In its 2020-21 fiscal year, the Oregon Wine Board of Directors granted $350,000 to researchers for eight projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is part of a series to let industry members know about the status of these projects.
Dr. Federico Casassa, associate professor of wine sensory in the Department of Wine and Viticulture at California Polytechnic State University San Luis Obispo, is principal investigator on the project described below. His department colleague Dr. Jean Dodson Peterson, associate professor of viticulture, is co-PI on this project. They have prepared the update below.
Chemical and sensory effects of intrinsic variations of berry size in Vitis vinifera L. cultivars
This project focuses on V. vinifera L. cv. Pinot noir berry size, as well as associated wine sensory and chemical attributes. The objectives are:
- Classify and record intrinsic variations in berry size for Pinot noir clones. We will use a berry sorting device that has been designed and trialed in-house at Cal Poly to sort berries of Pinot noir into different class size categories. Several methodologies have attempted to classify Vitis vinifera L. berries, including segregation by berry equatorial diameter (Mirás-Avalos et al. 2019, Xie et al. 2018), berry fresh weight (Chen et al. 2018), and berry density and sugar content (Rolle et al. 2015). However, these aforementioned methodologies are limited by the number of berries that can be practially collected and thus winemaking is not possible. In the present work, we propose the segregation of berries by diameter using a large mechanical device that allows collecting berries in the quantities required for winemaking purposes.
- Explore winemaking practices to artificially manipulate berry size to adjust for size related concerns, including saignée (bleed-off), dilution, and addition of extra fermentation solids. Winemakers traditionally compensate large berry size by performing the practice known as saignée or bleed-off (Sacchi et al. 2005). Likewise, when fruit is considered overly concentrated or with sugar levels that would prevent the completion of alcoholic fermentation, water is added, and dilution is presumed (Harbertson et al. 2009). However, the effects of saignée on large berries is largely unknown, and the same is true for water additions performed on concentrated berries, which typically show relatively lower berry size. The present experimental design attempts to improve our understanding on the effects of saignée and water adds on different berry size categories to eventually provide recommendations on the validity and timing of these winemaking practices.
- Analyze phenolic composition, chromatic, and aroma composition of wines made from berries of different class sizes. Once separated by size as a function of clone, analytical analysis will be performed on both the grapes and finished wines to determine phenolic composition and chromatic characteristics. Aroma composition will be also measured by GC-MS analysis.
- Perform descriptive analysis using a trained sensory panel for the wines made from berries of different size classes. We will organize and execute a formal descriptive sensory analysis by conveying a panel of wine professionals. Previous published work on the effects of berry size have focused on the chemical composition of the grapes (Rolle et al. 2015), and the resulting wines (Chen et al. 2018, Xie et al. 2019), but sensory analysis has been hampered by impossibility to produce wine at larger volumes. The proposed experimental design allows to account for wine production in sufficient quantities to allow formal descriptive analysis, as previously detailed (Lawless & Heymann 2010). Chemical and sensory measurements will be jointly analyzed using multivariate analysis techniques, including principal component analysis.
Importance to the Oregon wine community:
The understanding gained from completing the objectives will assist Oregon winemakers in clonal selection and winemaking techniques in Pinot noir for management of berry size related chemistry issues.
The wine industry has accepted the paradigm that larger berries will necessarily produce a poor-quality wine, and that smaller berries will produce a high quality wine. This is because solutes of sensory relevance (anthocyanins, responsible for wine color; tannins, responsible for wine tactile sensations such as astringency; aroma precursors responsible for production of secondary and tertiary aromas) are located in the grape solids (skins and seeds). Also, small berries have a solid (i.e. skins and seeds) to liquid (i.e. pulp) ratio much greater than that of comparatively larger berries. Therefore, smaller berries should be more concentrated in solutes of sensory relevance than larger ones.
However, berry size is under genetic control, and there are grape varieties—and clones—with inherently larger berries while other varieties exist that have inherently smaller berries (Fernandez et al. 2006; Houel et al. 2013). There is to date very limited information on the chemical and sensory implications caused by intrinsic variations in berry size. This project presents an experimental design aimed at assessing the separate effects of intrinsic variations in berry size as well as that of an “artificial manipulation” of berry size achieved through the application of selected winemaking techniques (i.e. saignée and must additions). To that end, berry populations of several clones of Pinot noir with contrastingly different berry sizes, will be used.
