Temperature with Pot Still

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Swampdrop
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Temperature with Pot Still

Post by Swampdrop »

Hi All,

I’m new to distilling and did my first run today with my pot still. I have spent the last few months reading everything I can get my hands on and I have found this forum a wealth of information. I have a question regarding temperatures. I have read that a lot of people don’t keep track of the temperature that their still is running at citing that it is too inaccurate and that every still is different. I have a thermometer on my still and I was keeping track of it today when my still was running. I checked the temperature of the liquid in the still just prior to the first drips starting to come out and the temp was 85c. I thought that methanol would have come off the liquid at a lower temp then this. The temperature stabilised in the 90’s c and I assume this is the heads, hearts and tails. I kept running the still and collected several litres of distillate in separate containers and stopped collecting when it dropped below 30%. Should I be concerned that my still only started to produce the first drops of distillate at 85c? I thought that the process would have started at a lower temp?
Dnderhead
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Re: Temperature with Pot Still

Post by Dnderhead »

if that is boiler temperature it will vary with the percentage of alcohol that is in the wash.
if it is vapor temperature it will clime as the alcohol is depleted.
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Husker
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Re: Temperature with Pot Still

Post by Husker »

Swamp,

This is one of the 'myths' beginners often get confused with. You are boiling a mixture of methanol (slight amount) acetate (slight amount) eythl acetat (slight but a little more), ethanol (5 to 15%) and water (and a few other things tossed in for good measure). These items are miscible. They can not easily be separated.

Now, as you have stated, each of these has a different boiling point. One of the first things you need to 'forget' in your knowledge base, is that stuff with the lower boiling point will boil off before the stuff at a higher boiling point. This simply does not happen, exactly like that. Yes, the lower boiling point stuff 'does' boil off first (early on), but it does not boil off all on it's own. If it did, then distillation would be simple, and we would have an easy way to make 100% ethanol, by simply boiling slowly and below 100°C, and end up with just ethanol. Would be nice if it happened like that, but it does not.

What DOES happen, is you are working with a mixture, and this mixture is boiling. The vapor coming off this mixture IS higher in concentration of the lower boiling point material, but it is not 100% made up of them.

The easiest way is to 'see' what is happening, is to simply ignore all of the other items and make an assumption that you have PURE water and PURE ethanol mix. I will make this case, and assume that you start out with a 15% ethanol 85% water mixture. Water has a boiling point of 100°C and ethanol boils at 78°C (or close to that). Now, this 15% ethanol mix will NOT boil at 78°C but will boil at about 90°C or so. This vapor is NOT 15% ethanol, and is not 100% ethanol. It is however stronger in percentage of ethanol than what is in the boiler (this is why distillations 'works'). This vapor coming off at this given moment, will be in the range of 65% ethanol. But our mix is 15% and the vapor is 65%, so as you can see, you will be reducing the ABV% in the mix in the boiler in a rapid manner, since you are removing much more ethanol (percentage wise), than you are removing water.

Now, continuing that forward: As this percentage drops, the temperature of this boiling liquid will be rising. Say you have reduced the boiler ABV to 8% (removed a little over 1/2 the total ethanol or so, and some of the water, but a lot less than 1/2 of the water). At this time, the boiling point has risen to about 94°C, and the percentage of ethanol in the vapor has reduced to about 50%. But you are still getting a mix of the two. Take it further, say you have distilled out most of the ethanol, and now the boiler only contains a mixture that is 2% ethanol and 98% water. It would boil at about 99°C and the vapor would be about 10% ethanol.

Now, the same principle is happening when there are multiple liquids that are miscible (i.e. they 'join' together and are not easily separated). When you boil, you will get higher concentrations of each, than are in the boiler, and this concentration left in the boiler will drop off since a higher percentage has been removed when viewed over time. But you will still end up with a mix of methanol, acetone, ... ethanol, water, ... during the time when there is still some of that liquid in the boiler. The proper way to cut out the 'heads' (and tails), is to remove the part of the run where the highest concentrations of these 'unwanted' items are at. These other items do make up a much smaller overall starting percentage than the ethanol. Thus, the boiler will run out of them (or almost run out), LONG before it runs out of ethanol. So almost all of these unwanted items can be removed, prior to collecting the part you want to keep.

Even though this was a long winded reply, it is still pretty much simplified. What is happening within that liquid to vapor transition within a mixture with multiple boiling points is pretty complex, but if you simply realize that you get a higher percentage vapor (of the most volatile stuff), than what you boiled out of, you get most of the insite.

The 'art' (yes it IS an art) of distillation, is simply learning how to properly control this phenomenon properly, getting the best results.

A good place to look for more detailed information, is the link at the top of each page, to the 'parent site'. Then go to the theory section. It is chock full of information. It may make your head hurt or spin, but the info IS there ;)

H.
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rad14701
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Re: Temperature with Pot Still

Post by rad14701 »

Swampdrop, the charts in this topic are remakes of the original on the parent site which depict the process... You may find them helpful...
Swampdrop
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Re: Temperature with Pot Still

Post by Swampdrop »

Hi Dnderhead and Husker,

Thanks for the reply. I'll have another read of the theory section of the parent page. Thanks for the detailed reply Husker I'm much clearer on what's going on in that pot of mine now. Thanks again. Happy Stilling.

Swampdrop.
Lagerman64
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Re: Temperature with Pot Still

Post by Lagerman64 »

Please help out here, I have a pot still, I'm still a little confused regarding temperature. Should I go high and fast or low and slow. The instructions I have been following say I should stablize the column @ 184 degree F (84C) and let it climb naturally ending the run around 192 (88C). On average I get a better flow rate around 186 (85.5C). I have a thumper and am guessing that with thermal loss it's probably running around 172-182 (78-83C) when stabilized and goes through the process. I'm thinking low and slow is the way to go to get a higher ABV extraction rate, but if it's a stripping run go high and fast? Am I on the right track?
Dnderhead
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Re: Temperature with Pot Still

Post by Dnderhead »

your right in your thinking. but with a thumper you should not have to "strip" unless your making vodka.
Lagerman64
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Re: Temperature with Pot Still

Post by Lagerman64 »

Thanks for confirming that, I ran a batch of vodka yesterday it came out quite flavorful, it should have been more neutral. Now I know where I went wrong, however good it turned out, yum. I love you guy's :twisted: . P.S. Have a gin run going low and slow, hitting the 12 hour mark as I type this.
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