Pot Still Vapor Temperature

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Pot Still Vapor Temperature

Post by ParrotHead » Fri Jul 24, 2020 11:57 am

Hi Everyone,

Note: My thermometer is in Celcius and is located in the swan neck, 8 gallon alembic pot, running 5.5 gallon batches of wash. I have done a lot of research on the internet and read a lot of books. I am a scientist by training and have been fermenting everything and anything since I was still wet behind the ears. I know that most of you will tell me to not rely on vapor temp and ABV, and even ABV more than vapor temp. That's fine and I have nailed down the taste and smell thing for making cuts with making rum, not an issue, I get, I smell it, I make clean product based on nose alone. The variability I have run into is with apple brandy.

Let me back up . . . the one thing I find distracting in all of the literature is the agreement on the pot still vapor temperature of the head to hearts transition. I think the most reliable that I have read from many sources including Rick Morris's book, "The Joy of Home Distilling" is that clean hearts starts around 91 degrees C or anything below 80% ABV (Problem here is that I have never seen 80% ABV coming off my pot still unless its foreshots or strong heads). I also typically do not measure ABV until I know I'm into hearts and hook up my tubing and parrot.

Other online documents say that 87.8 degrees C (190 deg F) is where hearts begins. I have a new Bourbon making book that does all the keeper cuts starting at 83 deg C using a pot still ! Based on my pot still this would expose you to methanol and definitely a bad headache if not worse. Based on what I have seen thus far, 80-83 deg C is where heads really starts flowing. So WTF?

I have been making some really incredible apple brandy with fresh cider I made using the 91 deg C area to start smelling my cuts for blending heads-hearts. Not a problem. Beautiful stuff, clean like my rum. Then I ran out of cider from last harvest. I decided to use a leading brand of apple juice that I have used before to make really good cider to put on tap when I did not have apples, addition of malic acid to pH down to hard cider level (0.6%). I made a run that was cut around 91 deg C and it was beautiful and no issues. I wanted to start experimenting since I had this juice at my disposal for a decent price, same juice. I decided to start collecting my small samples of heads to hearts transition around 88 deg C as one source said you could do, instead of what I have been using (91 deg C). One thing I noticed was that heads did not start until 87 deg C, which is really high and I only collected 150 ml of foreshots because of this. I have read that some apple brandy's just don't have a lot of heads and I figured this was the case. On the flip side I have read that apple brandy is notorious for a lot of heads. I did the methanol flame test and yes there was some methanol in the foreshots but by the time I reached 100mls there was clean blue flame.

I did my cuts based on 35% dilution, aroma and taste. I found a boundary where I stopped smelling mild hints of acetone, and where the ethanol really began to pop like your going into hearts, around 88 deg C and really cleaned up by 89-90 deg C. By pop I mean that burst of burn on your nose that's clean and lovely with bananas and cherry aromas, not much apple. So I added this to my hearts blend to try and add flavor. I started smelling the end of hearts and tails coming on with grilled squash aromas around 45% ABV. I stopped short of that for the final blend.

The final product smelled absolutely amazing and tasted amazing . . . until I started noticing a mild headache the next day and when I had a few two finger sifters the next night I found it difficult to sleep and was up at 3am with some anxiety and a cerebral, front of head balloon feeling, just felt spacey weird and had to drink a home brew to chill me back to sleep.

I've been reading and have noticed by experience that apple brandy can be difficult to determine aroma of cuts. Could this be what I was experiencing and picked up some funky funk on the weak heads cuts? I plan to re-distill it and start smelling cuts at 91 deg to see if it goes away.

Any experiences in this field are welcome on all fronts. I'm reading a lot and I'm learning a lot, and this post was thought out and I even hesitated but at this point I have read so much that I am now confused. LOL Thanks!

