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%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.

Effect of wine closure oxygen permeability on volatile sulfur compounds in Pinot noir and Chardonnay wines during post-bottle aging

It is generally assumed that bottled wine is a dynamic system. A proper wine bottle closure will allow a dynamic and healthy gas exchange between the wine the air. The amount of oxygen ingression through the wine closure can directly affect wine aging and flavor development. Too much oxygen ingress can oxidize the wine during post-bottle aging, whereas too little oxygen ingress may slow flavor development. It is a concern that screw caps with too low oxygen permeability may even induce ?reduced? sulfur off-flavor due to accumulation of volatile thiols. To test this hypothesis, natural cork (up and down), synthetic, and screw caps with Saran-Tin, Saranex and low density polyethylene (LDPE) lines with various oxygen permeability were investigated on both Pinot noir and Chardonnay wines over two years storage. For Chardonnay wine, the LDPE screw cap gave the highest dissolved oxygen, lowest free SO2, and highest absorbance at 420 nm. The Saran-Tin screw cap gave the lowest dissolved oxygen. Similar trends were observed for Pinot noir wines, with Saran-Tin screw cap gave the lowest dissolved O2 and highest free SO2 and total SO2. Decreasing trend was observed for some sulfur compounds during 2 years of storage. Methanethiol had the highest decrease in wines with LDPE screw cap and synthetic closures, correlated with high oxygen permeability of these closures and low SO2 content in the wines. Similar pattern was observed for H2S. On the other hand, a decreasing trend was observed for ethylthiol acetate due to hydrolysis, and was not affected by closure types. Other sulfur compounds remained stable or decreased slightly, and there was no elevated sulfur compound for any screw cap closures after two years of storage. In addition, we did not detect any significant amount of dimethyl disulfide and dimethyl trisulfide in any of the experimental wines. Expert sensory panel did not pick up sulfur off-flavor in the experimental wines, and trained sensory panelist did not pick up any aroma difference between the Saran-Tin and LDPE screw capped wines. These results suggest the original wine status was probably more important, and the data does not support the hypothesis that dimethyl disulfide could converted to methanethiol under low oxygen conditions.

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 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 “Enology Access” and launched under this name with an inaugural webinar in August of 2008. This current year focused on analysis of site software packages with the goal of making sure that the interactive types of programming that we are planning could be supported by the software. Joomla was found to have the best capabilities including being able to interact with other types of programming. Videos, text content and an interactive comprehensive glossary have been uploaded to the site. Other materials are under development and will be uploaded soon. Researchers and institutions are being invited to register on the site and many have already done so. Webinars and live seminar broadcasting has been successfully implemented via the Adobe Connect software maintained on campus. Thus the site has been successfully launched and content is continuing to be developed. In the next year we will develop more interactive educational capabilities.

Oxidation of Wine: Control for Quality

Very good progress has been made in understanding the Fenton reaction. Data collected in Denmark in collaboration with Skibsted revealed the identity of major free radical in wine, demonstrating that the Fenton reaction is important and the role of sulfite in slowing this reaction. Studies of additives to prevent oxidation are currently underway. This research has stimulated many other efforts in wine oxidation around the globe.

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 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. In the current funding year an Implementation and Advisory
Committee for the Enology Extension Online web site was formed. The committee
consists of: Dr. James Harbertson (Washington State University), Dr. James Osborne
(Oregon State University), Dr. Brent Trela (Texas Tech University), Dr. Trevor Phister
(North Carolina State University) and Dr. Bruce Zoecklein (Virginia Tech). Dr. Bisson is
chairing the group and the committee is assisted by Kay Bogart. The Implementation and
Advisory Committee has designed the scope of the site, which is described in detail in the
request for continuing funding. In addition the group considered the best mechanisms for
creation and maintenance of the site. The site has been named ?Enology Extension
Online? and will be launched in April 2008.

