I recently crushed and strained about thirty pounds of wild grapes to ferment into wine. About a month in, I did a visual inspection of the wine under microscope to try and identify some yeast and bacteria species. However I was more taken by the sight of many sharp, needle-shaped crystals in the wine (along with microbes). Pictures are below:

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My best guess is that they are raphides (crystals of calcium oxalate/carbonate), a supposed defense mechanism of some plants. These seem to be complicit in causing acridity in certain plants, and indeed the grapes (and resultant wine) were extremely tart. I've not, however, heard of any wild grape species having known toxicity.

My question is, then: are any wild grape species known to produce such crystals and, if so, are they known to be harmful in any way? Is there another explanation?

  • $\begingroup$ They certainly do look like calcium oxalate crystals! $\endgroup$ – TanMath Nov 1 '15 at 20:57
  • $\begingroup$ You just reproduced some of Louis Pasteur's work. en.wikipedia.org/wiki/Louis_Pasteur#Molecular_asymmetry $\endgroup$ – AMR Nov 1 '15 at 23:42
  • $\begingroup$ Try here. awri.com.au/industry_support/winemaking_resources/… $\endgroup$ – AMR Nov 1 '15 at 23:49
  • $\begingroup$ If they are really oxalate crystals, the harm depends on the concentration. Some ppl are on oxalate diet, because they would develop gallstones or kidney stones otherwise. It is not considered toxic, you can drink it. $\endgroup$ – inf3rno Nov 2 '15 at 19:03

you are correct that these grapes have raphides. After doing some research, I found out that the grape raphides are twinned crystals. Raphides can cause much irritation for many herbivores (therefore, it is a protection mechanism) but less so for humans. In grapes, however, the irritation is much less than other raphide-containing species. This probably has to do eith the fact that it has a twinned structure (this is what I think, but I haven't found any research on this).

As a side note, what you have done is known as a whole mount, in which is entire organism specimen is placed on the slide, usually after crushing. It is a geeat way to examine the contents of the cell vacuole, which is where this raphides are commonly found.


  1. http://www.ncbi.nlm.nih.gov/pubmed/10648203

  2. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0091341

  • $\begingroup$ You should add some references. :-) $\endgroup$ – inf3rno Nov 2 '15 at 19:00
  • $\begingroup$ @inf3rno I have added references $\endgroup$ – TanMath Nov 2 '15 at 20:47

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