Litmus "Lecanora tartarea" (Norway, Sweden), "Variolaria dealbata", "Ochrolechia parella", "Parmotrema tinctorum", and "Parmelia". Currently, the main sources are "Roccella montagnei" (Mozambique) and "Dendrographa leucophoea" (California). The main use of litmus is to test whether a solution is acidic or basic. Wet litmus paper can also be used to test for water-soluble gases that affect acidity or alkalinity; the gas dissolves in the water and the resulting solution colors the litmus paper. For instance, ammonia gas, which is alkaline, turn the red litmus paper blue. Blue litmus paper turns red under acidic conditions and red litmus paper turns blue under basic or
Olive oil acidity attacked by flies and parasites), bruised olives, delayed harvesting and storage before processing. The lipolysis reaction is greatly enhanced by the presence of an aqueous phase, so when oil is separated from water during processing, lipolysis slows down and stops. Free acidity is a defect of olive oil that is tasteless and odorless, thus can not be detected by sensory analysis. Since vegetable oils are not aqueous fluids, a pH-meter can not be used for this measure. Various approaches exist that can measure oil acidity with good accuracy. The official technique to measure free acidity in olive oil (as defined