Monoterpene diols from grapes

The Monoterpenes. Monoterpenes are not major components of nonfloral grapes (1 ) although some of these compounds were present in each of the three varieties. In a previous survey of monoterpene diols in floral eind non-floral grapes, (Z)- and (E)-2,6-dimethylocta-2,7-diene-l,6-diols 11 and 12 were not found in the Chardonnay samples examined ( ). Observation of these diols in the Chardonnay here, and reports of their occurrence in several other Chardonnay clones (7), indicates that these compounds 11 and 12 are common monoterpenes of grapes. No products obviously derivable from a conjugate of diols 11 and 12 were seen in the acid hydrolysates, vAiich is consistent with the previously reported stability of the 1,6-diol system in these compounds ( ). 

The monoterpene pattern can be used to differentiate cultivars. For example, a clear distinction can be made between wines from the grape cultivar White Riesling and wines from other grape cultivars which are also sold as Riesling . As shown in Fig. 20.7, the monoter-pene concentrations (especially of linalool, hotrienol, a-terpineol, and 3,7-dimethylocta-l,5-fraws-dien-3,7-diol) in White Riesling are considerably higher than in the other Riesling wines. 

---