Filtration or Racking after Copper Treatment?

[Jay Kenney]

I've got a small batch of cider that developed H2S. I trialed it, and have treated it with CuSO4 and now wonder about what happens to the precipitate, which I think, if the internet and my HS chemistry are correct, would be copper sulfide and sulphuric acid. H2S + CuSO4 --->CuS +H2SO4. I understand that the copper sulfide would show up in cider as black lumps or powder and I'd like to filter and/or rack as appropriate. [Not sure what happens to the sulphuric acid; volatized? Reacts with other acids in the cider?]. Suggestions on filtration size, or are the copper sulfide particles too small to filter and the cider should just be racked leaving a generous amount of residue? 

[Brian Drake]

Jay, I've had a few go this route and as I had several batches going, I cut my losses and dumped the first couple, but I'm drawing a battle line on this current stinker.  I have one now that smells like rotten egg-salad sandwich in a glass, and 2 months of aging, aerating, CO2 bubbling, multiple rackings and KMS doses haven't made but a small dent to the offensive stench.  I read quite a bit and was about to get some CuSO4, but was a bit nervous about getting my dilution correct.  I read some more and ran across this article:

https://midwestwinepress.com/2017/05/01/how-copper-fooled-us-all/

In sum, the story is that the black precipitate (CuS) is apparently (I haven't verified through my own experience mind you) a bit elusive in practice and that the conversion of H2S to CuS can reverse in certain conditions.  Also seems that there are opportunities for H2S and MeSH (Methyl Mercaptan) to be bound up (and disappear below perception threshold), but come unbound later. 

So, I skipped the CuSO4 and got both Reduless and Kupzit and I'm trialing both now - added 2 days ago, will rack tomorrow and see what happens.  Praying for a redemption story - this year's crop of Cascade hops is looking for a good home!  Good luck to you, Jay.

Cheers!

Brian

OOLLC

On Wed, Feb 5, 2020 at 9:33 AM Jay Kenney <kenne...@gmail.com> wrote:

I've got a small batch of cider that developed H2S. I trialed it, and have treated it with CuSO4 and now wonder about what happens to the precipitate, which I think, if the internet and my HS chemistry are correct, would be copper sulfide and sulphuric acid. H2S + CuSO4 --->CuS +H2SO4. I understand that the copper sulfide would show up in cider as black lumps or powder and I'd like to filter and/or rack as appropriate. [Not sure what happens to the sulphuric acid; volatized? Reacts with other acids in the cider?]. Suggestions on filtration size, or are the copper sulfide particles too small to filter and the cider should just be racked leaving a generous amount of residue? 

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[Jay Kenney]

That's a super interesting link. Thanks for sending it along. On first blush, I wonder if the amount of tartaric acid in apples is enough to bind up the CuS? But it's curious that no one has ever seen the precipitate and that racking and filtration does not seem to reduce the amount of copper. It is going to take a chemist to sort this out, but I'd be very interested to see how your trials turn out with Reduless and Kupzit. On your side, did you test for the presence of disulfides in your cider? My reading of the chemistry is that if your cider has converted simple sulfides into disulfides no amount of copper, aging aeration, bubbling or racking will do anything but make the problem worse. And that the only traditional treatment is to first break down the disulfides into sulfides again (using ascorbic acid) and then treat with copper. 

I'm also interested in the reappearance of H2S once bottled. My experience there is limited. But I just had a chance to drink some cider made in 2016 and bottled in 2017 last night that had been treated with both ascorbic acid and copper, but that was not done immediately before bottling. Rather the H2S emerged after fermentation early in the maturation phase, was treated and then continued to mature for another 2-3 months. Maybe that makes a difference, since "anoxic conditions seem to force latent H2S release," according to the linked article. 

In any event, do let us know your success with the alternative treatments. I read the package inserts for Reduless and they did not say anything about the possibility of treating both sulfides and disulfides--sounds like your batch would be a good test since the smell has been so persistent. 

