Slowing down grape ripening boosts flavors prized by winemakers

June 30 (UPI) -- When heatwaves and droughts strike, grapes tend to ripen earlier and faster, yielding less flavorful grapes for winemaking.

Unfortunately, vineyards all over the world are likely to experience longer, hotter and more frequent droughts as Earth's climate warms.

In order to adapt, some winemakers have already begun experimenting with different varieties, but new research suggests growers may also need to adjust their cultivation strategies.

In a new study, published Wednesday in the Journal of Agricultural and Food Chemistry, researchers identified ways to slow the ripening process, yielding more flavorful grapes.

When grapes ripen slowly, sugars and aroma compounds have time to accumulate in the berries, ultimately yielding wine with the floral and fruity notes prized by winemakers and wine drinkers.

Conversely, grapes that ripen faster and earlier tend to yield more alcoholic, less flavorful wines -- duller in color and tainted by notes of cooked fruit.

For the study, scientists altered the care for different rows of Cabernet Sauvignon wine grapes at a commercial vineyard in California's San Joaquin Valley.

Among rows of grapes, researchers created four groups for the experiment: Grape clusters were thinned on some rows, irrigation was increased late in the season on other rows, some rows were both thinned and irrigated, and a group of control rows were left alone.

"The rate of sugar accumulation of grapes was manipulated by varying the crop load and irrigation regime and the development of secondary metabolites was monitored by gas chromatography-mass spectrometry and high-performance liquid chromatography," researchers explained in their paper.

Researchers found that rows with sparse clusters tended to ripen earlier and faster. However, clusters that were intentionally thinned and irrigated experienced delayed ripening, yielding an improved phenolic profile.

Grapes that ripened by slowly as a result of thinning and late-season irrigation boasted higher concentrations of norisoprenoids and terpenes, compounds responsible for pleasant floral and fruity wine notes.

The same grapes had lower levels of six-carbon aldehydes and alcohols, the compounds associated with less desirable flavors.

"The longer growing time improved the quality of grapes for winemaking," according to the researchers. "But these adaptation strategies should be monitored over several years before changes are made to current practices."