ABV dependent volatility of fusel oils

[Edwin Croissant]

On first sight one would expect that methanol with its lower boiling point would concentrate in the heads and that isoamyl alcohol with its boiling point of 130 degrees Celcius would not show up in the distillate at all. Reality is not that simple. The volatility of fusel oils and methanol in a water-ethanol mixture are dependent on the ethanol concentration (ABV) as reflected in the following graph:

For methanol this means that, contrary common believe, methanol is released rather late in the distillation process and isoamyl alcohol (sharp and burning odor) is carried over rather early during a simple distillation and spread out over the distillate during a second distillation:

It looks to me that making a neutral with a pot still means making cuts in the stripping run. (Isoamyl concentration is shown in ml/100ml pure alcohol and in mg/l distillate )

When a packed column or a column with many plates is used, the fusel oils concentrate in that region of the column where the volatility is the same as the ethanol water mixture and will therefore not reach the top of the column as shown in the following drawing:

While searching the internet I found two things in relation to fusel oils that might be of interest:

When distilling is done with a packed column the fusel oils do not reach the top of the column and remain therefore in the boiler after the run. In some recipes, part of the backset is recycled to form the base of the next wash. Fusel oils are according to the article Fusel Oil Recycle—A Silent, Odorous Killer 10 to 15 times more toxic to yeast then ethanol. Maybe this is the reason that the fermentation process stalls after many generations. The fusel oils can perhaps be removed at the end of the distillation run by going from fractional distillation mode to pot still mode.

When the fusel oils are not removed in a column, the fusel oils concentration will rise to a level that demixing take place. This instantly lowers the boiling point of the ethanol-water mixture, causing a uncontrolled evaporation which forces the fusel oils out of the top and bottom of the column. The heat required for the evaporation is retrieved from the supplied vapor and the resulting condensation result in flooding. After the hiccup the column stabilize again until the next disruption (fusel oils induced column hiccups). It seems to me that the more liquid the column contains the more fusel oils can be tolerated, the least sensitive a column is for these hiccups. A column with plates or a packed column with a bubble ball or torpedo underneath should be therefore be more stable to run.

Happy distilling,

Edwin

[steve2md]

Sweet. I dig it when science happens! But then again, I'm a bit anal about this hobby (I'd collect in thimbles to do more accurate cuts if it were feasible)

[Odin]

Hi Edwin,

I see the higher boiling points build up especially to be a problem in a continuous distillation system.

Odin.

[Usge]

Maybe I'm missing something here. I'm looking at your first graph and your assumption that the ethanol and methanol concentration is increasing throughout the run. However, that's not how the distillation cycle works.

I think you are reading your first chart backwards. Ethanol abv does not increase through a simple distillation cycle to the end. It falls.

In terms of a separate rectifying column....what takes place inside the "pot" that feeds that column it's vapor is still the same (ie., the proof drops through the run). The rectifying column takes the vapor from the pot and rectifies it to higher purity as it goes. So, the pot would be feeding vapor to the column that contained less and less concentration of methanol.

As far as backmashing, that's normally only done on runs of "wash"...not spirit runs. And what is recycled on a spirit run is what has already been distilled...not what's left in the pot after such a run.

[shadylane]

I came, I read, I studied, now I'm fumbuzzled.

[just sayin]

Edwin,

Great research, even if you have kicked the foundation from under what I thought I knew. I am going to have to revisit your graphs in the morning with a little clearer head. Thanks much for your post; you are helping push forward the frontier of our collective knowledge.......................Just Sayin'

[Edwin Croissant]

Usge, the topic is not about methanol and the graph is not about methanol en ethanol concentration. It is about fusel oils, isoamyl acohol, butanol, propanol, etc., the higher alcohols so to speak, and the way they distribute over the distillate in relation to the strenght of the mash. With a low strength mash they concetrate in the heads, with a high strength wash (the result of several stripping runs) they are more spread out over the distillate.

