Do amino acids play a role in the flavour of red wine?
Indeed they do, with new research showing they have a surprisingly strong influence on the sensory properties of red wine – building sweetness and viscosity, and increasing the flavour intensity associated with full-bodied wines.
Grape amino acid concentrations are often measured in relation to fermentation performance and as precursors to some wine volatile compounds. However, the most abundant residual amino acid in wine, L-proline, is often not considered as it is not metabolised by yeast under winemaking conditions.
“We wanted to know whether L-proline – along with another key amino acid that tastes savoury, L-glutamic acid, played a role in wine flavour – either directly, or indirectly,” said principal investigator, Damian Espinase Nandorfy from the Australian Wine Research Institute’s Sensory and Flavour Research Group.
To determine this, Damian and the research team conducted a series of sensory-guided experiments where they added amino acids L-proline and L-glutamic acid, along with tannins and volatile compounds, to red wines.
“In an initial study in model wine, low levels of amino acids were found to interact with volatiles to modulate bitterness. Exploring this interaction further, L-proline and L-glutamic acid were added to a Shiraz wine containing naturally low levels of these compounds,” Damian said.
L-proline was found to increase sweetness, viscosity and red fruit flavour, and decrease bitterness and astringency. Furthermore, L-glutamic acid imparted savoury/umami taste to the wine.
A final experiment reconstructing the Shiraz wine, with or without added L-proline, confirmed that it enhanced fruit flavours.
“Overall, these amino acids may be part of the story behind desirable ‘fruit sweetness’, ‘savoury’, ‘fullness’ and the perception of ‘soft tannins’ in dry reds,” Damian explained.
Damian said the research findings were important for winemakers and growers.
“This foundational work elevates amino acids as a new class of taste-active compounds, with L-proline identified as a natural, non-carbohydrate sweetener which adds viscosity and has a positive influence on red wine flavour and mouthfeel.”
He said natural L-proline levels could be increased by producers through known viticultural techniques and also had potential to improve no and low-alcohol products as an additive.
In line with this, Affinity Labs, the commercial arm of AWRI, will be offering rapid analytical testing for proline concentration in red and white wines.
Damian said some of the findings in the project were very surprising, “because we assumed that over the past six decades of wine research the possibility of a direct taste effect of residual proline would have been already tested in wine, as high amino acid concentrations have been extensively reported in viticultural studies – but it wasn’t.” In fact, the team found only two studies – and neither had been followed up with sensory studies.
The team’s experiments demonstrating the amino acid influence have now been continued in another study blending commercial red wines naturally low, medium and high in proline, tannin and flavour compounds to understand the practical application of this fundamental work.
“Again, the results show very similar enhancement of ‘sweetness’, ‘viscosity’ and ‘fruit flavour’ in commercial proline-rich blends which were also the most liked by consumers compared to the low proline wines,” Damian said.
The details of this practical study, which gave proline wine blends to over 120 regular red wine consumers, will be available in a publication coming out later in the year.
Damian presented his findings at a Fresh Science session at AWITC recently and was awarded Best Oenology Presentation at the conference.
Damian Espinase Nandorfy from the Australian Wine Research Institute’s Sensory and Flavour Research Group