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How wines get their complex flavors

(Styling by Sheryl Julian/Globe Staff; photo by Keith Bedford/Globe Staff)

Wine professionals are fascinated with what gives the drink its distinctive character. The ability to distinguish individual flavors and aromas, with precise detail, has become all the rage among connoisseurs. That attention to detail may be because wine's distinctive notes — say, pear, apple, black currant, clove, tobacco, or leather — bring to mind almost anything but the flavor of grapes. For instance, citrus and floral overtones might distinguish a muscat, undertones of bell pepper are often encountered in a cabernet, grapefruit can be discerned in some sauvignon blancs.

A complex flavor and aroma profile begins with simple sweet-tart grapes. As they're transformed into wine, their natural chemical compounds change. "There's a lot of complex chemistry in wine," Jamie Goode, a British wine journalist and author of "The Science of Wine: From Vine to Glass," writes in an e-mail. Why one grape varietal gives rise to a different flavor and aroma profile than another is "largely because of different levels of precursor compounds, which are then turned into aromatic compounds by the action of yeasts during fermentation," he writes. Differences in acidity, sugars, tannins, and phenolics in the grapes play into the process, he points out.

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Aromatic compounds are among the molecules that give everything from freshly baked bread to sizzling bacon their characteristic scents. In wine, some of these are identical to those found in other substances. Buttery notes in chardonnay, for instance, are the result of an identical molecule found in butter. The compound that gives a peppery bite to syrah is also found in black pepper.

How grapes are processed accounts for complexity in your glass. Yeasts that transform grapes' natural sugars into alcohols and carbon dioxide during fermentation also release their flavor and aroma compounds. "The strain of yeast makes a huge difference to the flavour of the wine," writes Goode. Yeasts native to specific vineyards and wineries produce unique profiles and differ from commercial strains. In some wines, a secondary fermentation changes tart malic acid into smoother lactic acid by means of bacteria, developing unique flavor and aroma compounds along the way.

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Wine aged in oak barrels develops oaky qualities and picks up hints of clove, nutmeg, cinnamon, and vanilla. The age of the barrel, whether it is American or French, and its size affect the wine's character, Goode notes.

Apparently the ability to tease out subtle notes that arise from every vintage doesn't make you a better taster. "Expertise is mainly about cognitive processing of the flavours experienced. Experts aren't usually 'better tasters' in the sense of perceiving more. They're just better able to use the information they get," he writes.

It's all in the way you think about what you're drinking.


Valerie Ryan can be reached at valerie.ryan.j@gmail.com.