what is milky substance when onion is cut?
While growing, onions pick up sulfur from the soil which gives them their pungent and eye-burning character. When cut, onions release a milky substance containing sulfuric acid, sulfur dioxide, and hydrogen sulfide (the latter which causes teary eyes). A sweet onion, such as the Vidalia, is grown in soil with less sulfur. When serving onions raw it is a good idea to rinse or even soak them briefly. Cutting onions can ruin painstakingly-applied mascara so it is best to tend to them before donning makeup. The sulfur will dissipate quickly.