but would have a boiling point closer to water?
Both Methanol and Ethanol form a hydrogen bond, the Ethanol hydrogen bond is stronger though because it's further away from the methyl group, which would disrupt the hydrogen bond, that's why it forms an azeotrope and methanol does not.
The BP of pure ethanol is around 78.5C, but the BP of a water/ethanol mixture is actually lower, at 78.2C. Everything in that liquid mixture is already evaporating, just from the heat energy in the environment. If you poured the mix into the still, turned on just the condenser, and had a coolant with a temperature lower than room temperature, also putting the receiving vessel in something like an ice bath, you would find distillate from your wash in your vessel. It's why a glass of water on your countertop will evaporate throughout the day, and the volume of water will get smaller. That rate of evaporation will increase if you add more heat energy, which is why evaporation in a still increases as you add heat energy to the kettle/boiler. Evaporation is only a surface phenomenon though. This is also why certain compounds that have a BP higher than water, but are also insoluble in water and less dense than water, will come out earlier in the distillation process. They evaporate away, since they are floating on the surface of the wash.
Boiling on the other hand is where you have increased the temperature of the liquid enough that the pressure the liquid is exerting outwards on the atmosphere, is higher than the pressure of the atmosphere pushing inwards on it, so it turns into a gas, and travels up the still.
Brilliant Videos mate
Jock - 2020-09-18
Great stuff, I’ve been distilling for years and am still learning. Cheers 👍🏻