Honey bees add an enzyme, called glucose oxidase, to the collected nectar during the honey-making process, which converts the glucose in the honey into hydrogen peroxide (H2O2) and gluconic acid. H2O2 is toxic to many microbes. During the ripening of honey, glucose oxidase is inactivated but regains its activity if the honey is diluted. In a study by Kwakman et al, it was found that Revamil honey produced 3.47 _ 0.25 mM H2O2 in 40% (v/v) honey after 24 hours, but no H2O2 was detectable in the Manuka honey they tested, suggesting that nonperoxide factors are responsible for the antimicrobial activity of Manuka honey.