Despite the extensive information published on flavour chemistry, odour thresholds and aroma descriptions, the flavour of complex products such as wine and brandy cannot be predicted. With a few exceptions (e.g. terpenes in the aromatic varieties and alkoxypyrazines in the vegetative or herbaceous cultivars), perceived flavour is the result of specific ratios of many compounds rather than being attributable to a single “impact” compound [21,107]. In wines and brandies, the major products of yeast fermentation, esters and alcohols (Figure 22), contribute to a generic background flavour, whereas subtle combinations of trace components derived from the grapes usually elicit the characteristic aroma notes of these complex beverages.