just sayin, yes it knocked out the foundation of what I thought to. Surprisingly this behavior is known for more then a century. In “Distillation principles and processes” by Sydney Young, published in 1922, the relative volatility of isoamyl alcohol is addressed together with the way to handle this in continuous distillation. References are made in this book to publications from 1891. I found one referenced book “La rectification de l'alcool” by Sobel and first published in 1894 which shows the same kind of diagram how the fusel oils concentrate in the column: [td][attachment=0]Sorel.png[/attachment][/td][td][size=85]But there are bodies such as amyl alcohol, for which the value of K is significantly smaller than unity in the presence of concentrated alcohol, while it becomes significantly larger as the alcohol is diluted. These bodies therefore behave according to the diagram Fig. 2 in the upper part of the column and according to diagram of Fig. 1 in the lower part. The result is that from the top down to the lower trays they tend to accumulate in a specified area of the column, and the level of these impurities can be represented by the diagram represented in Fig. 3. These body accumulate in a series of plates in the column, this is the region they stay, not the boiler, and this is the danger zone, only the portion of the column situated above this area is actually useful for rectification.[/size][/td][td][size=85]Mais il existe des corps, comme l'alcool amylique, pour lesquels la valeur de K est notablement plus petite que l'unite en presence d'alcool concentre, tandis qu'elle devient notablement plus grande, des que l'alcool commence a etre etendu. Ces corps se comportent donc suivant le diagramme de la fig. 2 dans la partie superieure de la colonne, suivant le diagramme de la fig. 1 dans la partie inferieure. Il en resulte que ramenes de haut en bas dans les plateaux inferieurs ils tendent a s'accumuler dans une region determinee de la colonne, et que le taux de ces impuretes peut etre represente par le diagramme represente par la fig. 3. Ces corps s'accumulant dans une serie de plateaux de la colonne, c'est la partie occupee par eux, et non la chaudiere, qui constitue la zone dangereuse, et il n'y a que la portion de la colonne situee au-dessus de cette zone qui soit reellement utile pour la rectification.[/size][/td] I hope that my translation is not to far of what Sorel meant. I humbly admit that the 5 years they tried to teach me French was a completely waste of time for all parties involved

Odin, I am not sure if the build up of fusel oils is only a problem with a continuous still. Sorel spend most of his book on discontinuous distillation, only the last chapter is dedicated to continuous distillation (regretfully there is no English translation of this book). Yet he wrote about the danger zone... In the data I used the concentration of the wash is 146 mg/l. A 35 liter boiler contains therefore about 5 grams of isoamyl alcohol. 90% is carried over in the distillate. That's about nearly 6 ml concentrating in the column. With a wash with a concentration of 502 mg/l this result in nearly 20 ml concentrating in the column. That is 1 cm of fluid in a 5 cm column. It is not concentrating in one small layer but is is not concentrating as a fluid either, part of it is vapor. One solution I found for this type of problem in a waste water plant with a methanol rectifier with hiccups was to lower the distillate concentration so that just enough of the trouble causing substance was carried over in the distillate to keep the concentration in a safe region. I wonder if reducing the power make it possible for these fusel oils to flow back into the boiler at a rate just enough to keep the concentration in a safe region and that all that flooding that take place is mostly caused by fusel oils buildup.

I start to like the idea of a hybrid column with a couple of deep plates to start with and a packed column on top.

Edwin

[Usge]

I wont' rehash the argument/disagreement/discussion over methanol. But, your first chart clearly has a methanol curve on it along with the other fusel alcs. And it clearly shows it going "up" with increasing ethanol concentrations. And just under that chart...you refer to it as well (methanol) and suggest that contrary to popular belief...that this chart shows it is released later in the run (during decreasing abv). The chart doesn't show that. It shows decreasing concentrations at lower abv....ie., later in the run. I won't mention that ethanol is not a constant either during distillation...nor is the mixture in your pot which is continually changing as ethanol and other compounds are extracted during distillation.

I seem to recall several discussions here and elsewhere on proofing the still charge if thats what you mean by "high strength wash...etc. vs low strength mash". As well as discussions on soluability issues with ethanol and other compounds. It sounds to me as if that's more on the lines of what you are trying to get at (soluability issues with ethanol and other volatiles).

Lastly, congeners are very important to making good whiskey and brandy. The only reason you'd want to minimize them or severely restrict them might be if you were making vodka or going for something as tasteless and odor less as possible. I personally have never had oily, cloudy heads full of fusels. And the only reason I can think that might happen would be in a continuous process...or if you didn't rinse/flush the still well enough before finishing a previous run before starting a new one.

[Prairiepiss]

Ok so I'm cornfused. Most of what you are pointing out. Is about continuous distilling process. Not batch stillin process. Which as far as when each fraction is released. Is very different.

So are we talking about continuous distilling or batch distilling in this thread? Continuous distilling isn't generally discussed around here. As it isn't really a feasible option for a hobby distiller.

