Last weekend while finishing up a dinner party with some lovely strawberry-rhubarb pie, a friend asked, “Why can I eat rhubarb stems but not the leaves?” Well...I was stumped…but the question made me curious enough to drive me to the PC after the party broke up (with another slice of pie in hand, of course). It turns out that rhubarb leaves and stems both contain oxalic acid. The leaves have a higher concentration of the acid than the stems. Apparently, we have several metal ions in our body that perform important functions. Oxalic acid combines with these metals and removes them from our systems. Most notable of these vital metals is calcium. (Calcium is an alkaline earth metal – yet another learning from my friend’s question.)
Investigating this question led to other random information about oxalic acid and rhubarb I thought you’d enjoy:
- Turns out that rhubarb is a mild laxative (our body’s way of clearing out this toxin before too much can be absorbed).
- Many plants contain oxalic acid such as spinach, black pepper, tomatoes, cabbage, and chocolate.
- Oxalic acid is used by plants to keep insects from eating the fruit until it’s ready to drop. (So, not only are vine ripened tomatoes better tasting, the fruit is much less likely to still contain oxalic acid).
- Calcium oxalate (oxalic acid + calcium) turns into crystals. If these crystals grow large, they can block the tubules in the kidneys (calcium oxalate is found in kidney stones).
- If you drink a glass of milk while eating rhubarb (or spinach) you get a “gritty feel” in your mouth. That “grit” is the calcium oxalate that has formed.
Want to know about oxalic acid? Check out this Web site:
everyday-chemistry.suite101.com/article.cfm/rhubarb_and_other_poisons.
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