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Re: Pot Still Vapor Temperature

Post by NZChris » Fri Jul 24, 2020 12:57 pm

When distillers spit out temperatures, those temperatures are for their stills, run their way, with the thermometer positioned wherever they, or the manufacturer, put them. If you want to use temperatures, record everything relevant in your distilling notes so that you can refer to them in the future. Meanwhile, make your cuts using your senses and don't try to cut on the fly until you have enough history to refer to to enable you to do that. Personally, I find the vapor temperature too unreliable to be useful, so use the temperature of the charge.

Check your selection by making up a prospective blend before committing everything to their respective jars, then add to it from each end. You may find that adding from nasty jars at each end improves the flavor of the heart cut.

Apples ain't rum and have to be cut differently. Some of the VOCs (volatile organic compounds) you want for apple flavor come over very early. If your product gives you headaches, you might be better off making something else. I get a headache drinking some commercial hard ciders, so I just refuse to drink them.

Apple is higher in methanol than rum right through the whole distillation and the ability to remove methanol in a foreshot is a myth, not backed up by lab results.
viewtopic.php?f=33&t=40606
viewtopic.php?f=33&t=77481
Edited to fix link
Last edited by NZChris on Fri Jul 24, 2020 10:51 pm, edited 1 time in total.

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Re: Pot Still Vapor Temperature

Post by jonnys_spirit » Fri Jul 24, 2020 12:59 pm

Hi, You can't determine your cuts based on temp. Please do yourself a flavor and forget what you've read elsewhere for a while and please be willing to learn a little (or a lot depending....). Too many variable parameters in the fruit you used, your yeast, your fermentation parameters, your strip/spirit run protocols (you didn't mention doing a stripping run), and how you fraction out (separate) and choose your cuts (blend) - Plus airing and aging. Boiling cuts down to temp isn't helpful because "it depends".

Flame test is also pretty useless and dangerous around a still producing high ABV ethanol vapor potentially mixed with oxygen and/or jars of fractions laying about. Here's Yummyrum's flame test thread which is quite illuminating - viewtopic.php?f=1&t=75486

Here's kiwistiller's Novice Guide for Cuts (Pot Still) - viewtopic.php?f=63&t=13261

Also - Cranky's Spoonfeading thread - viewtopic.php?f=15&t=52975

These are all required reading please and will only help you.

There's some really good and detailed info around here on apple brandy if you would like use the HD Google Search function (towards the upper right corner where it shows "Google Search..."

Others may have different helpful suggestions as well.

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Re: Pot Still Vapor Temperature

Post by Saltbush Bill » Fri Jul 24, 2020 1:43 pm

Seems to me that your post is a classic example of why people are told not to try to run and make cuts by temperature.
Your nose seems to be working just fine.......your eyes and the thermometer are confusing you.

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Re: Pot Still Vapor Temperature

Post by LWTCS » Fri Jul 24, 2020 1:56 pm

100% what the guys have already mentioned.
If you must, pic a bench mark temp (because you seem data driven?) And work toward either direction to help dail in your point of view.
Truthfully, it just sounds like you need (dozens?) more runs under your belt.
Just pretend you are blind (or in the cover of night) and have to rely on your own good senses to conclude what's what.
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Re: Pot Still Vapor Temperature

Post by kimbodious » Fri Jul 24, 2020 2:24 pm

Forget about watching a thermometer. Collect in small amounts in sequentially labeled jars. Let the product rest and air in the jars for 48 hours before determining which jars go in your final blend. If in doubt leave it out (of your final blend).

Manage the heating power to your boiler so you are just at the earliest point of an unfaltering stream of output, what I refer to as low and slow. Some people even run their still as low and slow that they are only getting two drops of output per second. If you run your still low and slow it will make it so much easier in two days time to detect the differences between the jars.

