What Are Button Mushrooms

Introduction

Button mushrooms are the mushrooms most shoppers meet first. They sit in small boxes in the produce section, pale and round, with smooth caps and short stems. They turn up in salads, soups, pasta sauces, omelets, and stir fries, and they ask for little in return. A reader who has ever wondered what exactly is in that box, why the same mushroom also appears under the names cremini and portobello, or how such a plain looking fungus became a kitchen staple will find the answers here.

This guide explains what a button mushroom is in plain language, starting with its scientific identity and working through its appearance, its history, how growers produce it, how to use it in the kitchen, and what it contains nutritionally. It also explains what button mushrooms are not. They are not a separate species from cremini and portobello mushrooms, they are not wild mushrooms gathered from a field, and the cultivated mushrooms sold in stores are not the same thing as the mushrooms that appear in a lawn. For the parts of a mushroom in detail, see Parts of a Mushroom, and for the mushrooms that appear outdoors without being planted, see Mushrooms Growing in Lawn.

One Species, Three Familiar Names

The single most useful fact about button mushrooms is that the button, cremini, and portobello mushrooms in a grocery store are the same species. Agaricus bisporus has two color states while it is still young, white and brown, and each state carries several market names. When the white form is picked young, with its cap still closed, it is sold as a button mushroom, a white mushroom, a common mushroom, a cultivated mushroom, a table mushroom, or a champignon de Paris. When the brown form is picked young, it is sold as a cremini, also spelled crimini, a chestnut mushroom, a Swiss brown mushroom, a Roman brown mushroom, an Italian brown mushroom, or a baby bella. When the brown form is left to grow until its cap opens flat and measures about 10 to 15 centimeters across, it is sold as a portobello, also spelled portabella or portobella.

The differences between the three are a matter of strain and timing, not of species. The white strain gives the pale button mushroom. The brown strain gives the cremini when young and the portobello when mature. Flavor follows the same pattern. The button mushroom is the mildest of the three, with a gentle earthy taste and a firm, slightly crisp texture when raw. The cremini is a little firmer and a little deeper in flavor. The portobello is the most savory and meaty of the three, with a broad flat cap that holds up to grilling and stuffing. A cook who understands this can substitute with confidence, because the three behave the same way in a pan and differ mainly in intensity and size.

The name button comes from the shape of the young cap. Before it opens, the cap is a smooth, rounded dome that looks like a small button sitting on a short stem. The name has stuck because it describes exactly what a shopper sees: a neat, pale, button shaped cap that has not yet flattened or opened to show the gills beneath it. The scientific name carries its own story. Agaricus is the genus, a large group of mushrooms that includes both edible and poisonous species. The species name bisporus refers to the two spored basidia, the tiny club shaped cells that produce the spores, which set this species apart from related four spored forms.

This shared identity also explains why the three names are sometimes confused in recipes and in conversation. A recipe that calls for cremini mushrooms will work with button mushrooms, and a recipe that calls for portobello caps can use large button mushrooms in a smaller portion, but the results will be milder. The reverse is also true. A dish built around the deep flavor of a portobello will taste lighter if button mushrooms are used instead. The choice is a matter of flavor and size, not of a different ingredient altogether.

Where Button Mushrooms Come From

Agaricus bisporus is native to grasslands in Eurasia and North America, where it grows in rich soil, compost, and manure. In the wild it is a saprotroph, which means it feeds by breaking down dead organic matter rather than by living on a host plant. That habit is the reason it took so well to cultivation. Give it a bed of composted organic matter in a cool, damp, dark place, and the fungus will do what it has always done in a meadow, only on a schedule a grower can plan around.