And if this thread isn't about methanol. You sure led it off with a bunch of methanol information?

[Edwin Croissant]

The book “La rectification de l'alcool” by Ernet Sorel contains a chapter called “Improvements of a discontinuous rectifier” in which I found this piece of text (I hope that my translation (thanks to google translate) reflects the meaning of the french text):

Show Spoiler

[td]En reprenant l'idée de l’extraction, appliquée par Amand Savalle à son rectificateur continu en 1857, le directeur actuel de la maison Savalle a établi une prise spéciale au quart environ de la colonne, où se concentrent les corps de queue à la fin de la période des bons goûts. En retirant une faible quantité d’alcool dans cette zone, on extrait une proportion de corps de queue très considérable, le taux de ces corps dans la zone dangereuse ne peut plus augmenter, et l’on arrive ainsi à prolonger la période des bons goûts, par suite à augmenter le rendement de l’appareil sans augmentation de dépenses. La théorie, d’accord avec l’expérience, a montré que la zone d’infection maxima se trouve au-dessous des plateaux contenant de l’alcool bouillant entre 80 et 81°. Il suffit donc de maintenir le plateau où se fait l’extraction dans ces limites de température, et dès lors la zone d’infection ne pourra plus s’élever vers les étages supérieurs. On y parvient aisément par l’emploi d’un condenseur intermédiaire placé au-dessus de la tubulure d’extraction et dont on règle l’alimentation de façon qu’un thermomètre placé dans le compartiment immédiatement supérieur accuse la température voulue. Cette addition n’entraîne que très peu de dépense de combustible, car le condenseur n’a à fonctionner que vers la fin de l’opération.[/td][td]Returning to the idea of extraction, implemented by Amand Savalle to the continuous rectifier in 1857, the current director of the house Savalle has established a special socket at about a quarter of the column, where the concentrated body tail end the period of good taste. By removing a small amount of alcohol in this area, a proportion of very considerable body tail is extracted, the rate of the body in the danger zone can not increase, and one arrives to extend the period of good taste, owing to increase the performance of the device without increasing spending. The theory agrees with the experiment which showed that the maximum area of infection is below the trays containing alcohol boiling between 80 and 81 °. It suffices to keep the plate where the extraction is in these temperature limits so the area of infection can no longer rise to the upper plates. This is readily accomplished by use of an intermediate condenser located above the extraction pipe and the power of which is adjusted so that a thermometer placed in the next higher compartment acknowledges the desired temperature. This addition result in little or no spending of fuel as the condenser has to work only towards the end of the operation.[/td]

I think that when in the early 1800's continuous stills were put into operation the operators experienced fouling in a certain region of the rectifier. In 1857 the still builder Amand Savalle (formally a Dutch sugar-trader ?) implemented a take-of point in the rectifier to drain the bad tasting alcohols that fouled the rectifier. A director of the house Savalle applied that solution to a discontinuous still by installing a take-off point at about a quarter of the column and to prevent the fusel oils infected area to rise up into the column when the charge of the boiler is depleted, he installed a condenser just above the take-of point to keep the temperature in that region around 80 to 81 degrees Celcius (65 to 75 % ABV). This increased the performance of the still and, as the condenser only had to work at the end of the distillation cycle, without using to much fuel.

The use of SPP and lava-rock as packing material increases the efficiency of a still and I find it plausible that fusel oils build-up will become (if not already is) a problem. I think it is good to know that more then a century ago a solution was found

[Odin]

He clearly states: a continuous rectifier. And yes in a continuous still, I see this happening. Not in a discontinuous system. It does not have just one opening above the middle, as a continuous still, but two. One close to the top, another one at the bottom (where column meets boiler) ...

I think that in a continuous system without drain at the bottom or at the top, there would not only be a problem with higher bp alcs, but also with headsy factions, becoming ever more intense and bleeding into hearts ...

Odin.

[Usge]

So, tell me again...what is it that we are changing in regards to commonly held beliefs around here...where we do batch distilling at home...as a result of Edwin's assumptions based on these charts that have to do with continuous still column contamination?

Not trying to be a dick. It's just this is the 2nd time Edwin has started a thread here that was prefaced with "undoing" conventional wisdom and the way things are taught and done around here. And while certainly some of the subject matter is interesting no doubt...and may have some crossover in certain areas...I think it does more a disservice to less experienced members...and to this forum as a whole ...and to the mentors of this forum...to come in here with 19 posts, no distilling experience...and seek to change the basic common understanding that we have here for what we do here by using charts out of context and presenting them in a way that could easily be misleading...if not outright confusing with mixed up terminology, etc. that I've been here long enough to know is not from any translation/lang issue but from a lack of fundamental understanding of the terminology and what it means.