This hobby rewards patience and care. If you are pushed for time leave your still run for another day!
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Re: Pot Still Vapor Temperature

Post by ParrotHead » Fri Jul 24, 2020 8:23 pm

You guys are awesome. Maybe I just needed someone to tell me to stop listening to all the temperature folks writing the books. But I do think that around 90 deg C is a good marker for me to take cuts for heads-hearts transition. I can drink hard cider, I mean I can chug hard cider. I love it, but hey maybe its something in the hooch. Ever heard of other people having trouble drinking apple brandy? I drink high quality commercial apple brandy all the time with no issues, but its also 8 years old. I have another apple juice wash finishing fermentation, so my plans are to strip it and then add this last hearts blend to the spirit run. I typically run at 3 drips per second. As far as 24-48 hrs letting the jars vent, aren't you worried about evaporation? It's not like you get to concentrate it, ethanol just disappears into thin air. Do you cover with coffee filters? Thanks for all the links, and I have read most of them but I found the methanol flame test very interesting. And I always do the flame test indoors, away from the alembic. I think the best take home from all of the responses was for me to get dozens of more runs under my belt. You're are exactly right. Just looking for answers is all. I will get this nailed down. I'm going to start closing my eyes when I sniff. Thanks!
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Re: Pot Still Vapor Temperature

Post by kimbodious » Fri Jul 24, 2020 9:17 pm

There is a lot to learn, You will learn a lot by reading and following the kiwistiller guide. Get an understanding of the basics first before being distracted by flametests and attempting making cuts on the fly.
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Re: Pot Still Vapor Temperature

Post by Beerswimmer » Fri Jul 24, 2020 9:35 pm

What everyone else said, trust YOUR senses, except your eyes on a thermometer! Don't do flame tests anymore, they don't really show anything except that it's flammable. Really. It's an old thing that doesn't make any sense in the modern world. And as for evaporation, as long as it's not above room temp you'll mostly only lose the bad stuff in 24-48 hours. And yes, coffee filters to cover your jars!
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Re: Pot Still Vapor Temperature

Post by NZChris » Fri Jul 24, 2020 10:28 pm

I don't trust this 48 hour airing idea that is being bandied about on forums these days, especially when it includes having angels partying up large on perfectly fine middle hearts jars. I'm not aware of any research that confirms it's a good idea, or of any commercial distillers of quality products that do it.

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Re: Pot Still Vapor Temperature

Post by Hambone » Fri Jul 24, 2020 10:45 pm

I think temps are useful for your (identical) wash, or your low wines, on your still. Taste should confirm any cuts, of course. I keep records and they show that temp (and therefore ABV) is a repeatable measure for repeatable conditions...
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Re: Pot Still Vapor Temperature

Post by Corsaire » Sat Jul 25, 2020 1:36 am

I agree, you can't use anyone else's numbers. You can use your own based on your own observations.

Regarding apple brandy headaches, I recently had a pretty bad Calvados while in France. I had just one glass and a hangover...
First time an apple brandy gave me a headache. I don't drink a lot of it though.

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Re: Pot Still Vapor Temperature

Post by Saltbush Bill » Sat Jul 25, 2020 1:52 am

NZChris wrote:
Fri Jul 24, 2020 10:28 pm
I don't trust this 48 hour airing idea that is being bandied about on forums these days, especially when it includes having angels partying up large on perfectly fine middle hearts jars
Chris we all have different ideas on the time that things can be aired ........I dont think much of you method either......i know of quite a lot of experienced hobby distillers who air cuts for longer than 48 hours.
As I've said before.....you must have particularly thirsty Angels at your house.
Most of what I loose by airing for longer is the shit that I dont want in.my barrels.
As with most things distilling its personal choice and what works for you.

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Re: Pot Still Vapor Temperature

Post by TDick » Sat Jul 25, 2020 9:05 am

ParrotHead wrote:
Fri Jul 24, 2020 8:23 pm
You guys are awesome. Maybe I just needed someone to tell me to stop listening to all the temperature folks writing the books.
But
ParrotHead wrote:
Fri Jul 24, 2020 8:23 pm
I do think that around 90 deg C is a good marker for me to take cuts for heads-hearts transition.

Just looking for answers is all.
I read this thread because I have a copper pot & thought I'd learn something new.
I shouldn't have done that - folks THAT KNOW are repeating the same thing written here years ago.
Because they work.

