Portobello mushrooms, also known as portobella mushrooms and crimini mushrooms, or by their scientific name, Agaricus bisporus, are one of the most widely distributed mushrooms, found in every continent and almost every climate. These mushrooms are easy to identify because of their large size, which is at least four inches (about 10 cm) in diameter, and their characteristic brownish color. They also have a deep musty smell that makes it seem like they were just picked up from the forest.
These mushrooms are white and rounded when young, and may be called crimini or baby bellas. As they mature, the cap of the mushroom becomes flat and acquires their distinguishing dark color. They are mostly eaten broiled and grilled, but they can also be fried, baked, or sautéed. Because of their size and format, they are often used as a replacement for hamburgers in vegetarian recipes. Portobello mushrooms have a characteristic meaty texture that gets better the longer the mushrooms are cooked, so grilling may be the best way to bring out the flavor.
When buying portobello mushrooms it's important to avoid any that look broken or bruised, as this may contribute to loss of flavor. They are especially sensitive to air oxidation, so they should be stored wrapped in a paper towel or in their original container. Refrigerating portobello mushrooms is OK, but the longer they're kept, the more they tend to lose their flavor — these mushrooms should ideally be consumed within five days of purchase. Avoid washing portobello mushrooms before cooking, as this also may contribute to loss of flavor. Tapping them to remove excess sand or debris is enough, or sweep them lightly with a cooking brush.