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Cleaning the inside of copper still


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#1 PeteB

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Posted 26 July 2011 - 07:09 PM

As some of you would have noticed, I have been running fermented cherries in my pot still.

The inside now has a brownish green deposit on it. It is a copper compound, not cherry juice.

Any suggestions about the easiest way to remove it, and how important is it to get it all off?

#2 PeteB

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Posted 03 August 2011 - 07:31 AM

233 views of my post to date and no suggestions on cleaning. I thought this would have been a common task.

Further observation: after finishing the spirit run I switched the heat off and left an empty white plastic bucket under the spirit outlet.

The next morning the liquid in the bucket was sky blue. it tasted extremely bitter. Typical copper sulphate colour. The fermented cherries did not have SO2 added but I assume there must have been quite a lot of sulphur compounds formed during fermentation.

I am sure I will need to scrub the inside of the still before my next whiskey run in a couple of days.

Do I get in there with a scouring pad, or vinegar, or bicarb, or caustic?

#3 JohnD

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Posted 03 August 2011 - 08:00 AM

I would do caustic first then citric or whatever acid you use. Don't scrub, fill the whole thing up all the way up into the helmet with caustic and water, 180F, rinse, then fill the whole thing up with the acidified water.
Leave each of them in there for 20-30min. That will get it out.

#4 ViolentBlue

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Posted 03 August 2011 - 11:38 AM

citric acid works good cold and better hot. and like was said before, don't scrub the copper to remove the copper compounds only scrub any deposits left over from the cherries.

#5 ammocrypta

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Posted 04 August 2011 - 07:28 AM

This brings up another question - is this a common issue with cherries, and is there something that could perhaps be done about it while in the fermentation stage?

#6 JohnD

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Posted 04 August 2011 - 08:00 AM

At what temp was the fermentation held and how were the cherries processed? Pits removed?

#7 bluestar

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Posted 04 August 2011 - 08:18 AM

This brings up another question - is this a common issue with cherries, and is there something that could perhaps be done about it while in the fermentation stage?


The copper is removing sulfurous compounds, making copper sulfates and sulfide (blues, greens, and black). They are in the cherry juice, and you want them removed.
If you are adding more sulfurous compounds as part of your process to disinfect, eliminating that could reduce the amount of deposits, but not eliminate it all. So, the
only other thing to do would be to remove sulfur prior to going into the pot. Best way to do that: copper!!!. You could preheat the juice and run it hot through a copper
catalyst: essentially a structured packing. That way you can refresh and replace the packing regularly instead of your pot! But you won't eliminate the cleaning step, just
shift it. And you will still have to clean the pot, just with less deposit so perhaps less often.

#8 ammocrypta

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Posted 04 August 2011 - 03:58 PM

The copper is removing sulfurous compounds, making copper sulfates and sulfide (blues, greens, and black). They are in the cherry juice, and you want them removed.
If you are adding more sulfurous compounds as part of your process to disinfect, eliminating that could reduce the amount of deposits, but not eliminate it all. So, the
only other thing to do would be to remove sulfur prior to going into the pot. Best way to do that: copper!!!. You could preheat the juice and run it hot through a copper
catalyst: essentially a structured packing. That way you can refresh and replace the packing regularly instead of your pot! But you won't eliminate the cleaning step, just
shift it. And you will still have to clean the pot, just with less deposit so perhaps less often.


My question still stands... if there was no sulfur added pre-fermentation, why are sulfur levels so high? Common with other fruit fermentations as well?

#9 PeteB

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Posted 04 August 2011 - 04:24 PM

At what temp was the fermentation held and how were the cherries processed? Pits removed?



I will ask the cherry farmer the details and get back to you. The "wash" he delivered to me had some cherry pits and some stalks, but only a small % from the 3 tons of cherries he used. I have read that stalks are not good for some reason, maybe they contain a lot of sulphur compounds! He said fermentation temperature was around 25C (77F)
A local distiller suggested that after pressure washing the cherry gunk off, I just run the still with water only. I have done that with 2 small amounts of water and the condensate is now very clear and has almost no taste.

#10 PeteB

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Posted 04 August 2011 - 06:13 PM

I am a little concerned about putting caustic (sodium hydroxide) in my copper pot.