I have a thermometer and yes I watch it out of curiosity. Even though I KNOW it means absolutely nothing compared to LISTENING to my pot and putting my hands on it.

It would appear you are looking for the answers you already believe to be correct.

Even when everyone here is telling you they are not.
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Re: Pot Still Vapor Temperature

Post by bluefish_dist » Sat Jul 25, 2020 9:43 am

The temperature only tells you the abv at the still head. It’s not some magic way to do cuts. It changes due to atmospheric pressure, boiler abv, and power input on a pot still. On a reflux still the reflux rate and number of trays also effect your still head abv.

If you do lots of runs of exactly the same fermentation, you might be able to do cuts by temperature, but it’s only after you figure it out from lots of previous runs. Change the boiler abv or power and the cut points will change. I got pretty good at making cuts by volume, but it took 100+ runs. Even then, I just used that information on where to start tasting.

On a column still, I can take off the whole run within .5degf from start to finish. I believe still head temperatures are important to controlling the process, but they are not useful for cuts.
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Re: Pot Still Vapor Temperature

Post by ShineonCrazyDiamond » Sat Jul 25, 2020 10:28 am

Here's a fun experiment. You know what pure water taste like, right?

Get you a quart jar. Put in 500ml of your cleanest spring water. Then add 18ml of apple cider vinegar. Shake it up.

Take a sip. Do you taste the vinegar? I bet your left nut you do. Even though 96.5% of that solution is pure water, it makes a difference what that other 3.5% is. It's the same with alcohol. You can take everything off at 96.5%, at what ever temperature you want. But in the end, that 3.5% is made up from the happiness, or complaints of the yeast in the ferment.
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Re: Pot Still Vapor Temperature

Post by Saltbush Bill » Sat Jul 25, 2020 1:33 pm

Good analogy SOCD :thumbup:

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Re: Pot Still Vapor Temperature

Post by NZChris » Sat Jul 25, 2020 2:31 pm

Saltbush Bill wrote:
Sat Jul 25, 2020 1:52 am
NZChris wrote:
Fri Jul 24, 2020 10:28 pm
I don't trust this 48 hour airing idea that is being bandied about on forums these days, especially when it includes having angels partying up large on perfectly fine middle hearts jars
Chris we all have different ideas on the time that things can be aired ........I dont think much of you method either......i know of quite a lot of experienced hobby distillers who air cuts for longer than 48 hours.
As I've said before.....you must have particularly thirsty Angels at your house.
Most of what I loose by airing for longer is the shit that I dont want in.my barrels.
As with most things distilling its personal choice and what works for you.
There is an optimum for everything and I've never seen any research that points to an optimum for airing. There will also be different optimum times for different products, climates and humidities, (and newbie stupidity, like thinking it's a good idea to point a fan at the line up :roll: ). Also, the benefit of airing increases with the amounts of nasties present that you want to get rid of, so early jars will benefit far more than middle jars. My middle jars smell nice, so airing them for any length of time would only lose fine esters and alcohol that I want to include in my heart cut.

I did an experiment with a sample of alcohol that I'd managed to concentrate the oils in to the point where they had precipitated into a globule. This was left airing. The alcohol and water evaporated first, leaving the globule behind. The globule disappeared a couple of days later. The order in which the components left the jar makes me skeptical of supposed advantages of airing tails jars, especially for extended periods of time.

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Re: Pot Still Vapor Temperature

Post by Kareltje » Sat Jul 25, 2020 3:27 pm

ParrotHead wrote:
Fri Jul 24, 2020 11:57 am

Other online documents say that 87.8 degrees C (190 deg F) is where hearts begins. I have a new Bourbon making book that does all the keeper cuts starting at 83 deg C using a pot still ! Based on my pot still this would expose you to methanol and definitely a bad headache if not worse. Based on what I have seen thus far, 80-83 deg C is where heads really starts flowing. So WTF?
Sorry??

