Cool summer to benefit Indiana grapes, future wines

September 3, 2013  

WEST LAFAYETTE, Ind. - This summer's mild temperatures and modest rainfall have been good for Indiana's wine grapes, which could lead to more flavorful, aromatic wines, say members of the Purdue Wine Grape Team.

Average temperatures in July and August were slightly cooler than normal, conditions that allowed ripening grapes to accumulate sugar and maintain acid levels. An extraordinarily dry August also was beneficial, as heavy rainfall can cause ripened grapes to split, leading to pest damage and disease.

"We've had really moderate conditions, and that helps improve fruit quality," said viticulture specialist Bruce Bordelon. "Cooler weather leads to higher sugar content and higher acidity, yielding a better balance overall. Our mid- and early-ripening varieties should do really well."

Bordelon said weather has a tremendous influence on veraison, the ripening process in which grapes transform from hard, opaque green berries into soft, translucent fruit. Temperature and rainfall during ripening can determine the character of future wines.

"The most important time frame for fruit and wine quality is those last four weeks before harvest," he said. "That's when the berries go through the ripening process. The conditions during that time - especially the temperature - are what really affect wine quality, not just in terms of sugar-acid balance but flavor and aroma content as well."

Grape growers in the southern part of the state gained the most from the cool summer, as they have completed their harvest of early- and mid-ripening varieties, but north-central Indiana still stands to benefit, particularly with its mid-ripening grapes, said Bordelon.

"Traminette and Vignoles should come in great this year," he said. "They've enjoyed perfect conditions and should develop really interesting flavor and aroma compounds." Traminette is Indiana's signature wine grape variety, and Indiana-grown Vignoles wines have won Wine of the Year at the Indy International Wine Competition, conducted by the Purdue Wine Grape Team, for the past two years.

Bordelon's only concern is that there will not be enough remaining warm weeks for some grapes to fully ripen, especially late-ripening varieties grown in the northern part of the state.

"The cooler weather could be a downside for some of the red varieties like Chambourcin and Cabernet Franc," he said. "If we don't get enough heat, they'll retain some herbaceous characteristics. That's my only concern for this year."

Enologist Christian Butzke agrees that the milder summer should have a positive impact on Indiana's grapes.

"Having a cool summer facilitates retention of acids, and it's the acidity - that crispness - that makes many wines from the Midwest so special," he said. "Our summer has been nice: mild temperatures and not too much rain. I think we can expect a high quality crop and really complex, interesting wines coming from that later on."

Though optimistic, Butzke cautions that Indiana weather can change abruptly, as it did in late August when temperatures rose into the 90s. Excessively hot days followed by warm nights can cause grapes' acid content to decrease quickly, resulting in less tart, more  "flabby" wines.

Butzke says the advantages of this summer's weather will not be seen until the wines have been aged and released: usually about a year for white wines and two years for red wines.

"In the end, all that counts is what the wine tastes like once it's in the glass," he said.

To learn more about Indiana grapes and wines, see "Through the Grapevine," a multipart, multimedia series by the Purdue University Department of Agricultural Communication premiering Sept. 10 at

Writer: Natalie van Hoose, 765-496-2050, 

Sources: Bruce Bordelon, 765-494-8212,

Christian Butzke, 765-494-6500,

Related website:

Indiana State Climate Office


 A link to a video clip of Bruce Bordelon talking about the effects of a mild summer on Indiana's wine grapes is available at 


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Note to online editors: A link to a video clip of Purdue viticulture specialist Bruce Bordelon discussing the effects of mild summer temperatures on Indiana's wine grapes is at the bottom of this news release. The video can be embedded in your website.

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