The Only Way To Prevent Mushrooms From Turning Slimy

Mushroom experts weigh in.

Mushrooms in black container

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Mushrooms are delicate vegetables both in taste and temperament. If you forget to cook them right away, the mushrooms can go from beautiful to a sludgy, slimy mess in what feels like overnight. The key to longer-lasting fresh mushrooms is in how you store them after you bring them home from the grocery store. Proper storage and handling are what prevent mushrooms from going bad before you have a chance to eat them.

Preparing the mushrooms.
Simply Recipes / Alison Bickel.

What Causes Fresh Mushrooms To Go Bad

According to a study published by the National Library of Medicine (NLM), fresh mushrooms are very perishable—they rapidly degrade soon after being harvested. They lose their moisture, the color and texture change, and their nutritional value and flavor go down within a week.

Mushrooms have a high water content, about 90 percent, according to Harold McGee in On Food and Cooking: The Science and Lore of the Kitchen. That's why it's so hard to keep mushrooms fresh for long. They need to be stored in an environment with perfect moisture balance to prevent water loss and at the same time avoid condensation.

Also, mushrooms may continue to grow even after they've been harvested, and as McGee notes, "During four days’ storage at room temperature, they lose about half of their energy reserves to the formation of cell-wall chitin," the molecular name for mushroom fibers.

This is why you want to keep mushrooms in the fridge and not at room temperature. The NLM study says you can keep just-picked mushrooms at room temperature for one to three days, or up to seven days in the refrigerator. By the time you buy your mushrooms at the grocery store, they've been harvested for a few days, so it's best to place them in the fridge right away.

store mushrooms in a paper bag

Simply Recipes / Alison Bickel

The Best Way To Store Mushrooms

The first step in keeping mushrooms fresh for as long as possible is to make sure you're picking healthy-looking mushrooms. Look for mushrooms that look damp, but not wet or slimy. If you're buying them in bulk or at the farmers market, touch the mushrooms to check that they are not wet; otherwise, you're fighting a losing battle against the slime.

The number one rule when it comes to keeping mushrooms fresh is to let them breathe. Storing them in an air-tight container or in a plastic bag will cause condensation and speed spoilage. McGee writes that mushrooms, "should be loosely wrapped in moisture-absorbing packaging to avoid having the moisture they exhale wet their surfaces and encourage spoilage."

Also, adding excess moisture, either by washing your mushrooms before you put them away or wrapping them in a damp paper towel, does your fungi no favors.

You can use the original packaging—the paper cartons with perforated plastic wrap—from the grocery store because they are generally designed to allow airflow. You can also place mushrooms in a paper bag; just be sure to leave the top open. Pop the mushrooms in your fridge, unwashed, and be sure to use them soon! Uncooked mushrooms don't freeze well, so if you don't use them before they turn, you'll never have a chance at all. You're better off tossing (composting!) them.

A version of this article originally appeared on MyRecipes.com.