Apart from the methanol-nonsense: at 87,8 dg C during my spirit run, I would start to be looking out for the tails. And I would hope my heads are already gone around 83 dg C, so the heart has already started.

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Re: Pot Still Vapor Temperature

Post by bilgriss » Sun Jul 26, 2020 5:14 am

My current theory on (48 hours plus) vs overnight airing before making cuts.

I think that a longer airing makes it easier to distinguish differences by SMELL, particularly if you don't have much experience yet. Waiting makes that difference more pronounced.

I think that if you have some experience, the differences become more obvious as well, at shorter times. I would (totally guess) that the longer you let it sit, the more aromatic qualities you might lose, and there could be a point of diminishing return, such as what NZChris is implying. But that doesn't mean it's a bad idea. It means there's a learning curve, and you should pay attention until that nuance becomes clear.

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Re: Pot Still Vapor Temperature

Post by Hambone » Sun Jul 26, 2020 5:24 am

Even though we've migrated a bit from the OP topic...

I collect heads and tails in small jars, while obvious hearts (by taste/ smell) go into gallon jugs.

I leave the jars to air, checking daily. If they pass my taste test, they get added to the heart cut. If not, I leave them another day. Or 3. Or 5 if I forget.

I've been able to add further heads on some runs with confidence, not losing much of those to the angels. But there is no reason in my mind to air out obvious heart cuts, I don't see what that would add. And I don't need so many damn little jars sting around...
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Re: Pot Still Vapor Temperature

Post by ParrotHead » Wed Jul 29, 2020 7:54 pm

Thanks for all the great feedback. I'm not cutting on the fly. I'm smelling and tasting off the still to determine when to start making my cuts. When I do a stripping run I notice that the swan neck vapor temperatures starts into heads high, around 86 deg C and for rum and brandy my heads to hearts transition is occurring somewhere around 90 deg C, which I understand is subject to change for everyone. For spirit runs, the heads starts much earlier around 80 deg C and its a much wider distribution of the heads. Once I smell and taste a decrease in acetone/solvents and an increase in EtOH I start collecting my cuts, usually at 100-150 mls each. Brandy is a bit tougher and can use a lot more cuts than rum to get to the clean EtOH. Obviously it has a larger heads fraction, and less hearts,from what I have experienced. It might be better to just drink the hard cider instead of wasting 5.5 gallons of hard cider on only one 750ml bottle of hearts apple brandy.

There comes a point when its so clean I just know its time to hook up the parrot and start watching my ABV until 50%, where I then start taking tails cuts through the 40's. Brandy is tough because the heads solvents seem to be masked by the wonderful fruit aroma. Thanks to airing out the cuts for 24 hours, and then diluting can you really smell the funk that is behind the fruit esters. It's an awkward in-your-face solvent close to paint thinner. I think this is where I got into trouble by not airing it out and I could not smell the cutoff even when diluted. They all smelled the same, like apple cobbler. It literally makes you want to take all of the heads and blend it in with the hearts. It smells so good, but has some bad stuff hidden in there you have to air out to get to. I also notice that the taste of bitterness is easier to find the cutoff when you air it out. It's very noticeable as an astringent bitterness, not even like a green tannin bitterness. It's a chemical bitterness.

Well anyway, sorry if I pissed some people off, but this is the novice section of the forum. All you experts out there were at one time a novice. So relax, don't worry, have a home distilled spirit. Or a home brew.
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Re: Pot Still Vapor Temperature

Post by NZChris » Wed Jul 29, 2020 10:25 pm

You tell us you're not cutting on the fly, but the way you describe your runs, you are doing what I do when I cut on the fly. I only do what you're doing for repeat products where it doesn't matter much if I don't get it quite right.

