At the bottom of my wine decanter (which due to its shape is fantastically hard to clean mechanically) a layer of reddish brown precipitate forms. I believe this is probably potassium bitartrate crystals, which are coloured reddish brown by the presence of tannins, which in essence is a polyphenol.

I would like to know whether there is a chemical that I could use to clean the decanter with minimum mechanical action. I have tried water (with and without soap), alcohol (in the form of vodka), isopropanol without success. I have yet to try acetone. Preferably the solvent should not be greatly toxic (at least I'd like to be able to wash it out with water and reuse the decanter), and not react with high lead-content glass (which is what decanters are made out of) - hydrofluoric acid is thus to be avoided (as usual). It is unsurprising alcohol doesn't work as the reason tartrates precipitate is apparently because they are not soluble in alcohol. It would also be useful if I could purchase the solvent outside a lab environment.

My understanding is that potassium bitartrate is more soluble in acid solutions. I've tried citric acid (made up from powder) and vinegar, but the effect if any is modest.

I don't much care if the method used is to react with (rather than dissolve) the precipitate.

(Note this question is in part a thought experiment. I realise that in fact the best way to clean decanters is generally mechanical despite the difficulties, and I'm familiar with the copper beads method and the egg-shell method, as well as no end of sponges on bendy sticks. However, I'd like to know whether there is a chemical way. Also note that I added an 'equipment' tag as it's possible that some know-how from cleaning chemistry glassware might be useful here)

  • $\begingroup$ Strong cleaning solutions of an acid and an oxidizer which would be used in a chemistry lab are not suitable for home use. It wouldn't be safe for you or your drains. $\endgroup$ – MaxW Sep 27 '16 at 17:26
  • $\begingroup$ Do you have a water pick for dental cleaning? I'd think that a well aim blast would dislodge the crud. $\endgroup$ – MaxW Sep 27 '16 at 17:30
  • $\begingroup$ @MaxW No I don't. In this particular decanter the neck is narrow, and the crud sticks in a place where there is no straight line exit via the neck - not sure a pick would reach it. In any case I'm trying to find a chemical solution (preferably one safe for me and my drains too). $\endgroup$ – abligh Sep 27 '16 at 17:44
  • $\begingroup$ Did you try a dishwasher soap in warm water? $\endgroup$ – MaxW Sep 27 '16 at 17:59
  • $\begingroup$ @MaxW I've tried hot soapy water (obviously) and washing-up liquid. Dishwasher soap (i.e. for machines) is not recommended for decanters of this sort as it is too abrasive and can scratch the glass and make it opaque. The best current method I have involves sponges on bendy sticks, soapy water and washing up liquid, but to repeat this isn't a 'how do I clean my decanter' question, it's a 'what chemicals could I use to attack/dissolve the precipitate' question. $\endgroup$ – abligh Sep 27 '16 at 18:33

The CRC Handbook indicates that potassium d-tartrate and dl-tartrate are soluble to the extent of 100-150 grams per 100 mL H2O vs about 0.5 grams for the bitartrate. Rather than using acid to clean the decanter, alkali would neutralize the bitartrate to the much more soluble tartrate . Washing soda (Na2CO3) should not be too alkaline, but even sodium bicarbonate (NaHCO3) might work. Neither is expected to be harmful at the level that might exist after rinsing.

The tannins or other organic might slow things down. Bleach (NaClO) is alkaline, and although bleach is toxic if ingested, it should present no problem if the decanter is rinsed. Water could be flushed around inside the decanter, then tested with litmus paper. Or the decanter could be rinsed with vinegar and a little honey to remove the bleach: the vinegar makes the liquid acidic (HClO) and the honey gets oxidized to gluconic acid, consuming all the bleach - leaving a sweet, tart taste.

  • $\begingroup$ Really interesting. I'd tried baking soda (did not seem to help much), but not washing soda. Slightly fearful of bleach in case it leaches (somehow) into the glass or the scratches in it (in seems quite soft), but I can't immediately think how bleach would do that. Perhaps I should pluck up the courage to try this. $\endgroup$ – abligh Feb 16 '18 at 10:04

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