RESEARCH
DREW HORTON • ENOLOGY SPECIALIST, HORTICULTURAL RESEARCH CENTER
retained, and all or a portion of the whole clusters are put directly into the fermentation vessel. This contact with the stems allows additional tannins to be extracted, resulting in wines with more intense color, flavor, texture and complexity. In 2021, I collaborated with Dr. Aude Watrelot, Assistant Professor of Enology at Iowa State University (ISU), on a project to produce three experimental wines from Marquette and Frontenac grapes sourced from the Horticultural Research Center and ISU’s vineyards. First, a control batch was created with all the stems removed. Then, experimental batches were made, with both 25% and 50% whole clusters retained. The finished wines were subjected to various analyses to measure and compare the phenolics, tannins and color compounds, and regional winemakers and growers evaluated the wines in 2022. The results showed a preference for the wines made with 50% whole clusters. Chemical analyses revealed much higher amounts of color and flavor (tannin) in the finished wines. With this knowledge, we can now provide recommendations on how to produce better and more popular styles of wines from our University of Minnesota developed grape varieties. Photo by Elise Bremer
Released in 2006 as part of the Horticultural Research Center’s cold-hardy grape research, the red wine grape Marquette has become very popular among Midwest growers and winemakers for a variety of distinctive characteristics — specifically that it can make a dry, balanced red wine similar in character to traditional European reds. Marquette has relatively high amounts of proteins in its juice and pulp, which tend to bind up the tannin and phenolic color compounds (anthocyanins) in Marquette’s resulting wines, often offering lighter color, softer structure and body and a less-complex mouthfeel. So we had to ask: Could there be a way to boost these traits when making Marquette or other Minnesota wines? In the traditional home of pinot noir in Burgundy, France, many winemakers use a technique known as whole-cluster fermentation. In typical red winemaking by contrast, the grape clusters are destemmed, crushed by machinery and fermented “on the skins,” along with the pulp and seeds of the grape, without the stems. The skins and seeds provide the color and tannin compounds that lend most red wines their deep color and complex mouthfeel. But in whole-cluster winemaking, all or a portion of the stems are
John Thull (left) and Colin Zumwalde (right) of the Arboretum’s Grape Breeding and Enology Project deliver whole clusters of grapes from the vineyard to the Horticultural Research Center’s enology lab for evaluation. A R B O R E T U M M AGA Z I N E // D E C E M B ER 2023 • J A N UA RY 2024
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