And I'll be racking and filtering my small batch soon so will report back if I can see any of the elusive black copper precipitate. 

On Friday, February 7, 2020 at 12:01:18 AM UTC-7, Brian Drake wrote:

Jay, I've had a few go this route and as I had several batches going, I cut my losses and dumped the first couple, but I'm drawing a battle line on this current stinker.  I have one now that smells like rotten egg-salad sandwich in a glass, and 2 months of aging, aerating, CO2 bubbling, multiple rackings and KMS doses haven't made but a small dent to the offensive stench.  I read quite a bit and was about to get some CuSO4, but was a bit nervous about getting my dilution correct.  I read some more and ran across this article:

https://midwestwinepress.com/2017/05/01/how-copper-fooled-us-all/

In sum, the story is that the black precipitate (CuS) is apparently (I haven't verified through my own experience mind you) a bit elusive in practice and that the conversion of H2S to CuS can reverse in certain conditions.  Also seems that there are opportunities for H2S and MeSH (Methyl Mercaptan) to be bound up (and disappear below perception threshold), but come unbound later. 

So, I skipped the CuSO4 and got both Reduless and Kupzit and I'm trialing both now - added 2 days ago, will rack tomorrow and see what happens.  Praying for a redemption story - this year's crop of Cascade hops is looking for a good home!  Good luck to you, Jay.

Cheers!

Brian

OOLLC

On Wed, Feb 5, 2020 at 9:33 AM Jay Kenney <kenn...@gmail.com> wrote:

I've got a small batch of cider that developed H2S. I trialed it, and have treated it with CuSO4 and now wonder about what happens to the precipitate, which I think, if the internet and my HS chemistry are correct, would be copper sulfide and sulphuric acid. H2S + CuSO4 --->CuS +H2SO4. I understand that the copper sulfide would show up in cider as black lumps or powder and I'd like to filter and/or rack as appropriate. [Not sure what happens to the sulphuric acid; volatized? Reacts with other acids in the cider?]. Suggestions on filtration size, or are the copper sulfide particles too small to filter and the cider should just be racked leaving a generous amount of residue? 

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[Brian Drake]

Reporting back on treating for VSC:

Have used Reduless on a couple of batches recently - my first attempts.  One batch had a mild case.  Added 5g/19L and let it sit for a week.  Just racked and it's greatly improved - there's maybe a hint, but it's right at limit of (my) perception and I'm hopeful that it will disappear after aging for a bit longer.  Did notice a distinct coppery/metallic finish and wondered if that might be the copper from Reduless... but, also read through the thread history on the Group and found a clue that indicated that this could also be related to over-addition of malic acid (definitely went overboard...)

2nd batch had more VSC to begin with.  Same treatment as above - (5g/19L) and about a week again.  There was an improvement noted, but still a stinker.  Read up and decided to try ascorbic acid - made a stock solution and added to 35ppm - will leave for a week and then hit with Reduless again and see what happens. 

3rd batch was the worst - my nose responded with righteous indignation taking a whiff.  Used Kupzit for this one and let sit a week.  Again, some improvement, but in the end, still offensive.  35ppm ascorbic acid here as well and I think will try Kupzit again.

Jay, to answer your question, no - I didn't test for disulfides - I found this article under after I started the process: https://midwestwinepress.com/2014/11/01/back-basics-preventing-rotten-eggs-aka-reduction/  Many of you probably know this chemistry a lot better than I do, but I found it to be a good primer and the table near the bottom of the article with the decision matrix is handy.  If I had to do over again, I'd trial a small volume first and then treat the entire batch once I had the correct approach dialed in. 

Moving forward, I'm doing my best to be diligent to play prevent defense and keep the VSC (H2S) development at bay during primary fermentation when it's a bit easier to do something about it.  The article mentions splash racking and I had a mind to try force-carbonating with a carb stone and purging repeatedly (actually did try that, but after primary fermentation was done - I suspect disulfide compounds had already formed and weren't blowing off)

Good luck, Jay!

Best,

Brian

OOLLC

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