A colour index for the objective determination of the colour in red table grapes
is described. This index is based on the CIELAB values. A statistical study
revealed a high correlation between L* and b*, while a* was not a representative
parameter. The usefulness of this index is investigated to classify the red
grapes depending on their external colour. The proposed colour index for red
grapes (CIRG) is based on the parameters L* (lightness), H (hue angle) and C
(chroma) and its expression is “(18O_H)l(L* + C)“. All the colour indexes previously
proposed were defined in fruits whose colour varied between yellow and
red, and, therefore, were not suitable for red grapes which show a dark violet
colour. This new index showed a good linearity with the visual colour of the
berries and distinguished between sample groups of different external colour.