This place is certainly open for discussion! So, I'm not trying to suggest you not talk about any questions you might have...or bring up things you want to discuss within the realm of what we do around here. But, I can tell you...as a mentor on break...that its extremely tiring and takes up a lot of time that could otherwise be used to help people....when we have to spend our time addressing misunderstandings or out of context material, or misinformation presented as a challenge to disprove or defend what we already know/understand. While certainly, there is some element of that in any research and theory discussion.... The 20 people who read it and get confused or misunderstand it...turns into 20 more...and they get even less of it...and the wrong information starts make it's way through the internet like a 3rd gen passed on recipe for "mash" that each who passed it on added their own misunderstanding and misinterpretations to....who come here and and instead of wanting to first learn what we know (collectively)..ie., how to make a proper mash and what that means....decide to proceed to challenge us with their F'd up recipe to explain to them why it didn't work. Speaking for myself...it gets old. And its tiring.

That obviously isn't all directly aimed at your Edwin. I appreciate very much your zeal and wanting to dig into the deeper more analytical/theory side of things. And I certainly don't want to discourage you from that. I'm just suggesting you might want to walk a little more before you run...and maybe try and present what your looking to discuss a little differently.

No hard feelings. Just speaking my mind. And again...I'm speaking generally about the site (not "for" them) ...these are just my personal opinions. So, any objections or etc...aim them at me...not homedistiller or it's staff of mentors, moderators and admins.

[Prairiepiss]

+1 Usge. What is the point of this thread. And where does it fit in with home distilling with batch ran systems?

[Edwin Croissant]

I have thrown the cat among the pigeons. I shattered a little part of your conventional wisdom and what is taught around here. And that leaves you worried. And because you cannot refute the message (knowledge that is discovered for more then a century ago) you attack the way the messenger is presenting his message with fallacies.

I strongly believe that knowing what is when carried over under which conditions can help a keen man making a better product and a better fractional still.

It may be exaggerated, or maybe not: consider the man who make bio-diesel and inadvertently throws the leftover methanol from that process into the jar he uses to recycle his heads and tails. Never mind he thinks, this nasty stuff ends up in the fores anyway he have learned here. A mistake he probably can not repeat.

The knowledge is there, you only have to detach from your cherished theories and be open to new (or in this case a century old) information.

Edwin

[Usge]

While you are throwing your cat among our pigeons to carry our homedistilling to another level with your centuries old knowledge....perhaps you could do us all a favor and at least learn the difference between a wash, mash and low-wines? That would be a start. And helpful.

[Prairiepiss]

I have thrown the cat among the pigeons. I shattered a little part of your conventional wisdom and what is taught around here. And that leaves you worried.

I'm not worried about crap. I'm just trying to figure out how this information. That is geared mainly towards continuous distillation. Fits into the big picture of hobby scale batch distilling? We have asked a few questions. And all you post is something about your cat. And more quotes from the book. So if you yourself could tell us what this all means for a hobby distiller. Using a batch still reflux or pot still? I for one can't seem to find the relevance. So I need to be pointed in the right direction.

[rad14701]

I'd have to do a bit more research before adding anything to this discussion... I have a good idea what the crux of this is but want to make sure before stating anything right now... But first I'm going to reread the topic from the start...

Let's throttle it back a little here and keep minds open... True, this is nothing new and may not fit into our common distillation practices but, then again, there may be something...

[pizzaninja]

okay with and post 6 of this thread I decided to make this comment. seems to be a easy fix. say if you have a 6 plate column. instead of your third plate returning just to the downcomer and your second plate return it directly to the boiler. Making it in essence a two ply system. Or beter yet half and half half back to plate 2 half to boiler in order to do this vapor speed in the column would have to be greatly understood. if you have sight glasses throughout each bubble plate this would be easily obtained. I have seen a design with flow from each plate back to boiler but to solve this I say it would work fine from plat 3 at a 50/50 ratio. Ok feedback welcome let's make some new shit possible........

[Edwin Croissant]

Distilling, as I understand, is separating the good stuff from the bad stuff. Part of the bad stuff is fusel oil. The volatility of fusel oil is depending of the ethanol concentration. So what does this relative volatility mean for homedistillers?

