A pair of University of British Columbia scientists have identified chemical compounds previously unknown in wine and in grape seeds of the kind that give red wine its distinctive flavour profile and aging characteristics.
The researchers say their breakthrough could be a big step forward for winemakers who rely on extensive tasting alone to monitor balance and structure in fermenting and aging wines, but who do so virtually blind to the levels of important chemical flavour compounds.
The 14 phenolic compounds isolated and described by post-doctoral researcher Adeline Delcambre and chemistry professor Cedric Saucier at UBC’s Okanagan campus help form complex chemical compounds called tannins.
Winemakers control and develop the tannin content of red wines to create subtle flavours, dryness, astringency and rich colour. Tannins also affect how a wine changes during the aging process, affecting the flavour and hence the value of the wine, said Saucier.
Saucier hopes the discovery will lead to the creation of new tools that will help winemakers to measure the tannin content of grapes, their skins and seeds in the vineyard to determine when the fruit should be harvested and to monitor the development of tannins in wine as the freshly crushed grape juice “steeps” in its skins and seeds.
Phenols are particularly abundant in the skins and seeds of red wine grapes such as Cabernet Sauvignon, Syrah and Merlot
“That’s why you can make pretty good white wine from grape juice alone, but for red wine you really must have the whole grape,” said Saucier. “When you make red wine you macerate everything, the grape, the skins and seeds, and make an infusion.”
Winemakers must rely mainly on their sense of taste to determine when a grape is ready to be picked and to decide on the moment when the tannin content of grape juice stewing with its skins and seeds — a slurry called the must —is just right and it needs to be strained.
“You want to extract some of these compounds, perhaps half of them, but not all of them,” he explained.
Winemakers try to taste for the balance of phenols in grapes and in the wine, which is based more on art and experience than science
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