The history of growing this mushroom stretches back further than most kitchen ingredients. The earliest scientific description of its commercial cultivation was made by the French botanist Joseph Pitton de Tournefort in 1707. Early growers watched for good flushes of mushrooms in fields, dug up the mycelium, and replanted it in beds of composted manure, but the method was unreliable, and spawn collected in this way often carried disease. A lasting improvement came in 1893, when sterilized pure culture spawn was produced by the Pasteur Institute in Paris for cultivation on composted horse manure. Pure spawn meant growers could start a crop from a clean culture instead of from a field sample, and commercial mushroom growing became a repeatable craft.

The white button mushroom itself arrived by accident. Modern commercial varieties of the common mushroom were originally light brown. In 1925, a white mushroom was found growing among a bed of brown mushrooms at the Keystone Mushroom Farm in Coatesville, Pennsylvania. Louis Ferdinand Lambert, the farm owner and a mycologist by training, took the white mushroom back to his laboratory, and cultures were grown from the mutant individuals. The pale mushroom was seen as a more attractive food item, much as white bread had been, and it became the standard. Most cream colored store mushrooms sold today descend from that 1925 chance mutation.

The scientific name took almost as long to settle as the crop itself. The common mushroom was first described by the English botanist Mordecai Cubitt Cooke in his 1871 Handbook of British Fungi, as a variety of Agaricus campestris. The Danish mycologist Jakob Emanuel Lange reviewed a cultivar specimen and named it Psalliota hortensis var. bispora in 1926. It was promoted to species status and renamed Psalliota bispora in 1938. Emil Imbach gave the species its current scientific name, Agaricus bisporus, in 1946, after the genus Psalliota was renamed to Agaricus.

Today the mushroom is grown on a scale that matches its long history. It is cultivated in more than 70 countries, and it is one of the most commonly and widely consumed mushrooms in the world. World production of mushrooms, including truffles, reached 48 million tonnes in 2022, led by China with 94 percent of the total, with Japan and the United States as secondary producers. Those figures cover all mushrooms and truffles, not button mushrooms alone, but they show how large the cultivated mushroom trade has become since a French botanist first described it in 1707.

How to Recognize a Button Mushroom

A button mushroom in a store is easy to recognize, and the features that mark it are the same features that define the species. The cap of the wild species is a pale gray brown, with broad, flat scales on a paler background, and it is first hemispherical before flattening out with maturity, typically measuring 5 to 10 centimeters across. The cultivated white form is smoother and paler, with a clean white to cream cap that is usually about 2.5 to 5 centimeters across when sold as a button mushroom. The cap is closed or only slightly open, and the stem is short and sturdy.

Under the cap sit the gills, thin plates that run from the stem toward the edge of the cap. In a young button mushroom the gills are hidden by the closed cap, but as the cap opens they show, first pink, then red brown, and finally dark brown with a whitish edge. The gills are free, which means they do not attach to the stem. The stem, called the stipe, is cylindrical, up to about 6 centimeters tall and 1 to 2 centimeters wide in the wild species, and it carries a thick, narrow ring, the remnant of the partial veil that once covered the young gills. The flesh is firm and white, and it stains a pale pinkish red when bruised. The spore print, the pattern of spores left when a cap is placed gill side down on paper, is dark brown. For a closer look at each of these parts and what it does, see Parts of a Mushroom.

That description also explains how a button mushroom changes as it ages. The cap starts as a closed dome and flattens as it matures. The gills darken from pink to brown as the spores ripen. The stem stays short relative to the cap. A mushroom sold as a button is picked before any of that has gone far, which is why the cap is closed, the gills are hidden or only faintly pink, and the flavor is mild.

A word of caution belongs here, and it is a firm one. Several wild mushrooms can look similar to Agaricus bisporus, and some of them are poisonous. The death cap, Amanita phalloides, which is extremely toxic, has been mistaken for Agaricus bisporus, and the poisonous European species Entoloma sinuatum has a passing resemblance. Young specimens of the lethal destroying angels in the Amanita genus can also be confused with the common mushroom, though they can be distinguished by the cup, called a volva, at the base of the stem and by their pure white gills, where Agaricus bisporus has pinkish or brown gills. A more common mistake is to confuse Agaricus bisporus with Agaricus xanthodermus, an inedible mushroom found worldwide in grassy areas, which smells of phenol and turns yellow when bruised, and which causes nausea and vomiting in some people.

