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The Lowly White Button Mushroom

Gary Gilbert

By Gary Gilbert 



The common White Button Mushroom is probably the most famous fungal fruiting body. It is found in virtually every grocery store in the world. It is an essential culinary delight, though substantially flavorless, when eaten raw or cooked, as compared to its wild cousin, Agaricus campestris. It goes by a huge variety of common names. However, its accurate species name is Agaricus bisporus, with common names including Pink Bottom, Meadow Mushroom, Swiss or Roman Brown Mushroom, Hot-Bed Mushroom, Field Mushroom, or the French “Champignon de Paris.” 


So, what is the difference between the Cremini, Baby Bella, and Portobello mushrooms we see in the stores? Well, they are all simply “varieties” of the exact same species of fungi. That means they have different macroscopic features or simply ages of growth but still contain the same DNA. As they say in Thailand, “Same, same, but different!”


Crimini and Baby Bella are the same species but slightly different strains than the Portobello. They are harvested when the cap is still closed or slightly opened, which keeps their flavor a little less intense. This is good for me because their flavor can hit you like a steamroller. Their gills have started to mature and produce spores, so they will be less pink and start to get that nice chocolate brown color that Portobello’s have. Their flavor is stronger than the white Button Mushroom but not as strong as their heavy-hitting cousin, the Portobello. Portobellos are large, fully mature Agaricus bisporus. Their gills are dark chocolate brown, and their flavor is nutty and almost meaty, so they work very well as a meat substitute in, for example, a vegetarian hamburger. Because of their large size they are also quite versatile and can be stuffed or grilled and fill up a dinner plate quickly.


If anyone thinks that mushrooms are inconsequential in terms of nutrition, think again. Button mushrooms provide protein and vitamins B, C & D, iron, magnesium, phosphorus, potassium, sodium and zinc. That’s more than most vegetables will give you.


White Button Mushrooms are grown in dark warehouses, caves, and tunnels. Historically, they were grown in the catacombs of Paris. These decayers or saprotrophic fungi need nutrient-rich soil or substrate to grow in. Actually, they are second-stage decomposers, meaning that they do not decay the substrate directly like Shiitake or Oyster mushrooms but require a substrate that other organisms have first broken down. 


Growing Button Mushrooms is a 6-stage process: 


First, farmers make long rows of organic material about six feet high and let bacteria digest it for a week or two. These piles heat up like your backyard composting bin would do. They are turned and aerated while the heat generated pasteurizes the soil and kills anything that could contaminate the spawn. 


Next, they move the substrate to trays to allow it to cool a bit further and flush out any ammonia vapors. All of the ammonia has to be eliminated in the end, or it will kill the Agaricus mycelia once it is introduced into the substrate. 


Third, the substrate cools further, and the mushrooms are introduced, having been started at a separate facility on sterile grain. Growers can get all sorts of subtle variations of Agaricus strains that produce white, off-white, cream, or brown-capped fruiting bodies. The heat and humidity are controlled to keep things moist and warm but not hot, as are the carbon dioxide levels. A week and a half to three weeks will pass as the mycelia grow throughout the substrate.


Fourth, an inch or two of top soil is added, locking in the soil moisture and starting the growth of the fruiting bodies called ‘pinning’. This takes only a few days to occur, and high humidity and very little light are the keys to this stage.


Fifth, the temperature and carbon dioxide levels are decreased, and the mushrooms begin to grow. This takes about two to three more weeks.


Finally, the huge, dense flushes of fruiting bodies grow to maturity in cycles of about three to five days each. The substrate is exhausted after about three to five flushes of fruiting bodies have been produced, and it can be recycled once again or used as garden compost. Most Button mushrooms are picked while their caps are still closed and attached to the stem, hence the term ‘Button Mushroom.’ The complete process can take about three and a half months.


Gary Gilbert is on the Executive Committee of the Boston Mycological Club, has recipes in the Fantastic Fungi Cookbook, and is the author of Mycocards, a flashcard for learning mushrooms by genus, www.mycocards.com.


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