Andrade Peptone Water with Meat Extract (Revised as Andrade Peptone Water with HM Extract) is a basal medium for studying fermentation reactions, particularly of members of the Enterobacteriaceae. This medium is the most commonly used media for carbohydrate fermentation. Desired carbohydrate is added to the medium, which is inoculated with the test organism. If the test organism metabolizes the added carbohydrate, acids are produced thereby lowering the pH of the medium. This causes a subsequent color change of the indicator, from colorless to pink to red. If the added carbohydrate is not metabolized, the medium remains pale tan to straw colored. Gas produced during fermentation is collected in the Durhams tube.