Wine flavour precursors revealed in new research

It’s the sort of research – and topic – that can’t help but pique the interest of wine drinkers and scientists – what really causes the flavours and lingering aftertaste we get in our mouth when we taste a memorable glass of wine.

For the past 14 months, scientists at The Australian Wine Research Institute (AWRI) have been looking in depth at glycosides – flavour compounds attached to sugars in wine – and have shown they play a role in the development of the in-mouth flavour we perceive when drinking wine.

Now, with proof of concept achieved, the AWRI team is moving onto even more exciting discoveries.

The four-year project is funded by the Australian Grape and Wine Authority and titled, ‘Flavour precursors: contribution to wine aroma, in-mouth sensory properties and flavour release’.

AWRI scientist Mango Parker said the first year of research had delivered some mixed results.

“First, we extracted flavour precursors, targeting glycosides in particular, from a range of Chardonnay and Shiraz wines and tasted them in a blind tasting,” Ms Parker said.

“Unfortunately there was almost no detectable flavour that developed in the mouth arising from the glycosides. Luckily we had included a wild card Gewurztraminer wine that was loaded with monoterpene glycosides, and tasters could detect a floral or fruity flavour that built in the mouth after tasting.

“I should point out that we went to great lengths to make sure that we removed all the volatile aroma compounds, so our precursors didn’t have any noticeable floral or fruity smell.”

By removing the aroma-causing compounds from the wine, Ms Parker said they could be sure that any flavours that developed in the mouth immediately after tasting were due to glycoside precursors releasing aroma compounds by a process called hydrolysis.

“When we started in this area just over a year ago, we didn’t know for sure if the flavour precursors naturally present in grapes and/or wine would be potent enough to be able to taste in a wine-like matrix,” she said.

“We’ve since followed up with a formal sensory study with randomised order, triplicates of each sample and even black glasses to conceal any slight colour, which confirmed our findings.”

Prior to starting this research, Ms Parker was investigating the role of glycosides in relation to smoke taint.

“The chemistry going on in this current project, the hydrolysis of glycosides in the mouth, is similar to what was seen with smoke taint,” Ms Parker said.

“In that case, we could explain why some wines could smell fine (no unusual smoke aroma) but after wines were tasted, volatile phenol glycosides could impart a smoky, ashy flavour that some people found objectionable.

“We investigated things like the effect of alcohol and pH on this phenomenon, and did a series of thorough sensory experiments including a full reconstitution study. So we knew that glycosides could impart lingering flavours to wine, if the compound attached to the sugar was potent enough and the concentration of the glycosides was high enough.”

In the case of smoke taint the glycosides were present due to a contamination of the grapes by smoke, but Ms Parker said her current project was focusing on naturally occurring flavour precursors and, thankfully, “more of the pleasant flavour spectrum”.

Eventually, she said, the final goal of the project will be to develop a better understanding of the flavour of wine in-mouth that is due to precursor compounds, as well as retronasal (aroma by mouth) perception of volatiles.

“For the wine scientists, it will mean being able to characterise glycoconjugates and amino acid conjugates of volatile compounds,” Ms Parker said.

“We will be able to assess the extent and sensory significance of in-mouth breakdown of glycosides, amino acid conjugates and free volatiles such as esters and determine the relationship between levels of key precursors in grapes and the amounts remaining in wines.

“We should also be able to determine the effect of other wine constituents, such as alcohol and non-volatiles on in-mouth release and sensory properties of precursor-derived volatiles.

“Winemakers will have a better understanding of the factors that are important for flavour persistence and overall intensity, which are important features of high quality wines.

“This will lead to better analytical targets for quality markers for grapes and wines,” Ms Parker said.

 

Scientists at The Australian Wine Research Institute (AWRI) are investigating the development of the in-mouth flavour we perceive when drinking wine.
Scientists at The Australian Wine Research Institute (AWRI) are investigating the development of the in-mouth flavour we perceive when drinking wine.