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Re: Pot Still Vapor Temperature

Post by ParrotHead » Thu Jul 30, 2020 8:49 am

Oh ok, I thought cutting on the fly was not collecting any cuts at all. I am still collecting at the end of heads where the noticeable transition to hearts begins. I typically have 7 cuts from heads to hearts and usually only include a few of them that pass the smell and taste test. Works well for rum, but the issue was with apple brandy, and I think the issue has been resolved with letting it air for 24 hours. There are much more heads with apple brandy and it results in more cuts until its really clean. I'm also doing stripping runs to get better separation because I felt as though there was some smearing going on with heads to hearts that I could not detect? Anyone do just one spirit run off the original wash. I get a very intensely flavorful rum that way and its really good with no headache but can sometime feel tired the next day, so for that reason I think stripping will provide better fractionation especially with an alembic pot and no reflux. However with this added stripping run I collect (2) 750ml bottles whereas with no stripping I collect (3) 750 ml bottles (5.5 gallon wash at 12.8% ABV). Major noticeable difference between the two is less intense rum aromas and a lighter final product with stripping.

I appreciate all the help. I just need to keep at it and continue to learn contrasts between solvent aromas with different types of spirit. So far I have only done rum and apple brandy. Will dabble with bourbon once I get these two locked in to a good consistent product. Give me a year and I think I will have it nailed down. LOL
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Re: Pot Still Vapor Temperature

Post by jonnys_spirit » Thu Jul 30, 2020 9:24 am

If you do three to four strips you can fill the boiler with low-wines and I'll typically collect 20-30 fractions which increases the take and makes the fractions easier to differentiate - at least for me. I'll collect smaller fractions until I'm into the hearts then larger fractions until I feel like I'm about to approach tails then smaller fractions for a bit until I'm ready to be done with it.

Some folks do a 1.5 run where they collect one or two strips and then top up with fresh wash to fill the boiler (or 3/4 full or whatever) then do a spirit run. Something between a one-and-done and a double-distillation protocol. Plenty of room in that middle ground for options depending on how long you run each strip and how much low-wines:fresh-wash you mix and what the eventual spirit-run boiler charge ABV is...

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Re: Pot Still Vapor Temperature

Post by ParrotHead » Thu Jul 30, 2020 12:43 pm

jonnys_spirit wrote:
Thu Jul 30, 2020 9:24 am
If you do three to four strips you can fill the boiler with low-wines and I'll typically collect 20-30 fractions which increases the take and makes the fractions easier to differentiate - at least for me. I'll collect smaller fractions until I'm into the hearts then larger fractions until I feel like I'm about to approach tails then smaller fractions for a bit until I'm ready to be done with it.

Some folks do a 1.5 run where they collect one or two strips and then top up with fresh wash to fill the boiler (or 3/4 full or whatever) then do a spirit run. Something between a one-and-done and a double-distillation protocol. Plenty of room in that middle ground for options depending on how long you run each strip and how much low-wines:fresh-wash you mix and what the eventual spirit-run boiler charge ABV is...
Yeah I think this technique will be easier once I have a stock pile of finished spirit. LOL 20-30 fractions? I think my nose would burn out by the time I got through all of that. I just get to a point in the heads and tails that its not even worth continuing to smell because they all smell like acetone, ethyl acetate, paint factory after a certain point (or burnt corn and veggies for tails), so this is why I collect until the transition areas and find the cut off there. I do use ground coffee to clear my nose when it starts to burn out on minor differences. Might be interesting to do small cuts all the way through just to see the differences in solvents. Thanks for sharing. Have you ever compared a single distillation to a double distillation for volume and flavor, with same recipe? You are running an alembic right? Do you think there is pronounced smearing of heads congeners well into hearts with a single run? The flavor is so intense, its hard for me to strip that out with a second distillation. Its still incredibly smooth. Just trying to work through the pros and cons.

