White button mushrooms for a What to Eat HEALTH article.  (Photo by Ricardo DeAratanha/Los Angeles Times via Getty Images)
Food - Drink
Why You Should Think Twice Before Throwing Out Old Button Mushrooms
By JOHN J LEE
White button mushrooms are the most popular mushroom in the United States, making up a whopping 90% of all mushrooms consumed. However, buying large amounts of these mushrooms means a higher risk of spoilage, so if you suspect your mushrooms are too old, examine their texture and smell.
If the surface of your mushrooms is slimy, overly wrinkled, and has very dark spots, or if the mushrooms emit a sharp and foul-smelling odor, it means they have gone bad. Still, you shouldn't just toss your mushrooms without examining them, because aged mushrooms can still be perfectly fine to eat.
In a side-to-side taste test of differently aged mushrooms, conducted by Cook's Illustrated, some older mushrooms that had slight blemishes and wrinkling also had more depth of flavor. While you still must carefully examine your food, mushrooms that have dried up a bit can still be a tasty addition to pasta or served over meat.