Luffa refers to the vine part of Luffa plant, which can be used to boil water or make soup. The substance released by towel gourd contains a bitter ingredient, so sometimes the boiled water has some bitterness. Not all loofah will produce bitterness, because the degree of bitterness is related to the varieties, storage time and treatment methods of loofah. In order to reduce the bitterness, you can soak the towel gourd in salt water before boiling, or boil it, pour off the water and cook it again.