Have you ever taken a sip of wine and tasted green peppers, asparagus, or even cut green grass? These earthy and vegetative aromas are known as green notes and are a natural part of the bouquet of certain wines. But they can be undesirable to some wine drinkers, which is why a team from Australia has figured out a way to remove those flavour compounds while leaving the rest of the bouquet intact.
“Cabernet Sauvignon and Sauvignon Blanc, in particular, very much have these green characteristics. So it only becomes a potential issue when it’s out of balance with everything else,” said David Jeffery, associate professor in wine science at the University of Adelaide in Australia and lead author of the new research paper.
“Even a doubling of the concentration from 10 nanograms per litre to 20 is going to be enough to turn something that’s got a nice varietal characteristic … into something that just smells like green capsicum and sort of subdues the other fruity characteristics,” he said.
What goes into the taste of wine?
Green capsicum, also known as green pepper, is one of the stronger aromatic compounds. It takes very little to get a strong aroma and flavour coming off the wine. While it can be desirable in lower quantities, the wine starts to taste off with too much.
Wine taste and aroma result from thousands of chemicals that make up the bouquet and the chemicals can come from many different sources. Primarily, it`s the grapes themselves, but also the yeast produces a few essential flavour compounds, as do the oak barrels or the other treatment methods.
The green pepper flavour, specifically, seems to come almost exclusively from the grape itself. Often, picking the grapes a bit too early can result in a little more of a harsh flavour to the grapes and that comes through in the wine.
Removing the green taste
The researchers developed a nanopolymer—a tiny molecular framework, made mostly out of carbon—in a grey powder form that is designed to attach to the compound of the green capsicum flavour. The team also applied a magnetic field to the mixture to make the adsorption that much faster and more effective.
They also tested removing the flavour in both juice and mature wine and found that the best time to eliminate, or at least reduce the flavour compounds, is during the juice stage, as this is when they are most prominent.
Since most of the flavour profile of wines and food is in the smell, expert wine tasters participated in a smell test. The treated wines showed no reduction in the overall bouquet of aromas but seemed to have the capsicum notes reduced. The difference is subtle, but it looks like wines can be improved by filtration with this polymer to remove the green pepper taste, specifically.
The issue will be with regulations as the process of using the grey powder requires treatment with organic solvents and likely wouldn’t pass the very stringent rules for additives in wine or food. However, there remains a day where some of those off notes will be removed by passing the grape juice through a simple magnetized polymer filter. The result would mean more consistent and higher quality wines, even when starting from a less high-quality grape.