I assume the blue deposit on the copper is copper sulphate. Copper sulphate is soluble in water, even more so at around 100C. Copper sulphate plus sodium hydroxide forms copper hydroxide which is INSOLUBLE.

If I can wash all the coper sulphate out with water that is good. Insoluble copper hydroxide will probably stay in the still, not sure if that is good or bad. Some copper sulphate is/was in my copper condenser. If that turns to hydroxide I am not sure if it will come out with the spirit as a solid and be filterable or stay attached to the copper forever!

Also, citric acid on copper forms a chelate. In water at normal temperatures the chelate slowly releases copper. What will happen next time I run the still? Will the heat dump all the copper into my spirit causing a metallic taste?

The above ramblings are just chemistry THEORY. (E&OE it is 40 years since I studied chemistry)

A little bit of theory can be a hindrance, but it can make you question a process.

Practical suggestions from you out there who have "been there, done that" is the best.

Thanks for the help so far.

#11 Denver Distiller

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Posted 04 August 2011 - 09:07 PM

SImple CIP process, assuming you have a CIP sprayhead in your still

Rinse with tap water. Brush out any large solids.
Circulate caustic at 50 C. Inspect for solids, use brush w/plastic bristles if needed.
Rinse w/tap water.
Circulate food grade citric acid at 50 C. Inspect.
Rinse w/tap water.

That's it. That'll get out any soil you'll come across. I've used it for fermented whole cherries, bourbon mash, rye mash, whole peaches, whole apples, whole cherries, beer, molasses, cane syrup, potatoes, wheat, Gin, Absinthe, etc.....the whole shooting match. The only thing I've ever had to do is increase the caustic concentration slightly, and that's a rare case. And I should add if you have really hot water, you may have to use acid first, to get the mineral coating off before attacking the proteinaceous soils, then caustic, then acid one last time.

Keep it simple. Keep it safe. IMHO, using water hotter 50 C is unnecessary and dangerous.


If you don't have a CIP system, then put the chemicals in the still, warm it up making sure you cover the heating element (or jackets, or whatever), and use a brush. If that's your method, it's even more important to use gentle temperatures.

Cheers

#12 PeteB

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Posted 04 August 2011 - 10:46 PM

Thanks Denver Distiller. You have given me the confidence to do what other posts have suggested.

I don't have a CIP system so I will be using a brush on a long handle.

Interestingly I was listening to a radio programme a few days ago on removing stains from fabrics. The speaker said to change the pH on the stain several times by using vinegar followed by bicarb of soda. This is what you are doing in the still:rolleyes:



The only question left is what are the concentrations of caustic and citric acid?

#13 Rich Morgan

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Posted 01 September 2011 - 04:26 AM

233 views of my post to date and no suggestions on cleaning. I thought this would have been a common task.

Further observation: after finishing the spirit run I switched the heat off and left an empty white plastic bucket under the spirit outlet.

The next morning the liquid in the bucket was sky blue. it tasted extremely bitter. Typical copper sulphate colour. The fermented cherries did not have SO2 added but I assume there must have been quite a lot of sulphur compounds formed during fermentation.

I am sure I will need to scrub the inside of the still before my next whiskey run in a couple of days.

Do I get in there with a scouring pad, or vinegar, or bicarb, or caustic?


Here is what we do, and all our stills are 100% copper. We use a weak 5% sulfuric acid solution, doped with 1% hydrogen peroxide. It cleans like nothing else. rinse, We then passivate with a 3% caustic soda solution, rinse then a 1% citric acid.

rich..

#14 bradocaster

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Posted 18 November 2011 - 04:01 PM

is the passivization a rinse type situation? is this process the pot only, or is it the entire still?
Thanks, Brad

#15 coop

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Posted 19 November 2011 - 10:07 AM

Todd, I am using a granulated Sodium Silicate for my caustic solution. How much would you use to do a good job? I am using 40 gallons of water. The same question goes for citric acid before final rinse with fresh cold water. Coop

#16 Rich Morgan

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Posted 21 November 2011 - 07:07 AM

is the passivization a rinse type situation? is this process the pot only, or is it the entire still?
Thanks, Brad


Passivation (neutralisation) is a rinse of whatever was acid washed. We flood the entire still, column, condensers when we clean.




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