Is it safe to not wash mushrooms?

I have read a couple of experiments (in Dutch so I will not link them here) where people cooked the same dish from the same shrooms, with one batch brushed and the other washed.

The washed batch did need higher temparature to actually fry, instead of just boiling in their own moisture and the texture in the finished dish remained different. There does seem to to be some merit to the culinary traditions here.

As for the safety aspects, perhaps this will ease your mind somewhat:

Research minimizes effects of federal produce standards on mushroom industry:

But a new study shows that heat generated during the traditional composting process -- originally developed to kill insect and fungal pests of mushrooms -- is adequate for eliminating human pathogens that might be present, according to researchers in Penn State's College of Agricultural Sciences.

If you got sick from eating a dish, the cause may not have been in the nutrition beds the shrooms were grown on.

Alton Brown, Harold McGee, Robert Wolke, and Kenji Lopez Alt have all tested washing mushrooms by weighing them pre and post wash, and found they absorb an insignificant amount of water that does not significantly affect cooking time. Both McGee and Wolke tested by soaking the mushroom for five minutes rather than simply rinsing. They all encourage washing mushrooms. Several suggest washing them, using a salad spinner, and then cooking slightly longer. For example, Lopez Alt's testing found they absorbed only about 2% of their total weight which translated to an extra 15 to 30 seconds of cooking time.

McGee describes his process in The Curious Cook, Wolke in What Einstein Told His Cook, Lopez Alt in The Food Lab (and also Serious Eats) and the best I could find for Alton Brown were transcripts from the Good Eats Fan Page.

Wash right before using - not storage. Also, as Wolke notes, mushrooms are already mostly water to begin with - if your mushrooms are steaming rather than browning, it's more likely that your pan is too crowded, rather than a function of having washed them.

Honestly, I would wash them. I don't care if that affects the taste slightly. Eating unwashed fruits and vegetables (especially raw) is a risk factor for many diseases such as listeria, salmonella and toxoplasmosis. Don't soak the mushrooms to wash them, give them a quick rinse under warm water, and use your fingers to clean the dirt off them. Then pat dry with a towel, and let air dry, before adding them to your dish.

Most mushrooms are not grown in manure but rather in dirt under a layer of peat moss. Mushrooms consist mostly of water so rinsing them quickly and drying with paper towel will not change the flavor or browning time.

I thought everyone peeled mushroom caps with a pairing knife. That's how I was taught to clean them. It's a bit labor intensive, but usually the number of mushrooms used is not that large. Holding the stem with a paper towel usually cleans it, or simply cut the stem and do not use it.

I definitely agree with most chefs, that mushrooms should not be washed. They are kind of like sponges, so when you sautee them in butter, you want them to absorb the butter, and get crunchy. Also, all the mushrooms I've ever seen, only have a bit of peat moss on the bottoms of the stems; no dirt, and certainly no manure. I also agree with the fact that a little bit of bacteria is good for our immune systems, as well as the fact that most people are germaphobes nowadays. Also, most people are so stubborn and do not want to listen to any proof contrary to their beliefs, and therefore: if you're a germaphobe, rinse your mushrooms, or else you won't enjoy them, because you'll be obsessing about bacteria and want to vomit. Definitely not very appetizing, Imo.