This guide gives no foraging advice, and none should be taken from it. The safe way to eat button mushrooms is to buy cultivated mushrooms from a store or market. A wild mushroom that looks like a button mushroom is not a button mushroom until an expert has confirmed it, and appearance alone is never enough. The same caution applies to mushrooms that appear in a lawn or garden. They may be a related species, or they may be something else entirely, and the differences are often small. Mushrooms Growing in Lawn explains why fungi appear in grass and why the mushrooms in a yard should be left alone.

How Button Mushrooms Are Grown

Commercial button mushroom growing is a careful, controlled process, and it looks nothing like scattering seed in a field. Penn State Extension describes six main steps, from the start of composting to the final steam off after harvest, taking about 14 weeks to complete. The steps are Phase I and Phase II composting, spawning, casing, pinning, and cropping.

It starts with compost. Mushrooms extract the proteins and carbohydrates they need from a rich medium of decaying organic matter, and growers prepare that matter into nutrient dense compost. Phase I composting breaks down the raw ingredients, which are usually built around wheat straw and manure, until they become pliable and able to hold water. Phase II composting has two objectives: pasteurization, which removes undesirable insect pests, microbes, and pathogens, and conditioning, which creates specific food for the mushroom and a selective compost that favors its growth. During Phase II, the compost is held in the temperature range where microorganisms grow best, about 115 to 140 degrees Fahrenheit, and composting is considered complete when no trace of ammonia odor can be detected.

Spawning comes next. Mushroom spawn is a substance treated with mycelium, the network of thin, threadlike cells that forms the body of the fungus. The spawn production process begins by sterilizing a mixture of grain, water, and chalk, and then mycelium is added so active growth can begin. Spawn is typically made from a stored culture of millet, rye, or wheat, and it is used to seed the mushroom compost at the end of Phase II. Careful compost preparation reduces the chances of problems during the period from spawning through casing.

Casing means covering the spawned compost with a layer of material, usually peat based, that holds moisture and gives the mycelium a place to form mushrooms. Pinning follows. Mushroom pins develop once thick mushroom mycelia, called rhizomorphs, have formed in the casing, and fresh air must be introduced into the growing room, with carbon dioxide at 0.08 percent or lower depending on the cultivar, for the pins to develop properly.

Harvest begins 15 to 21 days after casing, which is 7 to 8 weeks after composting started. Mushrooms are picked over a period of 2 to 4 days in a 7 to 10 day cropping cycle, also known as a flush or break. Once the mature mushrooms are picked, the next flush moves toward maturity, and flush timing is managed through water, carbon dioxide, and temperature control. When a crop becomes unproductive it is terminated, and the spent mushroom substrate is pasteurized with steam before removal so that pests and pathogens do not contaminate neighboring or later crops.

The whole process runs indoors, in buildings equipped with ventilation systems, because the mushroom needs steady temperature, humidity, and fresh air at each stage. That is also why button mushrooms are available all year. The grower controls the season instead of waiting for one.

Cooking With Button Mushrooms

Button mushrooms are mild, and that mildness is their strength in the kitchen. Their flavor is gentle and earthy, with a soft savory note that deepens when they are cooked. Raw, they are firm and slightly crisp, with a clean, pale flesh. Cooked, they turn tender and take on the flavor of the butter, oil, garlic, herbs, or sauce they are cooked with, while giving back a light earthy note of their own. Because they are mild, they fit into dishes where a stronger mushroom would take over, and because they are firm, they hold their shape in soups, sauces, and sautes if they are not overcooked.

