Grape berries are commonly perceived to be composed principally of high concentrations of
fermentable sugars, accompanied by a complex suite of polyphenolic compounds responsible for colour and
‘mouthfeel’ properties. The organic acid composition of the berry, which is principally a reflection of the
metabolism of tartaric and malic acids during development and ripening, has several important consequences for
the use of grapes in winemaking. Early research showed two unusual features of acid metabolism in grapes – the
occurrence of significant concentrations of tartaric acid, and a marked decrease in the concentration of malic
acid as berries enter the ripening stage. Despite a few ‘false starts’, a synthetic pathway that led to the formation
of tartaric acid from ascorbic acid was identified, and in the past few years it has been proved possible to
confirm this by biochemical and molecular biological approaches. Evidence for the synthetic route to malate
formation in the berry proved simpler to identify, but the greater metabolic versatility of malate compared with
tartaric acid, and the post-veraison breakdown of malate by a variety of pathways have ensured a continuing
interest in this component of the berry’s acid complement. Modern ‘post-genomic’ approaches have been
increasingly used to enable the measurement and analysis of berry metabolism. These approaches, and the
advent of a readily transformable ‘model’ grapevine system, will undoubtedly continue to play a major role in
the development of the understanding needed for the rational modification of berry acid composition in response
to changing environmental and cultural practices.
Keywords: Ascorbic acid, Malate dehydrogenase, Malate synthesis, Malic acid, Organic acid,
Oxaloacetate, PEP carboxylase, Tartaric acid, Tartrate synthesis.