For pot still distillers it will make a difference if cuts are made during the first distillation. Isoamyl alcohol for example will mainly be carries over in the heads when the mash is diluted to 5%, because Isoamyl alcohol is at that strength much more volatile then ethanol. When low wines are distilled, Isoamyl alcohol is carried over deep into the hearts, as at 32% ABV it has the same volatility as ethanol. So making your cuts in the first or second distillation (or both) will have an different influence on taste and quality.

As Isoamyl alcohol is less volatile then ethanol above 32% ABV things get interesting for distillers who use a column. This fusel oil is trapped in the lower part of the column until the still is depleted, then the fusel oil climes up into the column and is eventually carried over in the tails.

How much fusel oil accumulate in the column is depending of the rate it enters and of the rate it leaves the column. When the distillate is below 80% ABV, the fusel oil is carried over in the distillate and normally no accumulation takes place. Above 80% ABV, the fusel oil accumulate until the supply and drain (at the top and at the bottom of the column) are in equilibrium. If no equilibrium is reach the fusel oil will eventually demix and flooding will occur.

Fusel oil trapping in the column is a good candidate for the cause of flooding in combination with fractional distillation of low wines, as there is a 3 to 4 times higher fusel oil concentration (as nearly all the fusel oils are carried over in a stripping run), combined with 30% less reflux. The stable operation distillers are reporting about their column on top of a bubbleball, can probably be credited to the extra volume available for the fusel oil.

Another approach is to bleed of the fusel oil during distillation and I found on the forum homedistiller.ru a post from morfiy (post #28 second page) who did that with a take-off in the lower part of his column. He writes that he opened the valve shortly for two seconds to bleed off 5 ml of fluid and 2 ml of vapor every 15 minutes and that the liquid stinks terribly.

I think that with simple means, there is room for improvement.

Happy distilling,

Edwin

[dullfig]

suppose you had a continuous still; if you bled off some liquid near the bottom of the still, and drained that into the reboiler, would that solve your problem? seems this would recover a little bit of your ethanol that might otherwise be wasted.

[Edwin Croissant]

All the continuous stills I have seen take the fusel oil out of the system. Leaving the fusel oil in the system gives a lot of problems. I have seen several patents about how to recover the ethanol from the side stream. Cooling and decanting seems to be the trick. Fusel oil has it's value, I have seen prices of about 2000 USD per ton.

[dullfig]

what book is figure 3 from?

[Edwin Croissant]

what book is figure 3 from?

From a publication of the International Centre for Brewing and Distillation called Unit 5 Continuous distillation

[dullfig]

Ok, so the fusel oils accumulate towards the bottom of the rectifying column, until it becomes too much and the still "burps". Any idea what the specific gravity of the mixture would be right before burping? what if you kept checking the gravity with a hydrometer, and kept it under a certain value? would that tell you when to draw some liquid?

Dan

[Edwin Croissant]

Ok, so the fusel oils accumulate towards the bottom of the rectifying column, until it becomes too much and the still "burps". Any idea what the specific gravity of the mixture would be right before burping? what if you kept checking the gravity with a hydrometer, and kept it under a certain value? would that tell you when to draw some liquid?

Specific gravity of of the various alcohol do not differ very much. I found mentioned in Fusel oil: Composition, removal and potential utilization by Patil, Koolwas and Butala. (The filename is FUSEL-OILpaper.pdf and google is your friend) that a novel control scheme, which utilizes differences in temperatures between bottom temperature and average temperature of fusel oil zone, was found to be very effective.

I haven't found a real number on how much to draw of and iirc the fusel oil concentration should be kept under 3%. So just to suck something out of my thumb suppose the concentration of fusel oil in the vapor is 0,3% you will have to bleed 10% off your vapor rate to limit the concentration to 3% to balance the supply and take-off.

Maybe you can find more information in the technical papers from Hermino M. Brau.
Technical paper 17 Review on the origin and composition of fusel oil (April 1957)
Technical paper 18 Automatic controls in continuous alcoholic distillation. (April 1957)
Technical paper 24 Fusel oil in alcoholic distillation: experimental data on its distribution by plates of continuous distillation columns under different operating conditions. (January, 1958)

Edit: thump --> thumb
To suck out of one's thumb is Dunglish for implying that an answer was just a wild guess or the notion had no evidence. The same expression is used in Russian, Hebrew and Afrikaans.