The simplest uses are often the best. Sliced raw button mushrooms add crunch and a mild earthy note to a green salad. Quartered or halved, they go into soups and stews, where they soften and absorb the broth. Sliced and sauteed in butter or oil with garlic, they make a side dish or a topping for steak, chicken, or toast. Whole small buttons can be roasted, and sliced buttons stir fry quickly with vegetables and noodles. Their mild flavor also makes them a good filler in pasta sauce, omelets, and pizza, where they add texture and body without changing the character of the dish.

A few practical points help. Button mushrooms are about 92 percent water, so they shrink as they cook and release liquid into the pan. A hot pan and a single layer give them a chance to brown instead of steam, and browning is what builds flavor. Salting at the start draws out water, so many cooks salt near the end. Mushrooms absorb water when they are soaked, so the usual advice is to wipe them clean with a damp cloth or a soft brush, or to rinse them briefly and pat them dry, rather than leaving them to soak. Trim the dry end of the stem if it looks rough, and use the whole mushroom, cap and stem, since the stem is edible and has the same mild flavor as the cap.

Storage is simple. Fresh button mushrooms keep best in the refrigerator, in their original box or in a paper bag, where air can move around them. A sealed plastic bag traps moisture and speeds spoilage. They are best used within a few days of purchase, while the caps are still closed, firm, and dry to the touch. A cap that has opened to show dark gills, a stem that feels slimy, or a mushroom with a sour smell has passed its best and should be discarded. Dried or frozen mushrooms are a different product, and this guide covers fresh button mushrooms only.

Cooking also matters for a simple reason. Button mushrooms are sold as a food to be cooked, and the recipes that use them are built around heat. Raw button mushrooms appear in salads, and that is a common use, but the mushroom’s flavor and texture develop most fully when it is sauteed, roasted, grilled, or simmered. A cook who wants the most from a button mushroom will give it a hot pan and a little time.

Nutrition

Button mushrooms are a low calorie food with a useful set of nutrients for their size. The figures below come from the United States Department of Agriculture FoodData Central entry for raw white mushrooms, FDC ID 169251, per 100 grams, which is about 3.5 ounces.

The pattern is clear. A button mushroom is mostly water, with a small amount of protein and carbohydrate, almost no fat, and very little sodium. Its strongest contribution is in the B vitamins, especially riboflavin, niacin, and pantothenic acid, where a 100 gram serving provides 20 percent or more of the Daily Value. It also provides 318 milligrams of potassium and 86 milligrams of phosphorus per 100 grams. That is a solid return from a food that provides only 22 calories per 100 grams.

Vitamin D deserves a separate note because the figure changes with light. Fresh button mushrooms contain only 0.2 micrograms of vitamin D per 100 grams, about 1 percent of the Daily Value. After exposure to ultraviolet light, the vitamin D2 content increases substantially, to 11.2 micrograms per 100 grams. That is why some mushrooms sold in stores are labeled as exposed to ultraviolet light or as a source of vitamin D. The vitamin D in an ordinary button mushroom is low, and the vitamin D in a UV exposed mushroom is much higher, and the label is the way to tell them apart.

None of this makes button mushrooms a medicine or a treatment, and this guide makes no health claims for them. The nutrition figures describe what the food contains, and that is all they do. A reader who eats button mushrooms as part of a varied diet gets a low calorie food with B vitamins and minerals, and that is the whole of the claim.

Button Mushrooms in the Wider Fungus World

A button mushroom is the fruiting body of a fungus, not the whole fungus. The larger, longer lived part of the organism is the mycelium, a network of fine threadlike hyphae that spreads through its food source. The mushroom is the temporary structure the mycelium raises to make and release spores. When the mushroom has finished, it decays, but the mycelium may remain and fruit again, which is why mushrooms can reappear in the same place in later seasons. The parts of that structure, cap, gills, stem, ring, and mycelium, are explained in Parts of a Mushroom.

