The Effects of Cluster Light Exposure, Timing of Leaf Removal, and Crop Load on Rotundone Development in Noiret Grapes and Wine
By: Laura Homich
What is Rotundone?
Rotundone is a hydrophobic sesquiterpenoid ketone found in the grape skin [1, 2]. In 2008, this compound was identified as the aroma compound which imparts the desirable spicy black pepper notes associated with Australian Shiraz [3, 4]. Rotundone has been identified in red varieties Schioppettino, Mourvèdre, Durif, and Vespolina as well as the white variety Grüner Veltliner . Additionally, rotundone was observed in several herbs and spices (nut grass, marjoram, rosemary, saltbush, geranium, thyme, basil, and oregano) and was found at the highest levels in white and black pepper .
Rotundone Sensory Characteristics
Most varietal aromas are created by a combination of several different chemical components. In contrast, rotundone is one of the few known aroma impact compounds, having the ability to impart a characteristic aroma with a single compound . The potency of this odorant results in a sensory detection threshold of 8 ng/L in water and 16 ng/L in red wine . Interestingly, sensory studies have shown that 20% of consumers were not able to detect this compound at 4000 ng/L (250 times the detection threshold), suggesting that two consumers drinking the same wine may have drastically different sensory experiences .
Goals of the Study
Several Pennsylvania growers have expressed interest in learning more about pepper aroma variation through viticulture practices as well as consumer preferences. Previous studies have found that higher rotundone concentrations are found in cool climate regions ; therefore, this characteristic pepper aroma is prevalent in some Pennsylvania grown varieties, notably Noiret. This work is first set out to determine the presence of rotundone in the Noiret variety. The effects of the timing of leaf removal (berries pea-sized versus post-veraison), cluster light availability, and crop load will also be investigated. Sensory analysis will be carried out to determine consumer sensory preferences of wine made from the leaf removal and sun exposure treatments.
A field trial has been established at the Cornell-NYSAES research station in Geneva, NY in collaboration with Dr. Justine Vanden Heuvel. Noiret berry samples were collected at four time points between pre-veraison and harvest. Canopy density was measured at three time points throughout the same period. Hail damage was observed on July 31st, resulting in injury on some of the exposed clusters. At harvest (October 28th), crop yield data was recorded for each treatment and berry samples were collected for Brix, pH, TA and rotundone analysis.
The Noiret grapes were crushed and destemmed according to treatment. Each treatment was split into two replicate fermentations, and each fermentation was chapitalized to reach a final Brix of 21. At the completion of primary fermentation, the wines were pressed and inoculated for malolactic fermentation. At that time, a strong black pepper aroma was noted in all treatments.
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Special thanks go to Dr. Justine Vanden Heuvel, Steve Lerch, and the team at Cornell University for allowing us to use the NYSAES Noiret plot for this study as well as assisting in field measurements. Thank you to Don Smith, Denise Gardner, and members of the Centinari, Elias, and Gardner labs for assisting with data collection, harvest, and winemaking.
Laura Homich is a M.S. Candidate in Food Science under the direction of Dr. Ryan Elias and Dr. Michela Centinari.