[dullfig]

I read something interesting in a Google book; the book is called "Whisky: Technology, Production and Marketing" by Inge Russel. Grain whiskey is produced in continuous stills. In order to control the flavor profile of the alcohol, they have three separate extraction points for the fusel oil, corresponding to the three bulges in figure 3, so they can adjust how much of the different components carries over with the ethanol. Of course this would be a huge complication on a hobby still; I just found it interesting.

[buflowing]

Thanks for the insight Edwin. I always do what I think is a liberal fores cut on my pot still strip runs. I'll be paying more attention to my fores/heads collection on my next strip runs to see what I can distinguish. I am unaware of isoamyl alcohol characteristics and what it contributes to my whiskies. Any chance that's some of the stuff floating on top of my very late tails collection?

[rizzotherat]

Hi All,

I'm new to the forum but have been lurking for some time. I'm a pro brewer but new to distilling.
I've just started studying distilling (IBD) and have been reading this thread with interest.

I've I could sum up what we are talking about and I'll had a little of what my notes say on the topic I think may help the generally understanding. Please step if I what I say is confusing or incorrect. I'm still learning.

Methanol IS more volatile than ethanol. IE: it will come off with the heads along with acetaldehyde and diacetyl

IF methanol is still present is a higher alcohol concentrate solution it becomes MORE volatile. But only slightly so.

Fusel oils (mainly iso-amyl alcohol) concentrate in higher alcohol strength fractions (65 to 70% for iso-amyl, 75% to 80% for propanol & iso-butanol)

Fusel oil is removed by collecting the appropriate alcohol concentration fraction in a decanter, mixing with cool water (therefore lowering the alcohol strength) which separates the oil that floats to the top of the vessel, which can then be decanted off.

Keep in mind that the removal of fusel oils is usually in the quest for Neutral Spirit. If you are seeking some flavour from you base ferment some fusels are desirable.
If you are getting comments that your liquor is 'hot' or 'solvent like' you may wish to look closer at your wash ferment temp and the yeast that you are using to control that amount of fusels that are created initially.

I hope this helps and I look forward to learning a lot more.

Cheers,
Rizzo.

[Edwin Croissant]

Thanks for the insight Edwin. I always do what I think is a liberal fores cut on my pot still strip runs. I'll be paying more attention to my fores/heads collection on my next strip runs to see what I can distinguish. I am unaware of isoamyl alcohol characteristics and what it contributes to my whiskies. Any chance that's some of the stuff floating on top of my very late tails collection?

You are welcome During my limited research I have not come across a clear answer if the vintage distillers made cuts during the stripping run or a low wine run. I may have overlooked, I may have missed the book that explains it all, but I wonder if this was not a closely kept secret. It is not in the best interest of a distiller who makes a perfect cognac, jenever or gin, to have his successful method published. Making cut during a stripping run will make a distinct difference as the fusel oil will be more concentrated in the first part of the run. Agitating might concentrate them even more.
My goal at this moment is to understand the distilling process and I am at this moment not researching what the influence of the fusel oil is on the taste so I can't be of any help here.

Methanol IS more volatile than ethanol. IE: it will come off with the heads along with acetaldehyde and diacetyl

IF methanol is still present is a higher alcohol concentrate solution it becomes MORE volatile. But only slightly so.

I'm afraid that methanol is at low ABV concentrations less volatility then ethanol. At a mole fraction of 0.05 (± 15% ABV) the k factor of methanol is about 6 and k factor of ethanol is about 10. At a mole fraction of 0.8 (± 94% ABV) the k factor of methanol is about 1.6 and k factor of ethanol is about 1. With a simple distillation it will not come out in the fores and will actually concentrate in the tails. When you have a still with a column and you let this still in full reflux for a very long time eventually the methanol in the boiler will concentrate in the top of the column. This explains the first peak you see in the graphs how methanol is spread out of the distillate during a run of a still with a column.

Fusel oils (mainly iso-amyl alcohol) concentrate in higher alcohol strength fractions (65 to 70% for iso-amyl, 75% to 80% for propanol & iso-butanol)

Do you mean the fusel oil concentration in fractions of a pot still run or how the fusel oil concentrates at the various levels in a rectifying column?

[rizzotherat]

Methanol - top of the column. Gotcha.

Fusels - I believe the notes were referring to how the fusel oils concentrate at various levels of the rectifying column. This is why a lot of neutral spirit stills have a facility to collect at these plates.

Cheers.