By Dr. Aude Watrelot –
My lab focuses on understanding and improving viticultural and winemaking practices to apply on cold hardy grapes and wines with a specific focus on phenolic compounds. These compounds are responsible for many features in wines such as color stability, reduction of the risks of oxidation and improvement of wine aging and mouthfeel (Watrelot, 2021; Watrelot & Norton, 2020). This year my lab focused on various applied research aligned with Extension and outreach work to provide tools and knowledge to you, as grape and wine industry members.
Some ongoing applied research projects
- Effect of leaf removal on phenolic compounds in Iowa ‘Marquette’ grapes and wines.
This project started in 2020 at the ISU Horticulture Research Station and was carried out over two years. My undergraduate and graduate students, Lucas Buren and Yiliang Cheng, were involved in the leaf removal process of Marquette grapevines trained in a Single High Wire trellis system after fruit set and at veraison in 2020 and 2021. The goal of this project is to evaluate the impact of leaf removal on Marquette grape chemistry during berry development, during ripening, and on the wine produced. Previous studies have been carried out using the leaf removal practices on interspecific hybrid varieties, including Marquette in Wisconsin (Riesterer-Loper et al., 2019; Scharfetter et al., 2019), for example, but never under these conditions in Iowa where the overall environment is different. We gathered the weather data, the basic chemistry parameters of grapes from fruit set to harvest maturity as well as total content of phenolic compounds, including tannins and anthocyanins, and we are currently analyzing those data. The chemistry of grapes was highly impacted by the growing season in 2021, where the degree Brix and color intensity were higher and TA was lower than in 2020 at harvest. The effect of leaf removal was not significant on the basic chemistry in 2021, and tended to reduce the level of organic acids in 2020. Also, no effect of leaf removal was observed on the total phenolic compounds and tannin content at veraison and harvest. Our results suggest that other viticultural practices may be more suitable to cold-hardy varieties to improve phenolic compounds and reduce grape acidity. This project is still ongoing.
- Could we extract more phenolics by applying Accentuated Cut Edges and/or enzymes?
This project also started in 2020 with the participation of Fireside Winery ,Tassel Ridge Winery, and the Midwest Grape and Wine Industry Institute. The goal of this project, which is part of Yiliang’s PhD project, is to better understand the extraction of phenolic compounds, especially tannins, from cold-hardy grapes in red wines. Most of the winemaking practices are based on Vitis vinifera practices, which is not the most appropriate for the cold-hardy grapes that have very different chemistry. Tannins content is low in cold-hardy red wines, which leads to these wines being more prone to oxidation, and unbalanced with acidity that dominates the overall wine perception. My lab focuses on techniques to improve this tannin content and therefore the overall wine quality. The use of Accentuated Cut Edges (Kang et al., 2020; Sparrow et al., 2016) started in 2019 by the MGWII and Fireside winery on Marquette musts. We decided to focus on different timing of application of this ACE technique, which is a “blender” cutting skins into small fragments, to improve the extraction of tannins from grape skins. After applying this technique at crushing and 24hr prior to pressing, we observed an increased color intensity at crushing right after ACE application with an improvement of phenolic compounds content. We therefore decided to compare the use of ACE to the addition of enzymes (pectinases) at crushing on Marquette phenolic compounds content. The ACE treatment seemed to improve the phenolic compounds content in Marquette wines at bottling compared to using enzymes and the control. Yiliang is currently working on the application of ACE in addition to two different enzymes on Marquette wine chemistry, as well as on the application of ACE on other Marquette grapes and Frontenac grapes. After a few months of aging, the next steps with the wines made using these techniques will be to conduct a sensory evaluation, and to charcaterize polysaccharides in wines, as polysaccharides could help explaining the low tannins content in cold-hardy wines.
- Impact of the addition of whole clusters in ‘Marquette’ and ‘Frontenac’ wine.
The addition of whole clusters as a prefermentative technique on Pinot Noir has shown promising results for the wine tannin content and wine aromawhen using a ratio of 50% and 100% whole clusters (Casassa et al., 2021). We therefore decided to evaluate the impact of the addition of whole clusters on ‘Marquette’ and ‘Frontenac’ musts on the extraction of tannins from stems and improve the grape aroma characteristics. This project is a collaborative project with Drew Horton from the Univeristy of Minnesota focusing on Frontenac and Marquette from Iowa and Marqeutte from Minnesota. This project is ongoing and chemical and sensory data will be gathered and compared to evaluate the impact of different percentage of whole clusters additon on wine quality.
- How cold-hardy red wines change over time?
