Abstract: Analytical methods and devices according to the present disclosure may be used to assay the concentration of malic acid, or related species, in a sample, e.g., preparations of fruit, vegetables, juice, and/or wine. Liquid samples are combined with a reaction mixture, incubated, and a parameter characteristic of the resulting incubated mixture is measured. During the incubation, the reaction mixture generally reacts with the liquid sample to transform malic acid or related species that is present in the liquid sample. The measured parameter may be pressure, pH, an amount (e.g., volume, mass) of CO2 generated during the incubation, a parameter related to the foregoing, and/or any other parameter related to the amount of malic acid or related species transformed.