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Accumulation of Silver Metallic Residue in Rye Stripping Operation
Hi, we have a pot still and are distilling on the grain and we’ve noticed a silver metallic build-up that will occur after just one run of our 250 gal still. Does anyone have any experience with this? Otherwise the quality of the spirit seems good, but because our still is 1/2 the size of our fermenters it would be ideal if we could prevent this so we don’t have to break down and clean between every stripping run. Other spirits (apple brandy and gin) have been run through with no similar problems.
I’ve attached a picture of the lyne arm after a single run. We suspect there may have been some carry over, but we know there was none in the second run and we had the same problem, despite a thorough cleaning of the still.
Thanks,
Eli
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14 Replies
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I dont have a good answer but did some searching and found another guy that seems to have had a similar issue. There are a few suggestions in this thread but no clearly identified cause:
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It may be Copper Sulphide. our first still would have the same silver buildup in the lowest plate. it was a Chinese still and the copper seemed to have a touch of bronze or brass in it. our current still never presents a copper salt in silver (always black) and it is german copper. don’t know if any of this is applicable or if it helps. but it does look familiar.
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How is your kettle heated?
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We have a steam boiler and internal coils. Does not appear to be scorching, though there does appear to be scale forming after a single run. We’re currently looking into our water treatment and enzyme dosage as starting points.
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Have the metallization tested to determine what it is. Quick test is just determine what it is soluble in. If it is metal, it will be insoluble in water. If it is a soluble in water, metal salt. If not, but soluble in alcohol, organic salt. Etc. You might want to do something like atomic emission spectroscopy, which gives you the elemental analysis. That will tell you if you have a salt or metal, and if it is copper salt or something far worse, like poor joint materials or alloys.
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We’ve experienced this in our pot still as well. We determined it to be some form of manganese. Have your water treated to rule that out. I think we assumed it came from some sort of fertilizer used on the grain? Not 100% sure.
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What was the manganese theory based on? There were some other similar threads across the web (so this is less unique than you might think) and I’d always thought it was some kind of zinc complex.
Copper, Iron, Manganese, and Zinc are typically found in distillery wastewater effluent.
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Are you using a foam inhibitor in your ferment? Ferm-cap and other similar anti foaming agents can cause a metalic looking coat on your copper.
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We are using Foamsol-30 at a rate of 5 ml/hL in the fermenter and 10ml/hL in the still. Does anyone have a recommended dosing rate besides this one (this is what is recommended for brew kettles). As an update, we also lowered the amount of grain we were using per batch and that seemed to have a positive effect-we made it through 2 stripping runs and there was only a slight residue, and the spirit run was great. I think it was mostly the sulfur compounds in the grain since we are distilling on grain, but the ferm-cap also makes sense. Thanks for all the insights.
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Another thread discussing anti-foam http://adiforums.com/index.php?showtopic=37&hl=%2Banti+%2Bfoam#entry89 this thread sights some CFRs related to the use of chemicals in fermcap , I believe the same active chems as what you are using. My understanding is that fermcap is great for beer because it all settles out in the yeast/trub and is left behind when you rack off, not usually so in distilling. That being said I know a lot of people use it in distilling, but natural soap or oil might be a better option.
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I have the exact same thing happen in my still any time I do grain in distillations. The inside of my lyne arm looks identical to that. My still is a stainless steel pot made from a square tote tank. It has steam jacketing on all four sides. During the course of the run, the liquid level inside the still drops obviously, but because the steam jacket goes to the top of all four sides, there is a portion of the side wall that remains heated above the level of the liquid. After a run, it isn’t scorched, but there is a baked on caramelized ring around on the inside of the pot. During stripping runs, my output is pretty oily over the course of the entire run, but gets noticeably more oily toward the end of a run. Based on the solubility tests described earlier, would that mean it is some type of organic salt? That might make sense because the proof decreases over the run so whatever it is becomes less and less soluble over the run. I don’t use any type of anti foaming ingredients. My recipes are either 100% ground corn converted with SebStarHTL and SebAmylGL, or bourbon made from ground corn, barley, and wheat, with addition of enzymes as well. I’d love to hear any other theories anybody might have.Â
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I have had this happen to a test still of mine. Â I was distilling wheat grain in direct fire. Â Kettle was stainless steal, but I had copper mesh scrubbers for packing. Â The bottom of the first scrubber was covered in a silver looking metal liquid.
I am going with Glowe8 ‘s theory. Â I looked up copper sulphide and it looks to be exactly what I experienced(picuture and link below). Â I know there is no way to know for sure unless it is tested. Â But I am thinking one of the reasons we use copper stills is to remove sulphur compounds. Â So it would make sense that it is a sulphur based compound. Â Anyhow that is just my thought, let us know if you get it tested.
https://en.wikipedia.org/wiki/Copper_extraction_techniques
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I’m going to throw another question out there.  Is it common for a somewhat heavy element with a high boiling point to be carried up with the distillate??  Manganese has an atomic number of 25, sulphur is 16 both have boiling points well beyond the boiling point of water.  Trying to understand the concept here, are they just some how attached to the water and alcohol molecules and are carried up with them? Or are they part of another compound with a much lower boiling point?
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We’re not talking about vaporizing sulfur, but compounds in the wash that happen to have sulfur molecules attached.
DMS – Dimethyl Sulfide, DMDS – Dimethyl Disulfide, DMTS – Dimethyl Trisulfide, and a few others in lower quantity.  These are all formed during fermentation.
These are all commonly found in distilled spirits, finding the source of the sulfur is the easy part.
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Here is an oldie but goodie if you want to explore a bit:
The Impact of Copper in Different Parts of Malt Whisky Pot Stills on New Make Spirit Composition and Aroma
Barry Harrison*, Olivier Fagnen, Frances Jack and James Brosnan
ABSTRACT
J. Inst. Brew. 117(1), 106–112, 2011Â
In Scotch malt whisky production, the use of copper for the construction of the pot stills for distillation is regarded as having an important effect on whisky aroma. During distillation in cop- per pot stills, the copper acts to reduce sulphury aromas in the resultant spirit by reducing the levels of sulphur compounds such as dimethyl trisulphide (DMTS). This work has shown that the copper is more effective in this role in some parts of the pot stills than others. This information can be used to help distillers maintain or, indeed, to alter new make spirit aroma. It was also noted that in addition to DMTS, other, as yet unidentified, com- pounds make a significant contribution to sulphury aromas, so future research efforts should focus on identifying such com- pounds.Â
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