Portobello Mushrooms (Agaricus bisporus)

Portobello mushrooms are just large cremini mushrooms, and their size makes them perfect for grilling or roasting. Portobello is usually the preferred name but whether the name Portobello is substituted with cremini, OR matsutake, OR porcini, they all refer to the same thing: a brown, large version of your basic white button mushroom.

The mushroom is also called a brown cremini mushroom or a table mushroom. In Northern Italy, the mushroom is called cappellone.

Identification tips and Habitat

The cap of the original wild species is a pale grey-brown in color, with broad, flat scales on a paler background and fading toward the margins.

It is first hemispherical in shape before flattening out with maturity. The narrow, crowded gills are free and initially pink, then red-brown and finally a dark brown with a whitish edge.

The cylindrical stripe is wide and bears a thick and narrow ring, which may be streaked on the upper side. The firm flesh is white though stains a pale pinkish-red on bruising.

Commonly found in fields and grassy areas after rain from late spring through to autumn worldwide, especially in association with manure. It is widely collected and eaten, even by those who would not normally experiment with mushrooming

Portobello Mushroom Nutrition

raw 100 grams
• Calories 26
• Total fat (g) 0.020
• Saturated fat (g) 0
• Monounsaturated fat (g) 0
• Polyunsaturated fat (g) 0
• Dietary fiber (g) 1.5
• Protein (g) 2.5
• Carbohydrate (g) 5.07
• Cholesterol (mg) 0
• Sodium (mg) 6

Cultivating Portobello Mushrooms

Mushrooms being fungi do not grow like a regular garden vegetable. They are  generated from spores, not seeds. They contain no chlorophyll.

When growing, their nutrients are delivered from the medium they are grown in and absorbed through the root system supporting the mushroom, which is called the mycelium. The mushroom cap and stem that we see in grocery stores is actually the fruit of the mycelium.

In commercial mushroom farming, the entire process of collecting spores and growing spawn is done in a sterile lab. As such, growing mushrooms from scratch may not be the best option for either the casual gardener or the hardcore green thumb.

If you are interested in growing your own mushrooms, you can simply order kits that contain pre-inoculated media or that require you to do the inoculation yourself. There are many sources available online — Mushroom Garden 

The kits range from the low end box of mycelium and medium for indoor growing, to much higher end (and more complicated) “systems” that enable you to inoculate your own substrate.

After receiving your kit, you must maintain a proper temperature and moisture level throughout the incubation period that is required for the mycelium to colonize the substrate. This process usually takes a week to ten days.

The next step is to force the fruiting of the mycelium by keeping the kit moist and, in the case of Portobello mushrooms; the requirement for darkness, often thought to be common to all mushrooms, is actually unique to Portobello mushrooms and their relatives the White and Cremini mushroom.

Other varieties, like Shiitake and Oyster mushrooms, require some light. Most kits have a tent to retain moisture, but you do need to spray regularly. And you need to use the right kind of water – chlorine is a no-no, so if you must use tap water, you need to let it sit overnight so the chlorine can evaporate.

Most kits produce mushrooms within a couple of weeks. Each harvest is called a flush and you can expect about two or three flushes per kit. Portobello kits yield about 3-6 pounds of mushrooms over three months.

My advice

• Purchase a mushroom growing kit to keep it simple, since inoculating your own growing medium with Portobello mushroom spores is complicated, more expensive, and more prone to failure.
• Set up your kit and be sure to follow instructions for the temperature and humidity you must maintain in your growing area during the “colonization” period, which is usually about 10 days. Typically, mushrooms require a temperature between 60 and 80 degrees Fahrenheit in order for the mycelia to grow.
• Force fruiting of the mycelium by keeping the medium moist and the growing area totally dark. If you order a kit that includes a tent, this can help to retain the moisture this mushroom needs. Also spray daily with water that contains no chlorine.

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