Managing Protection of Varietal Aromas From Wine Oxidation

In order to investigate the reactions of quinones with unknown nucleophiles to further understand how quinones react in wine. The quinone reaction products are investigated by Q-TOF using 13C6 labels. Since the labeled compound is expensive, we used the unlabeled catechol (12C6) first to determine the levels of 13C6 labels we needed, the incubation time, and the Q-TOF method development. We have set up a list of the products from quinone with the known nucleophiles and optimized the analysis method to maximize the numbers of the detection of these known products. Considering the total amount of catechols, such as caffeic acid, catechin, cyanidin, are around 2g/L for red wines and 0.5g/L for white wines and the expecting detection limit of the product is around 2 mg/L, 0.1g/L quinone was added to wines and the level was confirmed by the trials. The incubation time was also tested and finally chosen as 2 hours.

Chiral Terpenes – Quantitation, Threshold Determination and Sensory Impact on Aromatic White Wines

The specific accomplishment of the last year for this project was the development of a quantitative method using MDGC to measure chiral terpenes in white wine. Two hundred and three white wine samples, Pinot Gris and Riesling with diverse residual sugars had been already collected from different places of origin all over the world. Wines were donated from top wine companies from New Zealand, New York, Australia, Germany, Oregon, Washington, France, to name a few. Fifteen chiral mono-terpene compounds were collected from head space solid phase micro-extraction coupled with multidimensional GC-MS with stable dilution isotope quantification analysis. Results for the Pinot Gris wines are presented in this report. In short here were difference sin chiral terpene content between the wines. Additional differentiation was established for place of origin of Pinot Gris wines based on chiral terpene content.

Understanding Pinot Noir Grape and Wine Aroma Composition as a result of changes in Vine Balance, year 1 of a 3

Vine balance is important in determining fruit and wine composition. Excessive canopy density is known to produce unbalanced musts, resulting in poor wine quality. In Oregon, crop thinning is normally conducted between fruit set and lag phase to increase the leaf area: fruit weight ratio in order to prevent over cropping, as well as to improve fruit size and composition. Earlier studies have shown that cluster thinning reduces fruit yield and increases the berry weight, soluble solids, and color of table grapes. However, the impacts of the timing and severity of cluster thinning on subsequent berry growth and fruit flavor composition has not been widely investigated. The main objective of the present study was to evaluate such effects in association with grape and wine aroma composition in Pinot noir grapes and wine. Preliminary results indicated that crop thinning had very limited impact on the grape major volatile composition analyzed in 2011 and 2012. However, the composition of other minor and important compounds, such as methoxypyrizes, are still under investigation.

Judging Wine Quality: Do We Need Experts, Consumers or Trained Panelists?

The overall objective is to determine if quality can be reliably evaluated by wine consumers, wine aficionados and/or wine experts and what their quality scores actually mean relative to the intensities of the sensory attributes we get from trained panels, and the liking scores we get from wine consumers. To choose wines with different quality levels we used the judging scores assigned to 27 Cabernet sauvignon wines in the 2012 California State fair judging competition.

At this competition Cabernet wines are divided into 9 regions. Within each region we picked the wine with the highest score (usually a gold medal wines), the wine with the lowest score (a wine that did not medal) and then a wine with a score as close to the mean between the highest and lowest score. The 15 descriptive analysis panelists (10 males, 22-72 years old, average age 37 yrs, median 31 yrs, standard deviation 17 yrs) were recruited from the students, staff and faculty of the Departments of Viticulture & Technology, Food Science & Technology, and Aerospace Engineering. They participated in 6 1-hr training sessions to collect, generate and obtain consensus on 21 aroma, 3 taste and 3 mouthfeel attributes. Their evaluation of the wines, in triplicate will be complete on 2/7/13. The consumer hedonic evaluation, using the 9-point hedonic scale has been scheduled for February 2, 2013 – we are aiming to have about 192 participants and each participant would evaluate 6 wines. Thus each of the 27 wines would be evaluated by 42 or 43 consumers.

