Agaricus bisporus is usually called the common or commercial mushroom. If you’re looking at mushrooms in the store with the white cap, you’re very likely looking at varieties of A. bisporus. This species of mushroom may be sold under many different names, which may denote size. Small white versions of A. bisporus are generally referred to as button mushrooms, while larger versions may have the generic name of mushroom.

True button mushrooms are picked when they are very young and when the caps of the mushroom are still closed. They should be free of any marks or discolorations, and the stems on the bottoms of the mushrooms should not have hardened. Generally when you get fresher mushrooms, they are easy to slice and the whole mushroom, stem included, can be used. Those that have sat for a few days in the grocery store, or that are larger may feature a hardened bottom stem that needs to be removed prior to slicing or preparing the mushroom.

Button mushrooms tend to refer to a specific size but they are not the only mushrooms that are A. bisporus. For instance, Portobello mushrooms are merely large, brown versions of the button mushroom, as are smaller Italian brown mushrooms. You might also find wild mushrooms in button size, simply meaning they’re smaller and picked at an earlier stage.

Many people prefer smaller versions of A. bisporus because they tend to be freshest and are most likely to feature the closed cap. A closed cap means that you can’t see the tiny black fibers inside the mushroom when you turn it upside down. Avoid open cap button mushrooms as these are of inferior quality.

When preparing button mushrooms, most chefs suggest merely wiping off the mushroom to remove any dirt. You can wash them too, but they are porous and likely to absorb liquids. If you do plan to wash, not a bad idea considering many mushrooms are grown in manure, do so right before you plan to serve or cook them. Though you can purchase sliced mushrooms at the store, most chefs suggest slicing your own to get the freshest tasting button mushrooms. Also, if you are concerned about the dirt in which they’re grown, it’s challenging to wash pre-sliced mushrooms.

You can find button varieties in the canned food section. Some are pickled or packed in oil and vinegar. They make great toppings for individual pizzas because of their convenient size, and are an excellent addition to stir-fried dishes and salads. With all mushroom sizes or ages you do need to be careful not to overcook the mushrooms, or they can get rubbery and slimy. If you’re adding mushrooms to a stew for instance, wait until the last five to ten minutes of cooking prior to adding them.

If you’re a mushroom enthusiast, you can find button mushrooms in the wild, but they can easily be confused with A. Californicus, a look-alike that is mildly toxic. These two species truly look alike, so gathering wild button mushrooms should only be done with an expert on these fungi.