Using glycosides and other flavour precursors for improved wine flavour
It has recently been demonstrated that purified non-volatile glycosides present a valuable, novel opportunity to increase flavour in wine. They can contribute flavour through enzymatic release of volatile aroma compounds during fermentation and winemaking, and by in-mouth breakdown during wine consumption, boosting flavour intensity and aftertaste.
This project will assess the effect of enhancement of grape glycosides in juices and wines. Characterisation of glycoside extracts from various grape varieties will be achieved using LC-MS and GC-MS analysis. Glycosides from different varieties will be extracted and partially purified, their stability investigated during fermentation and wine ageing, and their sensory impact investigated.
The concentration of residual precursors in wines following fermentation will also be measured, to determine whether these may act as quality markers. Additional flavour release systems such as thiol precursors will also be assessed, providing a complementary avenue for building additional flavour. A better understanding of the factors underlying individual variability in sensory response to in-mouth release of aroma from precursors will also be obtained.
Understanding glycoside flavour precursors
Storage trials of grape marc-derived extracts rich in monoterpene glyco¬sides showed a strong dependence of the observed flavour evolution on the original source of the extracts. For example, grape marc from Muscat varieties yielded extracts that were highly potent and led to the evolution of significant quantities of ‘floral’ monoterpenes in Chardonnay wines after six months of storage. As such, accessing grape marc from aggregated sources of numerous varieties (e.g. from processing facilities) may not be ideal for the potency of the resulting extracts.
The rate of release of monoterpenes from glycosides was also characterised, partly to assist in future accelerated ageing studies to better predict outcomes following bottle storage. First-order rate curves provided a means to determine reaction half-lives for the breakdown of geraniol glucoside, and were related to the monoterpene composition in wines.
In-mouth release of ‘tropical fruit’ thiols
Sauvignon Blanc juices with known concentrations of amino acid-bound thiol precursors were extracted to yield a thiol precursor-rich extract. The extract was added to water and model wine and subjected to sensory evaluation for in-mouth release potential. Initial results did not look promising in establishing an in-mouth flavour contribution for thiol precursors, with only weak flavour evident in the water solutions approximately 30 seconds after tasting.
Josh Hixson, Mango Parker