Red wine fermentation alters grape seed morphology and internal porosity

Authors: GILLISPIE, ELIZABETH - Washington State University; MILLER, KONRAD - Solugen; McElrone, Andrew; BLOCK, D - University Of California, Davis; Rippner, Devin

Submitted to: American Journal of Enology and Viticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2023
Publication Date: 10/2/2023
Citation: Gillispie, E.C., Miller, K.V., McElrone, A.J., Block, D.E., Rippner, D.A. 2023. Red wine fermentation alters grape seed morphology and internal porosity. American Journal of Enology and Viticulture. 74(2). Article 0740030. https://doi.org/10.5344/ajev.2023.23025.
DOI: https://doi.org/10.5344/ajev.2023.23025

Interpretive Summary: During red wine fermentation, all grape parts undergo big physical and chemical changes. Past research has focused on the chemical processes that influence the release of grape compounds like tannins from seeds which are important for wine taste, texture, and quality. However, little research has been conducted to understand how the seeds might physically change during fermentation which could also change what ends up in the wine. Recently, USDA researchers used X-ray imaging, high energy penetrating picture taking, to quantify for the first time how fermentation changes grape seed internal parts, which could affect important chemical processes during wine making. These results will help wine makers and scientists better understand some of the physical processes occurring inside of grape seeds during wine making and using the byproducts for value-added food ingredients and dietary supplements.

Technical Abstract: During wine fermentation, grape berry components, including seeds, undergo extensive physical and chemical change, which result in the release of flavonoids, such as tannins, from seeds into wine. Understanding changes in seed morphology during fermentation is crucial for aiding in the development of accurate prediction models for flavonoid extraction during winemaking, which enhances fermentation management and ensures consistency in wines from year to year. High resolution X-ray micro-computed tomography (micro-CT) was used to investigate the effect of red wine fermentation on changes in grape seed morphology. Using a Pytorch based implementation of a Fully Convolutional Network with a Resnet-101 backbone for semantic segmentation of micro-CT images, we quantified extensive alteration to grape seed structure during fermentation. Results from image analyses revealed the development of a pore network breaking apart the endosperm of the seed by the end of fermentation, leading to an increase in surface area. Such alterations were not previously reported and could enable transport of seed flavonoids from inside the endosperm and inner integument to outside the seed. Further research on the physical processes occurring in seeds during wine fermentation is necessary to build better physiochemical models.