Excerpt: Sweet Potatoes

the appetizer:

The Science of Good Food by Andrew Schloss and David Joachim explains the mysteries of food and cooking. Check out topics like Caviar; Extracts; and Sweet Potatoes; plus recipes, including Acorn Squash Filled with Pumpkin Seed Risotto and Roasted Root Vegetables.

Cookbook

Sweet Potatoes

What It Is

Sweet potatoes are not potatoes. Both are New World vegetables but they are from different botanical families. They aren't even the same type of vegetable. Potatoes are tubers (underground stems). Sweet potatoes are roots—specifically the root of a morning glory.

Crew members on Columbus's first trip to the Americas were the first Europeans to taste a sweet potato. They called it by its Haitian name, batata. Later European explorers started calling the white potato batata, leading to centuries of confusion.

The sweet potato is native to Peru, where it was cultivated before the time of the Incas. By the 13th century, it was a staple food in Central America and the Caribbean, and there is evidence that it traveled as far west as New Zealand before the Europeans ever came to the New World. Other stories attribute its movement into Asia via Europeans at the end of the 15th century. Regardless of how it got there, the sweet potato is wildly popular in Asia. Roasted sweet potatoes are sold by vendors on the streets in China and Japan, and China is the largest world producer.

It was likely slave traders who took sweet potatoes to Africa, where it was compared to a native tuber, the nyam or igname. Since then the sweet potato has grown in popularity in Africa, and the name yam has become identified with orange-fleshed sweet potatoes in North America even though the true yam is from another plant species.

What It Does

Most sweet potatoes are eaten fresh, usually baked in their jackets or boiled and mashed. They are also fried as chips or wedges, and in many recipes they are candied, underscoring their natural sweetness. Sweet potatoes are higher in starch and sugar than white potatoes and lower in protein. The orange-fleshed varieties supply a good amount of vitamin A in the form of beta-carotene (one roasted medium sweet potato contains two to three times the daily value of vitamin A).

There are two types of sweet potatoes: soft and firm. Orange-fleshed sweet potatoes are of the soft type, which tend to be sweet and moist. Firm-type sweet potatoes have dry, mealy flesh when baked, and their flesh is usually white or pale yellow.

How It Works

The sweetness of sweet potatoes is intensified by slow baking, thanks to an amylytic enzyme that breaks starch down into maltose (the same sugar that makes malted grain sweet). The action of the enzyme is greatest between the temperatures of 135 and 170°F (57 and 77°C). Slow baking therefore increases the sugar content of sweet potatoes far more than boiling or quick roasting.

Sweet potatoes are fairly perishable, and like most subtropical produce they are damaged when stored at temperatures below 50°F (lO°C). Chilling injury results in a syndrome known as hardcore, in which the center of a sweet potato remains hard even after prolonged cooking.

Fast Facts

Pale orange sweet potato noodles, made from sweet potato starch, are prized in Korea and Japan for their chewy texture.

Sweet potatoes from the New World arrived in Spain after Columbus's first voyage but didn't travel into the rest of Europe until Catherine of Aragon, Henry VIII's first wife, took them to England as part of her dowry. The king liked them so much that he offered a prize to any gardener who could grow them in England. By the mid-16th century, sweet potatoes blossomed allover England. But their popularity was short lived. Sweet potatoes cannot thrive in a cold climate; the crops soon withered and died.