What ABV% for your low wines spirit run? I've noticed it runs faster at 25-30%, but do you gain or lose flavor by diluting to 20%? I think its just personal preference and the average is ~28% from what I've read.
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Re: Pot Still Vapor Temperature

Post by jonnys_spirit » Thu Jul 30, 2020 2:05 pm

I don't know about heads and congeners and all that fancy technical talk lol but I'll fraction out the spirit run into usually about 24 or so jars/fractions and let it air for a couple days and test/smell/taste different blends of the fractions over that 3-4 days/evenings so I can get a good idea of what a glass or three of the different blends is like. I usually try to get my SO to sit down and write some notes about what they smell/taste too in the distillers log for any of the fractions and within a bit less than a week will choose a white cut and a barrel cut for aging on oak.

I typically run the flavored spirits low-wines to between 35-40%ABV. I've been considering doing a 1.5 run and diluting down to maybe the upper 20's%ABV with fresh wash or something like that just to see about the flavor.

If you add water to low wines it dilutes the flavor. If you add something else with flavor like fresh wash or backset then it's sorta like the difference in cooking something with say chicken stock or water... Add some wine into your marinara for the flavor.... add water to your marinara if you like that water flavored marinara ha ha!

Cheers!
-jonny
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i make stuff i break stuff
water into whiskey into water
just getting started in home distilling - been drinking for decades
16g copper pot still, 10l alembic, and a column or two
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Stibnut
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Re: Pot Still Vapor Temperature

Post by Stibnut » Sat Aug 01, 2020 1:43 am

I'm very much a novice at home distilling, and I'm just about to start my first brandy wash with a Concord grape wine base. But I'm also a chemistry geek and I have access to a GC in my job as a lab tech for an industrial ethanol producer. As it happens, I just did a set of tests using very pure ethanol mixed with other compounds, diluted with water down to 15% ABV and distilled on a heating mantle using a glass retort and a Graham condenser. This simulates a pot still. I've seen some stuff you might find interesting, and I'll post my data in its own thread soon.

The first post that NZChris linked to talks about how methanol concentrates in the tails more than in the heads, compared to ethanol. If you look at the third image, you'll see something that is the opposite of conventional wisdom about which compounds end up in which cuts in a single pot still run: at ethanol concentrations that occur in any fermentation (<25%), the most volatile alcohols are the fusel alcohols isobutyl alcohol and isoamyl alcohol (aka 3-methyl-1-butanol) while the least volatile is methanol. Never mind the fact that isobutyl alcohol boils at 108 C and isoamyl at 131 C, while methanol boils at 65 C and ethanol at 78. This is true: I have seen the data and will post it in a thread soon.

In a single pot still run, the longer-chain alcohols like isobutyl and isoamyl end up disproportionately in the heads/foreshots (along with acetaldehyde and ethyl acetate, which make up most of the headsy smell) while methanol ends up disproportionately in the tails. This is because water pushes out the more hydrophobic compounds including the fusel alcohols while pulling in the most hydrophilic ones like methanol, and this effect is more powerful than the difference in boiling points for pot still runs. The hydrophilicity/hydrophobicity effect diminishes so that the opposite is true for high ABVs, as you'll see if there is lots of reflux or if you are distilling something above about 50% ABV. But for a pot still, the order is the opposite of what you would think from the boiling points.

The flame test is wrong not just in that it's an unreliable guide to methanol, it's the opposite of correct: methanol burns with a clean blue flame, while the more hydrophobic stuff burns orange because it contains more carbon to generate soot which glows orange at typical flame temperatures. People have learned to associate orange flames with fores and heads because there is lots of carbon-heavy stuff in those fractions. But that's not where the methanol is - it appears throughout the run but is somewhat more concentrated in the tails.

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Re: Pot Still Vapor Temperature

Post by Brew bama » Sat Aug 01, 2020 7:55 am

I look forward to that post Stibnut.

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Corsaire
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Re: Pot Still Vapor Temperature

Post by Corsaire » Sat Aug 01, 2020 9:21 am

Great post.

Can we sticky this? Should maybe help convince people that a pid is not ideal, that you don't toss methanol with the fores and that lighting spirits on fire is not only a safety hazard but a downright flawed method.

Perhaps add a dumbed down tl:dr part at the beginning.

I'm looking forward to any data you can post. I'll try my best to understand it :-)

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