Beware of the mushrooms (fresh or dried) sold in Hong Kong, their sources are mainly from China or Hong Kong. I remember having heard that these mushrooms are grown out of waste cotton many years ago. I confirmed this with my husband and he said yes, they're either grown out of waste cotton or wood dust. If you buy them from the local fresh food market (any kind of fresh mushrooms) they all smell and taste sour. Those that are sold in Wellcome don't smell sour. I don't know if it's because their source is different from the local market or they are refrigerated so they don't smell sour. Whenever I buy something that smells sour, I rinse it in boiling water.
Mushrooms that are grown naturally or wild mushrooms are almost extinct, those grown by using wood will state in their packages and are definitely more expensive. However, I still buy mushrooms because my daughter and I love them.