Evaluating the Effects of Sterile Membrane and Other Filtration on the Sensory and Chemical Properties of Wine

The goal of our project is to evaluate the effects of sterile membrane and other filtration on the sensory and chemical characteristics of wine. To do this, we have filtered two red wines, a Cabernet Sauvignon and a Merlot, and one white wine blend through 0.45 µm PVDF and PES membrane filters and compared the sensory and chemical characteristics of these wines to unfiltered control wines. Treatments were expanded with the Merlot and white blend to also examine the effects of a pad filter and cartridge depth filter used as prefilters. We have examined changes in dissolved oxygen content, tannin content, and color during the course of filtration and found only minor changes. Sensory panels were trained for each of these wines and each of the treatments evaluated immediately after filtering and then on a regular basis for 9 weeks (for the Cabernet), 24 weeks (for the Merlot), and 20 weeks (for the white blend). While all three wines changed significantly over time in the bottle, very few significant differences were observed in aroma or mouthfeel between filtration treatments. In other words, our results thus far indicate limited impact of sterile filtration on the sensory or chemical properties of the wine, regardless of the type of filter material used. We did observe a small decrease in tannin and astringency with the pad filter for the Merlot wine, but we are continuing to investigate the significance of this change. In addition, we are preparing to evaluate the effects of filtration of both a red and white wine using a cross-flow filter, as well as evaluating the effects of the associated pumps, during the next three months.

Production and Management of Aroma Compounds by

The yeast Dekkera/Brettanomyces is commonly found in wines and is responsible for a wide array of characteristic odors. The primary aim of this project is to illuminate the factors that are most important in the survival and growth of Brettanomyces bruxellensis in wine and how these factors influence the production of off odors. The role of growth in wine and defined medium on the metabolic state of Brettanomyces cells was investigated. Three strains were analyzed during growth over 54 days in wine and a defined medium. Differences in the metabolic profile were determined and correlated with each variable, strain and growth medium. Ten Brettanomyces strains for the production of odor active compounds in defined medium with specific substrates added were also analyzed. These ten strains were chosen from approximately 100 Brettanomyces strains that were screened for differences in aroma production. The ten strains were selected for lower levels of odor production both in defined medium and wine. The analysis of the metabolic profile of Brettanomyces in wine and defined medium revealed some expected differences in lipid and carbon metabolism. Unexpected differences in amino acid and nitrogen compounds were also found. Fatty acids and lipids are involved in ethanol tolerance and general stress tolerance. The changes seen in fatty acid metabolism suggest the cells are altering membrane lipids in ways designed to stabilize the membranes under stress conditions. Fatty acids such as isovaleric and isobutyric acid are also involved in off-aroma production so this adaption to stress may be correlated with off-character formation. Proline and urea were uniquely increased in wine-grown cells. The increase in these nitrogen compounds could be due their use as nitrogen sources but proline may play another role as well. Plants and bacteria use proline as an osmoprotectant. It may play a similar stabilizing role in Brettanomyces in wine. An increase in metabolic compounds involved in the use of pentose sugars was also found in wine grown cells. Differences between strains were also observed. Surprisingly there was a consistent and significant trend showing that strain UCD 2091 was different from strains UCD 2082 and UCD 2807 in multiple metabolic pathways.

Metabolic Profiling of Grape and Wine Aromas

Most aroma compounds exist in grapes as glycosidically bound precursors and the aglycones (‘free’ aroma compounds) are released by enzymatic or acidic hydrolysis during crushing, fermentation and wine aging. We evaluated procedures for measuring the glycosidically bound volatiles using both acid and enzyme hydrolysis conditions followed by analysis of the free volatiles by Headspace Solid-Phase-Microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Acid hydrolysis of a mixture of standard compounds at pH 1 and 100º C for 1 hour released 20-60{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the bound volatiles, however, these conditions also resulted in significant degradation (>50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}) of the free volatiles. Enzyme hydrolysis was generally more effective at releasing glycosidically bound compounds with minimal artifactual changes in the concentrations of the free volatiles. However, esterase and oxidase activity was still observed resulting in artifactual degradation of the free volatiles. Most previous procedures for evaluating volatile glycosides employ an initial sample preparation step using column chromatography to isolate the glycoside fraction from the grapes prior to hydrolysis and analysis of the free volatiles. We observed that different types of sample preparation columns were not equally effective at retaining the glycosides and no column-type was effective for all the glycosides in our mixture. Using optimized conditions obtained from the previous studies with model systems, we compared direct enzyme hydrolysis of Cabernet Sauvignon and Chardonnay grape homogenates with and without prior isolation of the glycoside fraction. Both procedures resulted in new ‘free’ volatiles. However, results varied depending on the type of treatment. This research is providing important insight into approaches for rapid estimation of ‘aroma potential’ of grapes.

