Deep-fried mushrooms are any of the many edible varieties of mushrooms that have been coated in flour or batter and cooked in hot oil until the coating is crisp and the mushrooms have lost some of their moisture and become just slightly dense. Such mushrooms are popular as an appetizer and as part of a larger meal or salad. They are frequently served with some type of dipping sauce that can be heavy with ingredients such as horseradish or mayonnaise. The coating on the outside of deep-fried mushrooms can be a light dusting of flour or it can be a tempura or beer-based batter that has been allowed to rest for some time before use. For most recipes, white button mushrooms are called for, although nearly anything from older cremini mushrooms to shitake or chopped oyster mushrooms can used.
The mushrooms are prepared for deep-frying through vigorous cleaning to remove any dirt or other particles, especially from the gills under the cap. The stems do not have to be removed, although many chefs cut them down to match the base of the cap to create a solid, compact shape. Recipes sometimes call for the gills to be removed from the cap, although this is mostly an aesthetic choice and will not make much difference with deep-fried mushrooms, unless more space is required for breading.
The batter used for deep-frying mushrooms varies from one recipe to the next. The most basic version involves just flour, eggs and water that are mixed together until well blended. Beer is sometimes used to add extra crispness. Lighter coatings can be made by increasing the amount of water for an airy tempura-like texture. Other ingredients can include breadcrumbs, cornmeal, crushed corn flakes and spices such as cayenne pepper.
Once the mushrooms have been dipped into the batter, they can be allowed to rest for a few minutes on a baking pan so excess batter rolls off the surface and the batter dries just a bit. The oil being used for deep-fried mushrooms needs to be within the 350° Fahrenheit to 375° F (about 176° Celsius to 190° C) range that it will cook the batter. As each batch is added, the temperature is monitored, because cooking too many deep-fried mushrooms at once could bring the oil temperature down too far.
After drying on a paper towel when they have finished cooking, deep-fried mushrooms can be served. When used as a snack or appetizer, they can be accompanied by sauces such as marinara, Russian or ranch dressing, or horseradish dip. The mushrooms can be sliced or added whole to a green salad or they can be used with other deep-fried ingredients, such as deep-fried mussels, oysters or vegetables.