Reflux vs Pot Still Temperatures

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undercover
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Reflux vs Pot Still Temperatures

Post by undercover » Mon Aug 19, 2019 2:20 am

Hi,

Reflux Mode

I've been successfully reflux distilling GNS with my boka, with the expected vapour temperature range:

77.1°C FORES/HEADS collection

77.9°C HEARTS (average, based on atmospheric pressure)

78.8°C TAILS collection

Pretty much azeotrope throughout collection, but it does take a serious amount of time and reflux management to achieve this (as expected). So all is good with reflux mode.

Pot Still Mode

When run in pot still mode, LM valve wide open on the lowest power setting I'm getting really good abv, 95.5% Fores/Heads dropping steadily to 94% Hearts, down to 93% tails and onwards.

However, the vapour temperature range behaves like it does in reflux mode, starts at 77.1°C to around 78.8°C when tails arrive.

Pot still cut temperatures are mentioned everywhere on these forums, such as this:

Collect Fores/Heads up to 80°C
Collect Hearts up to 91°C
Collect Tails up to 96°C

If these temperatures are vapour temperatures (taken at the outlet), why doesn't my still run with a huge temperature range like these when in pot still mode?

I can't work it out.

I've left the packing in the column, so maybe it's refluxing too much, even with the LM valve wide open? However, it's literally on the lowest power achievable without stalling the flow (indicated by the high abv), so I shouldn't really have any reflux occuring and it should behave like a pot still...

Any help would be appreciated.

UC

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Yummyrum
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Re: Reflux vs Pot Still Temperatures

Post by Yummyrum » Mon Aug 19, 2019 2:37 am

Do you by any chance have a "pure Distilling" still or " Ultra pure still " ?
Reason I ask is because these stills have a restricter in the valve so that even when you run it wide open , it's still a reflux still ... they kinda make it idiot proof but make it hard for those with a few clues .

But I'm confused ...are you re-distilling GNS from a store ...thats already close to azeo ......it should always be dilluted down first .

undercover
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Re: Reflux vs Pot Still Temperatures

Post by undercover » Mon Aug 19, 2019 2:51 am

Thanks, I think you've nailed it.

The LM needle valve inlet diameter (within the valve body) is only a couple of mm, tiny compared with the pipe diameter 12mm. It's still refluxing...

No I'm cleaning up super cheap vodka. It's full of heads and tails (as you can imagine, hence the price) and trying to yield as much GNS as I can to try and find the limits of my still. As you've pointed out, it's still running in reflux mode (but not as well). I thought something wasn't right.....

I'll remove the valve completely and re-try in "true" pot still mode. I guess I should expect to see the pot still cut temps as above?

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Yummyrum
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Re: Reflux vs Pot Still Temperatures

Post by Yummyrum » Mon Aug 19, 2019 4:19 am

Yes you should see closer to those temps without the valve .

With no refluxing the packing in the column doesn’t do much once its up to temp.

undercover
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Re: Reflux vs Pot Still Temperatures

Post by undercover » Mon Aug 19, 2019 4:29 am

I dilute the boiler charge to 30%. I think this is a good balance of safety versus purity/run time.

You're right, it's mostly curiosity. I want to run the vodka in pot still mode to define the still parameters (power, cut temperatures versus taste, abv etc) so I can produce flavoured spirits consistently. I also want to see the "standard" pot still cut temperatures before my very own eyes!

Thanks for the info on the packing. I'm glad I don't have to remove it, that would be a right hassle. Although, I think I'll remove it for messy stripping runs.

OtisT
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Re: Reflux vs Pot Still Temperatures

Post by OtisT » Mon Aug 19, 2019 8:36 am

Undercover,
There are not a lot of threads or folks on HD that recommend making any pot still cuts by temp. I see a lot of folks who come to HD with that info from other forums or utube videos, but that logic does not go far here. Where a person should make cuts may vary in temp from run to run, style to style, so while it’s a good ballpark it’s a bad way to make your final cut decision. I use temp to know when it’s time to end a run, but that’s about it. Cut decisions are made by smell and taste.

Otis
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Twisted Brick
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Re: Reflux vs Pot Still Temperatures

Post by Twisted Brick » Mon Aug 19, 2019 9:44 am

OtisT wrote:
Mon Aug 19, 2019 8:36 am

Where a person should make cuts may vary in temp from run to run, style to style... cut decisions are made by smell and taste.
Otis
+1

Sage words to live by.

Nonetheless, I see where you are coming from, Undercover. Your curious side just wants to acknowledge the takeoff taste/smell associated with any given temp (ABV).

Producing flavored spirits from a pot still consistently will take many spirit runs, and your learned senses will serve you well.
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