In nature, Agaricus bisporus is a decomposer. It breaks down dead organic matter in rich soil and compost, and in doing so it returns nutrients to the soil. That role is easy to overlook when the mushroom arrives in a plastic box, but it is the reason the species could be farmed at all. The grower’s compost bed is a managed version of the rich soil and manure the fungus feeds on in a meadow, and the mushroom house is a managed version of the cool, damp conditions the fungus prefers.

The same habit explains why mushrooms appear in places where nobody planted them. A lawn, a garden bed, or a pile of compost can hold a mycelium that fruits after rain, and the mushrooms that appear are the visible part of a fungus already at work underground. Those lawn mushrooms are not button mushrooms, even when they look similar, and they should not be eaten on the strength of a resemblance. Mushrooms Growing in Lawn explains what those fungi are doing and why they are best left alone.

The button mushroom is also a reminder that a familiar food can have a long and surprising history. It began as a grassland fungus, it was first described as a crop by a French botanist in 1707, it was made reliable by pure culture spawn from the Pasteur Institute in 1893, and its white form came from a single chance mutation on a Pennsylvania farm in 1925. The mushroom in the produce box carries all of that history, and knowing it makes a plain ingredient a little less plain.

Frequently Asked Questions

Are button mushrooms the same as cremini and portobello mushrooms?

Yes. Button mushrooms, cremini mushrooms, and portobello mushrooms are all Agaricus bisporus, one species at different stages of maturity and in two color strains. The white strain picked young is a button mushroom, the brown strain picked young is a cremini, and the brown strain allowed to grow to full size is a portobello. They differ in size and in depth of flavor, not in species.

What is the scientific name of a button mushroom?

The scientific name is Agaricus bisporus. The genus is Agaricus, and the species name bisporus refers to the two spored basidia that produce its spores. The current name was given by Emil Imbach in 1946, after a taxonomic history that began with Mordecai Cubitt Cooke in 1871.

Where do button mushrooms grow?

In nature, Agaricus bisporus grows in grasslands in Eurasia and North America, in rich soil, compost, and manure. The mushrooms sold in stores are grown indoors by commercial growers, on composted substrate in buildings with controlled temperature, humidity, and fresh air, which is why they are available all year.

How can you tell a button mushroom from a similar wild mushroom?

A cultivated button mushroom has a smooth white to cream cap that is closed or only slightly open, a short stem with a narrow ring, and gills that run from pink in the young mushroom to dark brown as it matures. Several wild mushrooms look similar, and some are poisonous, including the death cap and the destroying angels, so appearance alone is never enough. This guide gives no foraging advice. Buy cultivated mushrooms from a store.

Are button mushrooms good for cooking?

Yes, within the limits of a mild ingredient. Button mushrooms have a gentle earthy flavor and a firm texture, they brown well in a hot pan, and they take on the flavor of the butter, oil, garlic, herbs, or sauce they are cooked with. They work raw in salads, sliced in soups and pasta sauces, sauteed as a side dish, and roasted or stir fried.

How many calories are in button mushrooms?

Raw white mushrooms provide 22 calories per 100 grams, according to the United States Department of Agriculture FoodData Central entry for raw white mushrooms, FDC ID 169251. A 100 gram serving also provides 3.09 grams of protein, 3.26 grams of carbohydrate, 1 gram of dietary fiber, and 0.34 grams of fat, with 318 milligrams of potassium.

How should button mushrooms be stored?

Keep fresh button mushrooms in the refrigerator, in their original box or in a paper bag that lets air move around them, and use them within a few days of purchase. Avoid a sealed plastic bag, which traps moisture and speeds spoilage. Use the mushrooms while the caps are still closed, firm, and dry to the touch.

Do button mushrooms contain vitamin D?

Fresh button mushrooms contain very little vitamin D, about 0.2 micrograms per 100 grams, which is 1 percent of the Daily Value. After exposure to ultraviolet light, the vitamin D2 content rises substantially, to 11.2 micrograms per 100 grams. Mushrooms sold as UV exposed or as a source of vitamin D carry that information on the label.