Wines produced in Iowa can sometimes be sold to consumers a few years after their production, but the quality decreases over time. In this project, red wines aged from 1 to 5 years, in addition to their chemical and storage details, were collected from three wineries in 2021. The goal of this ongoing project is to identify the evolution of cold-hardy red wine quality over time, and help develop knowledge and tools to improve red wine quality during aging.
- How to add a value to the common waste, grape pomace?
This project was explained in the newsletter article of June 2021.
Educational tools with and for the grape and wine industry
As the result of a survey about the educational needs of Iowa grape and wine industry I developed in 2019, some of the main concerns that you have is related to low number of consumers visiting your wineries, as well as not enough information available for you on viticultural and winemaking practices. Here is a list of workshops, webinars, and field days that took place in 2020 or 2021, with links for you to have access to the info. If you missed them in 2021, do not worry, they are going to be offered in 2022. Stay tuned!
- Education of wine consumers towards Iowa grapes and wines. An Iowa wine brochure is available for free to download on the ISU Extension store (https://store.extension.iastate.edu/product/16322) . This brochure is to provide more information to consumers when they come to visit your place.
- Grape maturity field day. This field day was offered at the ISU Horticulture Research Station in August 11 2021. Feel free to go on the ISU Extension store for some fact sheets about grape maturity evaluation (https://store.extension.iastate.edu/product/16073) .
- Updates on research and winemaking topics to grape and wine industry members. With my colleague, Drew Horton from the University of Minnesota, we developed the ISU/UMN Research and winemaking webinar series in 2020 on various topics involving an industry partner and a researcher. If you were not able to attend, the recordings are available on YouTube: (https://www.youtube.com/playlist?list=PLfUP_JVYHQtOci2Uy7DJYx5HCtAP5COTX).
- Newsletter articles of specific topics. The updates on some specific research and winemaking are part of my newsletter articles. Feel free to read them throughout the MGWII website: https://www.extension.iastate.edu/wine/ or Watrelot’s lab website: https://faculty.sites.iastate.edu/watrelot/
If you have any suggestions or questions about the research/winemaking topic, feel free to contact me at watrelot@iastate.edu.
References to learn more:
Casassa, L. F., Dermutz, N. P., Mawdsley, P. F. W., Thompson, M., Catania, A. A., Collins, T. S., Ashmore, P. L., Fresne, F. du, Gasic, G., & Peterson, J. C. D. (2021). Whole Cluster and Dried Stem Additions’ Effects on Chemical and Sensory Properties of Pinot noir Wines over Two Vintages. American Journal of Enology and Viticulture, 72(1), 21–35. https://doi.org/10.5344/ajev.2020.20037
Kang, W., Bindon, K. A., Wang, X., Muhlack, R. A., Smith, P. A., Niimi, J., & Bastian, S. E. P. (2020). Chemical and Sensory Impacts of Accentuated Cut Edges (ACE) Grape Must Polyphenol Extraction Technique on Shiraz Wines. Foods, 9(8), 1027. https://doi.org/10.3390/foods9081027
Riesterer-Loper, J., Workmaster, B. A., & Atucha, A. (2019). Impact of Fruit Zone Sunlight Exposure on Ripening Profiles of Cold Climate Interspecific Hybrid Winegrapes. American Journal of Enology and Viticulture, 70(3), 286–296. https://doi.org/10.5344/ajev.2019.18080
Scharfetter, J., Workmaster, B. A., & Atucha, A. (2019). Preveraison Leaf Removal Changes Fruit Zone Microclimate and Phenolics in Cold Climate Interspecific Hybrid Grapes Grown under Cool Climate Conditions. American Journal of Enology and Viticulture, 70(3), 297–307. https://doi.org/10.5344/ajev.2019.18052
Sparrow, A. M., Holt, H. E., Pearson, W., Dambergs, R. G., & Close, D. C. (2016). Accentuated Cut Edges (ACE): Effects of Skin Fragmentation on the Composition and Sensory Attributes of Pinot noir Wines. American Journal of Enology and Viticulture, 67(2), 169–178. https://doi.org/10.5344/ajev.2015.15094
Watrelot, A. A. (2021). Tannin Content in Vitis Species Red Wines Quantified Using Three Analytical Methods. Molecules, 26(16), 4923. https://doi.org/10.3390/molecules26164923
Watrelot, A. A., & Norton, E. L. (2020). Chemistry and Reactivity of Tannins in Vitis spp.: A Review. Molecules, 25(9), 2110. https://doi.org/10.3390/molecules25092110