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Post by bunkie on Jul 26, 2014 11:39:23 GMT -5
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Post by kevin8715 on Jul 26, 2014 20:16:04 GMT -5
Sounds interesting. Now if I can only get oca to survive the summer here without drying out or rotting. Or a variety that is planted in the fall to be harvested in the spring would be great.
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Post by billw on Jul 26, 2014 22:35:39 GMT -5
It is tasty. I'm having another piece right now. If you try it, please let us know how it turns out.
I think there are probably a lot of possible uses for oca stems. Crisp and a little sour could pair well with a lot of things.
The only question is how much oxalic acid is in the stems. If I can find an extraction protocol for oxalic acid, I could work it out, but extraction of organic acids turns out to be surprisingly arcane.
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Post by Joseph Lofthouse on Jul 26, 2014 23:15:45 GMT -5
The only question is how much oxalic acid is in the stems. If I can find an extraction protocol for oxalic acid, I could work it out, but extraction of organic acids turns out to be surprisingly arcane. As the resident guru of arcane chemical knowledge... [ I had to look up the definition of arcane, but oxalate chemistry is straight forward.  ] Sodium oxalate is soluble in water but calcium oxalate is insoluble in water... Therefore the quick and dirty version is: Treat the plant material with soda or lye to convert the oxalate into sodium oxalate which is water soluble. Filter out the junk or let it settle.(discard the solids.) Add a concentrated solution of calcium chloride to the liquid and calcium oxalate will precipitate out of the solution. Discard the clear solution saving the solids. Dissolve the solids in dilute sulfuric acid which will precipitate out calcium sulfate leaving oxalic acid dissolved in solution. Discard the solids. Concentrate the solution by boiling until crystals start to form. Cool and save the crystals. |
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Post by billw on Jul 27, 2014 0:17:53 GMT -5
Thanks Joseph. Actually, the hard part isn't extracting the oxalate, but only the oxalate. There is a bunch of tartaric acid and malic acid as well. They'll also yield water soluble products that precipitate with calcium chloride, I think. So, it is going to be a multi-step process to separate out, which is where I got stuck last time. If you have any thoughts on how to work through that, advice would be most welcome.
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Post by kevin8715 on Jul 27, 2014 1:03:11 GMT -5
I imagine a variety can be bred to lower or maybe completely eliminate the oxalic acid (would that make the plant vulnerable to insects). Taste might be sufficient or isolating the oxalic acid to see the ratio of stem weight to oxalic acid weight.
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Post by Joseph Lofthouse on Jul 27, 2014 11:11:55 GMT -5
Malate can be separated from oxalate because malic acid is soluble in ether, but oxalic acid is only slightly soluble so rinsing the final acid crystals with ether would preferentially remove the malic acid. Also malic acid is highly soluble in water while oxalic acid is less soluble, so the malic acid will tend to stay in solution when the oxalic acid crystals form.
Tartrates can be separated from oxalates because sodium tatrate (or tartaric acid) is insoluble in ethanol while sodium oxalate (or oxalic acid) is soluble in ethanol.
So to modify the previous recipe...
Treat the plant material with soda or lye to convert the oxalate into sodium oxalate which is water soluble. Filter out the junk or let it settle.(Discard the solids.) Add a concentrated solution of calcium chloride to the liquid and calcium oxalate will precipitate out of the solution. Discard the clear solution saving the solids. Dissolve the solids in dilute sulfuric acid which will precipitate out calcium sulfate leaving oxalic acid dissolved in solution. Discard the solids. Concentrate the solution by boiling until crystals start to form. Cool and save the crystals. Rinse the crystals with ether to remove any malic acid residue. Dissolve the crystals in ethanol discarding any residual non-soluble (tartrate containing) solids. Boil off the alcohol to recover oxalic acid.
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Post by billw on Jul 27, 2014 18:01:02 GMT -5
Many thanks, Joseph! I'll give that a try.
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Post by raymondo on Jul 27, 2014 18:15:30 GMT -5
I can't grow oca tubers but the tops do okay here. Perhaps I could just use them for stems - the occasional oca pie sounds like a treat.
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Post by steev on Aug 13, 2014 20:07:27 GMT -5
Re-reading this thread, I wonder how many of us have access to an electronic scale sufficiently sensitive to really weigh the resultants? I have only a balance scale (of WWII vintage, according to the gummint sticker, not that I think actual weights have changed much in the last 70+ years). I think it's a cool decoration, and never use it to weigh out small quantities of anything, neither in metric nor English units. I miss access to serious lab-ware and equipage.
I wonder how the oxalis level in oca (stems) compares to that in the weed sorrel (sourgrass) endemic to California, which every kid chews the stems of at some point, given the opportunity, to no known deleterious affect.
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Post by hortusbrambonii on Aug 14, 2014 0:55:40 GMT -5
Oca-leaves and stems taste like Rumex-sorrels or rhubarb, both of with are liked because of their sour taste which seems to some from oxalic acid, or is there another acid that gives the taste in those?
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