Development of an Enology Outreach Program

There has been a chronic underinvestment in extension and outreach for the wine industry. The specific goal of this proposal is the development of a comprehensive program for extension and outreach in enology. This comprehensive program includes an interactive web site that will serve both researchers in enology and winery personnel. With the plethora of information sources currently available on the internet, searching effectively and efficiently for pertinent and accurate information has become challenging. This site will function as a means to link researchers across the United States and internationally that have an active program or interest in enology. The aim of the site is to share information within the research and production communities, facilitate collaboration, eliminate unnecessary redundancy, and foster communication on issues of regional, national or global importance. The site was renamed ‘EnologyAccess’ (http://enologyaccess.org/) and launched under this name with an inaugural webinar in August of 2008. In this past year we developed the interactive tools and social networking for the site (ea2) which will be launched in the next couple of months. We are actively migrating content to this site and providing links to extension specialist and researcher websites across the nation and the world. For this site to be more useful we will need to develop a stream of income that will support the site curation. This year we launched one of the signature programs of our new extension center, Wine Flavor 101. The first courses in this series were sold out and we received a response rate on the course questionnaire of over 70{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23}. The surveys provided a wealth of ideas and constructive criticism for the programs which will assure their continued success. As we develop solid income streams we will be able to hire content curators and add more and more content to the site and offer an expanded line of programs. Progress on meeting our goals is slow but steady.

Metabolic Basis of Differing Ethanol Yields in Saccharomyces

The goal of this study is the metabolomic analysis of ten commercial wine yeast strains that show differences in fermentation behavior and in final ethanol yield. Five of these strains tend to give lower and five higher ethanol yields during grape juice fermentation. Since non-sterile cold-settled juices were to be used to mimic wine production conditions, genetically marked strains of each commercial strain were generated. These strains were marked with a drug resistance gene that encodes resistance to kanamycin or G418. Initial experiments compared the fermentation performance of these strains to their parental strains and there were no differences noted. The kanamycin resistance gene was inserted into the HO gene which is required for yeast mating and not expressed in diploid cells thus it presents an attractive location at which to insert foreign marker DNA. The strains were grown in six replicate fermentations for the metabolomic analysis. Ethanol yields and dominance of the fermentation by the strains were monitored. One strain was not able to complete the fermentation of this juice but it was still taken for metabolomic analysis as this may reveal why it eventually arrested fermentation. Comparisons of the metabolomics data for high and low ethanol-producing strains suggests that low ethanol producers maintain active growth longer than high ethanol producers thus directing more sugar carbon towards biosynthetic intermediates and cellular components than high producers. High ethanol producing strains also showed evidence of the accumulation of degradation products of plant cell wall polysaccharides. This has not been observed before and offers the possibility that some of these components may be catabolized as well at this time which would boost yields of ethanol even further. Analysis of the metabolite pool levels of strains with intermediate ethanol production is currently underway.

Metabolic Profiling of Grape and Wine Aromas

The complex aroma of wine is derived from many sources, with grape-derived components being responsible for the varietal character. The ability to monitor grape aroma compounds would allow for better understanding of how vineyard practices and winemaking processes influence the final volatile composition of the wine. Previously we developed a procedure using GC-MS combined with solid-phase microextraction (SPME) for profiling the free volatile compounds in Cabernet Sauvignon grapes. During the current funding year we have modified this procedure in order to determine the volatile glycoside content of grapes using acid and enzyme hydrolysis conditions. The results indicate acid hydrolysis at low pH and high temperature can release from 50-80{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the total aglycone present in the sample. However, extensive degradation of many free volatile aglycones also occurs, with the effect being dependent on the compound studied and the hydrolysis conditions. This makes it difficult to use acid hydrolysis conditions to predict the ?potential? volatile composition of the grapes. This information is needed to understand the effects of viticultural practices on grape aroma composition and to be able to evaluate the effects of winemaking processes on changes in grape composition throughout the winemaking process. Further study is needed in order to minimize artifactual changes occurring from acid hydrolysis of volatile glycosides in grapes while maximizing their hydrolysis prior to analysis. As recently noted by Hayasaka et al. (2010), availability of rapid, sensitive profiling methods is important in assessing the nonvolatile fraction of grapes for a wide variety of industry applications.