The grill is the perfect piece of equipment for cooking mushrooms. Because mushrooms contain a high percentage of water they can remain moist under high, direct heat. As mushrooms lose moisture, the flavor of the mushroom (and anything you have added to them) is intensified.
The trick with mushrooms is knowing the best cooking method for the mushroom size and how to add flavor as you grill them.
You can grill mushrooms of any size, but you will need to use different equipment and cooking methods based on the size of the mushroom you are cooking.
For example, large portabello mushrooms, which are perfect as a substitute hamburger patty, can be grilled as is, right on the grate. Any types of mushrooms that are large enough to not to slip through the cooking grate can be cooked directly on the grate.
Mushrooms can lose as much as 50 percent of their size as they cook. Smaller mushrooms can be threaded onto skewers for easy control on the grill. Be gentle with mushrooms as they can break easily. It might be best to use tongs for turning and not forks or spatulas.
Many people say that you should not wash your mushrooms in water. Many cookbooks suggest that mushrooms should only be gently brushed off to clean off any remaining dirt or debris. The truth of the matter is that most restaurants, even the fancy ones, rinse off their mushrooms to get them clean. You can do individually brushing if you have a lot of free time, but water will not harm mushrooms if you rinse off the mushrooms right before cooking.
As for the stems, trim off the dry end, unless the stem is going to get in your way like for a portabello mushroom burger. If you are using mushrooms as kebabs, leave the stems intact. Stems are denser and will help the mushroom hang on to the skewer.
Flavoring Your Mushrooms
You have several options when it comes to flavoring your mushrooms, you can marinate them, mop them with a sauce, or sprinkle seasoning on them while on the grill.
Mushrooms can dry out if you do not replace the moisture that cooks off on the grill. An oil-based marinade will help lock in moisture. Basting while grilling will keep your mushrooms moist.
You can marinate mushrooms well in advance—up to a day or so. Mushrooms are very forgiving that way and since they are going to be clean of bacteria you do not have to worry about the marinade becoming contaminated.
If you choose not to marinate the mushrooms, the mushrooms can be seasoned right on the grill. Mix a small amount of olive oil, garlic, salt, and other seasonings and baste (or mop) this onto the mushrooms as you cook them.
If you are preparing mushrooms as a side dish, season them with the same spices that you use for the main dish. This provides complimentary flavors that tie the meal together.