The sweet potat(o) debate

I meant to write this post before Thanksgiving, but, well, you know, time getting away and all that. Then last week, following my On Nutrition column on “7 healthful foods for your holiday feast,” I received an email from a reader asking if there was a mistake with one of the photos that ran with the column in the print edition of The Seattle Times. The photo was labeled as sweet potatoes, but the reader thought the orange-fleshed tubers in the photo were clearly yams.

“Ah, yes,” I thought. “There is still a need for that post!”
Let me start with a bold statement: Unless you hail from Africa or shop for produce in international markets, you have probably never ever eaten a yam in your life.
The true yam (well, all 600+ varieties of yams) are not related botanically to sweet potatoes. (Yams are related to lilies and grasses; sweet potatoes are related to morning glories.) The true yam is native to Africa and Asia, and 95 percent of today’s yam crop is grown in Africa. Yams can range in size from that of a small potato to more than five feet in length. (In 1999, one record-breaking yam weighed in at 130 pounds.) Yams have a dark, almost bark-like skin, and can have white, purple or reddish flesh.
What we think of as yams in the United States are actually sweet potatoes. Yes they are. There are many varieties of sweet potatoes, just as there are many varieties of apples, oranges, grapes, squash, carrots, lettuce and so on. Most sweet potatoes are either creamy white (bordering on yellow), or orange/orange-red. There are purple sweet potatoes, too, although these are newer on the scene (2006) and less readily available. 
Some sweet potatoes are firm, others are soft. The firm ones, which stay firm after cooking, were the first varieties grown in the US, and tend to have pale flesh. The soft varieties, which also have orange or orange-red flesh, were later to the party, and producers decided to call them “yams” to distinguish them from the firm, pale, sweet potatoes that everyone was used to. In this, sweet potato producers took their cue from African slaves, who had already been calling these softer sweet potatoes “yams.” If you want to geek out, here’s a link to a 1918 treatise on sweet potatoes vs. yams.

According to the Library of Congress, today the U.S. Department of Agriculture requires that any sweet potatoes that have the term “yam” on the label to also have the term “sweet potato.” Despite this, the confusion persists. If you go looking for Thanksgiving recipes online, you will see as many references to “sweet potato casseroles” as you do “candied yams.” Both usually refer to the orange-fleshed sweet potatoes.
So there you have it! Now go forth and enjoy those orange-fleshed sweet potatoes, because they are delicious and supernutritious (yay for beta carotene)!
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