Sweet Potato

Not the same as a yam

In American supermarkets, “yam” is often a misleading label for orange-fleshed sweet potatoes. True yams are an entirely different plant — Dioscorea, a different family — native to Africa and Asia, with rough bark-like skin, drier flesh, and far less sugar. The U.S. agricultural confusion dates from the 1930s, when sweet potato marketers wanted to distinguish the new orange varieties from the older white “sweet potato”; they borrowed the African word “yam” (from the Wolof nyami). The label stuck, but it’s wrong.

Not a potato either

Despite the name, sweet potatoes are not potatoes — different family entirely. Common potatoes are Solanum (nightshades, like tomatoes and eggplants); sweet potatoes are Ipomoea (morning glories). Their starches behave differently in cooking, their nutrition is different, and they descended from different wild ancestors.

Why orange flesh?

The orange color comes from beta-carotene — the same provitamin A pigment that colors carrots. White-fleshed sweet potatoes (the older varieties, still common outside the U.S.) have far less beta-carotene. Public health programs in vitamin A-deficient regions have specifically introduced orange sweet potato varieties because of their nutritional value; programs in sub-Saharan Africa have measurably reduced childhood blindness.

Curing

Freshly-dug sweet potatoes are starchy and bland. Curing at warm humid conditions (29 °C, 90% humidity) for 4–7 days converts starches to sugars and toughens the skin for storage. After curing, sweet potatoes can keep for months at cool room temperature, growing sweeter as they age.

The bin of “fresh” sweet potatoes at the supermarket has typically been cured for several weeks; this is why supermarket sweet potatoes taste sweeter than ones dug from a backyard garden a day prior.

A global staple

Sweet potato is the sixth-most-important food crop in the world by total tonnage. China alone produces over 70% of the global crop, mostly for animal feed and starch processing. In African and Pacific cuisines, sweet potatoes are a primary carbohydrate (Ugandan posho, Tongan kumala, Filipino kamote).

Stokes Purple and other purple varieties have higher anthocyanin content, the same antioxidant family in blueberries — making them subjects of nutrition research and trendy ingredients in modern restaurants.