The results generated by this project could help both viticulturists and winemakers to understand the chemical and sensory implications of berry size variations, as well as the feasibility of applying specific winemaking practices tailored to each clone.
Progress so far:
The project examined variation among three Pinot noir clones (2A, 96 and 115). The three clones were selected to capture the widest possible range of berry sizes within Pinot noir clones. Grapes were harvested at a target Brix of 24.5 ± 0.5 normally indicated for standard (commercial) winemaking practices for red wines (Casassa et al, 2021). Once harvested, grapes were immediately precooled to reduce field temperature to a target of 12 ± 1 °C. After attaining target temperature, grapes were gently destemmed and subsequently segregated into 4 different diameter classes (8 mm, 10 mm, 12 mm, 14 mm) by forcing the destemmed grapes to fall by gravity into a series of sieves of berry sorting device. After berry sorting using this device, berries of each class were manually crushed and made into wine under controlled conditions.
Additionally, selected berry classes of these two varieties were also processed with specific winemaking techniques, including saignée and water-back. Wines were made following standard winemaking practices, as previously described (Casassa et al. 2013a), with the following modifications. Fermentations were carried out in 12L food-grade glass fermenters. Each treatment was conducted in triplicate for each clones examined. Wines were produced at the Pilot Winery of the Wine & Viticulture Department in Cal Poly San Luis Obispo. Briefly, individual fermentations, consisting of 10 ± 0.1 kg of berries each, were performed in triplicate for each variety and including as treatments: the 4 different diameter classes in addition to an unsorted treatment (berries not classified by diameter as they normally occur within the grape cluster).
In addition to these berry size treatments, two more “compensated” treatments will be included to artificially simulate differences in berry size. These treatments were imposed by performing saignée or must additions based on either differences in berry fresh weight or differences in the solid to liquid ratio, as applicable. Ferments containing berries of the 12 mm class were subjected to saignée at the same percentage rate that the difference (in percentage) in berry fresh weight (or solid to liquid ratio), between the 12 and 10 mm classes. Ferments containing berries of the 10 mm class were submitted to must addition at the same percentage rate that the difference (in percentage) in berry fresh weight (or solid to liquid ratio), between the 12 and 10 mm classes.
The initial analysis of the Pinot noir fruit indicate a variation in the accumulation of soluble solids and subsequent harvest dates when at full maturity (25 Brix). Statistical variation has also been identified among clones for leaf area index, cluster count, yield, weight/cluster and pruning weight. We also see variation in the fresh weight distribution of berry class as a function of clone. Clone 115 had the highest percentage of 12 mm berries and the lowest percentage of 8 mm berries. Clone 96 had the highest percentage of 14 mm berries. Alcoholic fermentation progressed significantly slower in wines made out of raisins berries, and this is expected due to significantly higher sugar content on raisined berries. Differences in basic chemistry were primarily due to clonal effects, with lesser effects due to berry size treatments.
Phenolic and color analyses are currently underway, but some preliminary results are already available. We found enhanced color and phenolic extraction in wines made out of raisins in the case of clone 115. However, there was little effect of berry size on color extraction when color extraction patterns of unsorted, 10 mm and 12 mm berry wines were compared in the case of clone 115. Also in this clone, the compensated treatments (saignée performed to 12 mm berries and juice added to 10 mm berries) showed that adding juice to clone 115 caused dilution of color, whereas saignée mimicked the extraction seen in 10 mm berries. This suggests that saignée could be a feasible technique to be applied to Pinot noir clone 115 when climatic or viticultural conditions are conducive to larger than average berries.
However, this trend was not observed in the case of the wines of clone 96. In these wines, there was an effect of berry size on color extraction, with ferments from smaller berries producing darker wines. Intrestingly, the compensated treatments (saignée and juice add) did not have a significant effect on color extraction for clone 96, suggesting that the effect on phenolics and color of winemaking treatments that affect the solid to juice ratio in Pinot noir may vary according to the specific clone. These analyses are currently underway for the remaining clone, 2A.
The project will continue for a second year and expand to include vine gas exchange parameters. The 2020 wines will complete phenolic and color analysis and sensory evaluation will commence. The 2021 fruit will be processed and analysis will begin with sensory evaluation the following year.
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