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 flavour precursors in winemaking
To better understand the types of flavour precursors present in grape skin, and their role in wine flavour, numerous marc samples from different varieties were extracted and analysed. Non-targeted liquid chromatography tandem mass spectrometry analysis provided by Metabolomics Australia gave several hundred structural molecular features of interest that can be used to define the glycoside extracts. Interestingly, there was little difference between the profiles of white and red varieties. A Muscat à Petit Grains Blanc extract was found to be unique due to the presence of specific glycosides of phenylethanol, a compound with a ‘rose-like’ aroma. Glycoside material isolated from the grape marc of a dozen varieties was added back to a base Chardonnay wine. After five months of storage, the extent of breakdown and subsequent release of aroma was assessed by a rapid sensory method, with results indicating that the source of the grape marc glycosides heavily determined the aroma outcome.
Moving outcomes towards impact
The increased flavour from marc-derived glycosides observed in this project formed the basis of a joint AWRI/Wine Australia team in the 2019 CSIRO ON Prime program. Team ‘Wine-grape extracts’ used the ten-week program to explore the potential for natural flavours extracted from wine-grapes to be used in wine products and other beverages and foods. The team members conducted more than 100 conversations across different industry segments, participated in coaching sessions and learned from a team of program mentors. The team was awarded the facilitator prize for its commitment to the ON Prime strategy of customer-led discovery, ensuring the right questions were being asked through market validations within different segments, and building business model capabilities.
Josh Hixson, Mango Parker