Of Pith and Myth

By Robert L. Wolke
Wednesday, August 16, 2006

M any of my cookbooks recommend fresh citrus

zest as a flavoring agent. But they always caution against getting any of the white pith beneath it into the food. They say its bitterness will ruin the dish.

But my new Vita-Mix blender cookbook recommends grinding the pith -- along with the seeds and pulp -- into the smoothie or soup being prepared.

Both points of view can't be right. Is it possible that the bitterness of the pith is an urban myth? I'm told, for example, that the French eat rhubarb leaves, which American authorities say are poisonous. Has anyone ever tested that one, either?

I wish all urban myths were as easy as those to prove or disprove. I'll answer your question in three parts: the pith, the rhubarb and the Vita-Mix.

The Pith

An incorrigible experimenter, I personally carried out the appropriate scientific research to test the hypothesis of bitterness in the pith of citrus fruits. My experimental protocol was relatively straightforward: I tasted the stuff.

With a very sharp knife, I removed wide strips of colored zest (the fruit's exocarp) from four varieties of orange, two varieties of lemon and two varieties of grapefruit. (Limes, I found, have extremely thin layers of zest and pith -- too thin to separate.) I then pared a slice of pure white pith (the endocarp) from each fruit and submitted it to a panel of discriminating tasters (my wife and me) for sensory evaluation.

Results: The grapefruit piths were quite bitter, even leaving a lasting sting on the tongue; the lemon piths were only mildly bitter; and the orange piths were almost tasteless. All had a rather unpleasant, spongy chewiness.

Except for grapefruit, then, the "bitter pith" legend appears to have little basis in fact, especially for oranges. Is it possible that all citrus fruits have been tarred with the brush of bitterness because of an overexuberant generalization from grapefruit? Many food myths have flourished from roots less firmly anchored in fact.

My work was far from a definitive study, of course. As scientists often say when they want more funding, "further research is necessary."

But even if all citrus pith were indeed bitter-tasting, so what? Bits of pith might be visually unwelcome as white fragments in a dish that calls for the zest alone, but they certainly wouldn't ruin the dish's flavor. In fact, a touch of bitterness is a highly desirable component of what many regard as the three basic food groups: coffee, beer and chocolate.

The Rhubarb

I'd never heard that the French eat rhubarb leaves. But it is well known that they eat many things that would gross out most Americans, such as snails, frogs' legs, tripe, brains and -- also common in many other cultures -- horse.

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