Viticulture is important to Michigan’s economy, but the state’s cool climate makes for a short growing season (May-October), which can present challenges for growers — limited fruit ripening, damage to vines, delayed fruit maturation — especially when it comes to red wine grapes.
“Michigan is really a different place to grow grapes than any other place in the world,” said Paolo Sabbatini, associate professor in the Michigan State University (MSU) Department of Horticulture. “However, we have the potential to produce very outstanding wines. Unfortunately, the season variability and climate challenges often limit this.”
Sabbatini, along with Ilce Medina Meza, assistant professor in the MSU Department of Biosystems and Agricultural Engineering, is leading a three-year, $500,000 U.S. Department of Agriculture National Institute of Food and Agriculture (USDA NIFA) project testing alternative canopy management strategies to help Michigan wine producers grow grapes with high-quality aroma, color, bitterness and mouthfeel properties from the most important red cultivars planted in Michigan: pinot noir, cabernet and merlot.
The canopy of a grapevine is the part that’s visible above ground. It includes the leaves, shoots and the trunk of the vine.
“Canopy management is how you manage the canopy structure during the summer in a way that can really speed up fruit maturation,” Sabbatini said. “In Michigan, we need to be able to ripen the fruit at a lower temperature during the summer in a shorter time.”
Applying Early Leaf Removal
Sabbatini and Medina Meza are implementing a novel technique called early leaf removal, a variation of a classical cool-climate viticulture technique used in regions such as northern Germany and New Zealand. Instead of removing leaves at the end of the growing season, as is done in traditional leaf removal, Sabbatini and Medina Meza will remove them at the beginning.
When berries first bloom, leaves are removed using an air pulse leaf remover. The machine, which has been used in Europe, but is relatively new to the U.S., uses powerful jets of compressed air to shred canopy leaves. The removal of canopy leaves allows for clusters of grapes to be exposed to more light and warmer temperatures. This causes heat stress, which can result in grapes ripening earlier. In order to defend against heat stress, grapes will produce tannins, antioxidants and other compounds that are found in finished wines.
“If you attack the cluster with high temperatures and a lot of light at the beginning of the season, you improve fruit quality a lot: The grapes ripen earlier, and they have more sugars, they have more color, they have all the compounds that we like in wine,” Sabbatini said.
Assessing Grape Quality
Medina Meza is researching how early leaf removal contributes to improved sensorial properties, mouthfeel, color, and increased antioxidant levels of red wine grapes to enhance overall quality.
“The cold weather and short viticulture field season in Michigan is challenging for the accumulation of compounds key for growing wine grapes,” she said. “The best way to evaluate this accumulation is through metabolomics.”
Metabolomics is the comprehensive analysis of small molecules in a biological system. These systems include cells, organisms, plant tissues and food.
“By using metabolomics, we can profile the specific of compounds or metabolites, that have been accumulated in the grapevine after early leaf removal,” Medina Meza said. “We can also understand more about how light and temperature exposure affect these compounds.”
Part of Medina Meza’s work on this project focuses on grape specialized metabolites (GSMs), compounds that provide a specific color for the final wine product.
“GSMs are accumulated in the skin of the grape, and they provide this beautiful red color that is needed for the next step, during the wine making production,” she said. “So, these will enhance during fermentation that we have in this beautiful red wine as the final product.”
Power of Partnerships
On-site research for this project will be conducted at Brys Estate Winery in Traverse City, Mich. Samples of flowers, leaves and fruit from Brys Estate will be brought back to a lab, where Medina Meza will analyze tests to see the impact early leaf removal has on the compounds in the grapes.
“This is a perfect project to demonstrate the importance of working across disciplines. Paolo is applying the agricultural practices, while I’m working to understand more about the physiology of the grapes,” Medina Meza said.” “It’s a great thing to bring together different expertise to see how the plants adapt or react to early leaf removal.”
Sabbatini and Medina Meza’s research has strong support from the Michigan wine industry.
“Producing better grapes consistently means producing better wine. That means selling more wine from Michigan,” Sabbatini said. “This project is very important to growers. At the end of the project, we’ll have strong, solutions driven recommendations on how to manage canopies of the vines in Michigan’s climate.“
“Every year, growers see new improvement, more yield in the field, they see more red wines as the final product,” Medina Meza said. “I think we are making a huge impact in that regard, especially if this technique can be translated to other cool climate regions around the world, including the rest of the U.S. Midwest.”
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