We all know aroma is vital at the start of a wine tasting experience, but it could be even more important at the end.
Research at the Australian Wine Research Institute (AWRI) suggests the long, lingering aftertaste that makes you want another sip of a good wine may in fact be due to retro-nasal perception of aromas released from molecules called glycosides, which occur naturally in grapes. We’ve always known they are there, but until now have not fully understood their potential.
‘People have considered the glycosides as a pool of latent flavour or potential flavour locked away in the grapes – sort of a nest egg to be released during winemaking or as the wine ages,’ said AWRI Senior Scientist Mango Parker, who is leading the four-year project that is funded by Wine Australia.
‘What we wanted to find out was whether glycosidically-bound aroma compounds in natural concentrations in wine can be unlocked while drinking and actually play a role in development of flavour after sipping some wine.’
The answer is that they are indeed active during wine consumption, but it was a complicated process to get to that answer – and not just for the researchers.
They had to extract glycosides, purify them to remove the bitter phenolics and free volatiles that might distract or confuse the testing process, then run a series of complex replicated blind trials over several days with a number of subjects and a number of wines with artificially set levels of glycosides. The tasters had to be trained to accurately assess and rate overall fruit intensity over a period of up to two minutes.
‘What happens with glycosides is that for many people initially there’s no flavour, then after maybe 10 seconds people start to notice it,’ Ms Parker said. ‘It reaches a maximum at about 30 seconds and then it declines. What we’re interested in is the maximum intensity, the overall amount of flavour and also the duration of the flavour.’
What particularly interested them was the great variation in the responses. They expected that some people would notice the impact of glycosides more than others, but were surprised at the difference in how people reacted to different types of glycosides. Some saw clear and strong lingering flavour from all of the glycoside compounds, while others perceived unlocked flavour from only certain types – and a quarter of people didn’t note any flavour at all.
‘This perhaps gives us some explanation about different preferences and different choices with wines; how people respond differently to different wines,’ Ms Parker said. ‘Some get a stronger lingering flavour while others don’t.’
The next steps (during the final year of this project and beyond) are to work out why the differences occur and what the options are to use this knowledge in the winemaking process.
Glycosides are naturally grape derived so there may be opportunities to use them. In a vintage trial this year, some glycosides were extracted from grapes and added to ferments to investigate their effect.
‘There are various ways it might be possible to modulate the glycosides in wine, including looking at increasing their concentrations in the grape during ripening and changing how they are extracted during winemaking,’ Ms Parker said.
‘Winemakers may want to consider whether to release locked up flavour earlier and produce a wine that has more upfront, quickly noticed flavour – or change winemaking techniques, such as avoiding certain enzyme preparations, and try to preserve that pool of precursors to give more lingering flavour in the finished wine.’
There are also exciting crossovers with research in other fields. Glycosides are in many different fruits and food products, and the release of flavour from glycosides may play an important part in everyday consumption of many foods. The process of retro-nasal aroma perception is also linked to the concept of satiety or ‘sense of fullness’ which, in turn, is linked to hunger and obesity.