Alton Brown discuses the difference between sweet potatoes and yams with nutritional anthropologist Deb Duchon. It turns out sweet potatoes are not merely potatoes that happen to be sweet. They are actually a root of a vine in the morning glory family. Deb explains how the roots that Christopher Columbus brought back to Spain in 1493 were called "batatas" by the Indians who lived in the Greater Antilles Islands. In Spain they called them "patatas." The Spanish introduced them to the English by serving a sweet potato pie to King Henry VIII, who was so grateful he took it back to England, where they mangled the name to "potatoes." The "sweet" wasn't added for 200 more years when Irish immigrants started arriving in Boston with white potatoes. In the 1930s some Louisiana farmers developed an orange variety of sweet potato, which they wanted to differentiate from the yellow variety that then dominated the market. At that time "yam" was already Southern slang for sweet potato, as slaves who had come from West Africa compared them to the yams they had grown back home. Sweet potatoes are available year-round, but their flavor peaks in the fall and winter. Alton recommends choosing specimens that are heavy for their size and free of any soft spots or sprouts. As sweet potatoes are harvested when they're really moist, they are then cured, or partially dried, in kilns to toughen the skin and increase their storage potential. They should be kept in dry, cool and well-ventilated areas and used within 10 to 15 days. They also bruise easily, so be sure to be gentle with them.