What Are Nightshades?

You may have heard the term nightshades as it relates to certain foods and wondered what it means. It certainly has some ominous overtones, especially as it tends to bring to mind the so-called "deadly nightshade" (which, thankfully, isn't a food at all). So what are nightshades, and what role do they play in your cooking?

What Are Nightshades?

Nightshades are a family of flowering plants, classified as Solanaceae, comprising more than 2,700 species. This includes four that are of interest from a culinary standpoint: potatoes, eggplant, tomatoes, and peppers. 

For those who like to geek out on botanical names, potatoes, tomatoes and eggplant are classified under the genus Solanum, while peppers are classified under the genus Capsicum. For instance, potatoes are known as Solanum tuberosum, tomatoes are Solanum lycopersicum, and eggplant are Solanum melongena. Peppers, however, are known as Capsicum annuum since they are classified under a different genus, although all four are members of the Solanaceae family.

While potatoes are vegetables since they are an edible root, the other three—peppers, eggplant, and tomatoes—are all fruits. This is because they have seeds, and the definition of a fruit is any part of a plant that bears seeds.

As for the so-called "deadly nightshade," this term refers to Atropa belladonna, sometimes referred to simply as belladonna. This plant has poisonous leaves and berries whose only relation to potatoes, eggplant, tomatoes, and peppers is that it comes from the Solanaceae family. 

Potatoes

Potatoes are among the most versatile foods in the world and are commonly prepared using every cooking technique, including frying, boiling, steaming, roasting, baking, and sauteeing. They're available in numerous varieties in a range of starchiness, with russet potatoes, which most people know of as the standard brown baking potato, being the starchiest. In addition to baking, russets are great for making mashed potatoes and french fries. 

Yukon golds are a wonderful all-purpose potato with medium starch that are equally good for mashing, baking, boiling, and roasting. White and red potatoes are known as waxy potatoes because their texture is much firmer and less mealy than russets. Waxy potatoes are excellent for roasting, boiling, and in soups and stews since they hold their shape and don't fall apart.

Tomatoes

You might not be able to make them into french fries, but tomatoes are every bit as versatile and ubiquitous as potatoes. They appear in cuisines from the Americas (where they originated) to Europe and Africa and, to a lesser extent, Asia, where they were introduced by the Spanish in the Philippines and eventually made their way across Asia.

Unlike potatoes, which are really only eaten cooked, tomatoes can be eaten cooked or raw. Indeed, while they can be stewed and made into sauces, one of the best ways to enjoy tomatoes, especially the super-flavorful heirloom varieties, is in salads and sandwiches. 

Eggplant

Eggplant grows in all kinds of shapes, sizes, and colors, ranging from small two-inch globes to oblong and tubular varietals that can surpass 12 inches in length. In the U.S., the most common variety is the Italian eggplant, recognized by its glossy, purplish-black skin and creamy white flesh. Common methods for cooking eggplant include frying, sauteeing, steaming, simmering, grilling, and roasting. It is usually sliced or diced and can be prepared with its skin on or off.

In addition to the Italian variety, the Japanese or Chinese eggplant is much longer and narrower and features a lighter purple and white skin.

Peppers

Peppers, a species that includes sweet varieties like bell peppers to the ultra-hot habanero and scotch bonnet varieties, are most notable for the fact that they contain a chemical compound called capsaicin which results in the sensation of pungency, or spiciness. The bell pepper is the only exception to this since they don't produce capsaicin at all. 

The hotness of chiles is measured according to the Scoville heat scale which assigns a score to each chile in Scoville heat units. So that for instance, bell peppers are 0, Anaheim peppers are 500 to 1,000, jalapenos score 2,500 to 8,000, and habaneros are at 80,000 units and sometimes much higher.

What Is Not a Nightshade?

At least two foods are sometimes erroneously grouped in with nightshades: zucchini and okra. Zucchini are from the family Cucurbitaceae, in the genus Cucurbita, which also includes squash and pumpkins. Okra are from the family Malvaceae and the genus Abelmoschus, of which okra is the primary edible species. And this is where those botanical names come in handy. Because if it's not in the family Solanaceae, it's not a nightshade.