grape quality assessment is needed by winemakers for long-term strategic planning and, in the short term, for the planning of each vintage, especially in fixing harvest dates. Assessment is often a matter of combined judgement by grape-growers and winemakers, using experience of the performance of previous vintages as the main guide, supplemented by tasting of berries and by measurements of grape composition (see sampling and analysis). In some regions, sugar content (see must weight) is sufficient to indicate forthcoming wine quality, especially in cool regions (unless, of course, major catastrophes such as disease intervene). In warm to hot regions, sugar alone is an unreliable guide to quality and additional measurements are needed: total acidity and ph of the juice are useful, as well as some measure of the colour of skins in some red grapes. The importance of aroma is increasingly recognized, but it is difficult to measure. Valuable information can be obtained by collecting and storing juice samples at intervals during grape development and running comparative ‘sniffing tests’, but these are costly and difficult because of their subjective nature. An experimental technique, glycosyl-glucose assay, was developed in the mid 1990s to supplement these methods. This gives a measure of the total glycoside concentration in grapes, which include flavour precursors of some varietal flavour compounds. A more recent development in grape quality assessment is the use of near infrared spectroscopy to measure rapidly many different grape constituents, including red grape colour, expressed as the concentration of total anthocyanins.