A determination of the role of fruit maturity in the sensory properties of

This project attempts to clarify the consequences for wine flavor that result from harvesting fruit at different maturities. It aims to do a complete study (from a sensory and chemical analyses point of view) from the vineyard to the resultant wines. During the current funding period we did the descriptive sensory analysis of the 2006 wines, did chemical analyses of the 2006 wines and had a winemaker panel evaluate the quality of a subset of the 2006 wines. We harvested the 2007 grapes from a single vineyard at six time-points over a fourteen week period (August 23 to November 28, 2007). The samples spanned maturity levels from what would be considered early/normal harvest (average Brix=21) to late harvest (average Brix=30.8). The fresh grapes were evaluated by a trained descriptive sensory panel and by Napa Valley winemakers. The trained panel found subtle but consistent differences among grapes harvested at different times and these results were very similar to those found in 2006. Specifically, lower Brix grapes were more sour in skin and pulp, had more vegetative skins and had greener, more bitter seeds, whereas higher Brix grapes were sweeter, more fruity, more squishy with browner and nuttier seeds and more raisin-flavored skins. The Napa winemakers each used their own method to determine whether the sample grapes were ready to be harvested and in 2006 as well as 2007 they all agreed that grapes from harvest 1 through 3 were not ready to be picked. However, for harvests 4 through 6 there were some differing clusters of winemakers. Additionally, grape berry samples were prepared and frozen for chemical analyses. There were differences between the 2006 and 2007 grapes in the concentration of tannins, anthocyanins and 2-methoxy-3isobutyl pyrazine concentrations. The 2007 wines were made and will be evaluated by a trained sensory descriptive panel (in April) and Napa Valley winemakers (in June). The descriptive analysis of the 2006 wines showed that wines made from grapes with higher initial sugar content were higher in dark fruit, dry fruit and spicy flavors and lower in sourness as well as lower in fresh and cooked vegetative flavors. Additionally, for higher initial sugar concentration musts adding water prior to fermentation had a larger effect on the wine sensory attributes than adding water after fermentation. The winemakers thought that wines made with grapes harvested between 24.7 and 26 Brix were of better quality, and would receive the highest retail price. Wine chemical analyses of 2006 and 2007 wines are on-going.

Characterization of ethyl phenols and other volatile components in Brettanomyces bruxellensis off-flavor occurrence

Brettanomyces bruxellensis contributes flavors to wine which are described as Band-aid,
burnt plastic, smoky, spicy, leathery, horse sweat, and barnyard. While winemakers
debate whether the ‘Brett’ aroma should always be considered an off-flavor, there is a
consensus reflected in the AVF funding priorities that an improved understanding of
Brettanomyces will assist the winemaking community. Building on previous work
performed at Cornell, we had proposed several microbiological and chemical studies for
the 2007-08 research cycles. Specifically, our objectives were to investigate B.
bruxellensis volatile phenol production in relation to the precursor concentration and to
the yeast growth phase. Five strains of B. bruxellensis strain were studied in model wine
with variable levels of hydroxycinnamic acid (HCA) precursors. For all strains, we
observed similar growth kinetics for concentrations up to 5 mg/L of the HCA precursors.
At 10 mg/L of HCA precursors, yeast growth was slowed during the exponential phase,
but the final yeast concentration was unchanged. Volatile phenol production was highly
correlated to HCA level for all initial precursor concentrations. The conversion
efficiency of HCA precursors (1-10 mg/L) to volatile phenols was greater than 50% in
most cases, with the exception of 4-EP production by B. bruxellensis strain 2091 (<30%).
4-EP production was more differentiated among strains and started slightly later than 4-
EG. In summary, this work has demonstrated that early detection of most strains of B.
bruxellensis before the midpoint of the exponential growth phase can allow for
intervention prior to production of volatile phenols, that at least one strain is capable of
producing detectable levels of phenols much earlier in growth, and that potential volatile
phenol production is well predicted by precursor concentration.

Oxidation of wine, Control for Quality

There was extensive progress towards unraveling the key reactions in the oxidation of ethanol with hydrogen peroxide. Iron and its oxidation state are proving to be critical to the reaction. Paradoxically, the addition of oxygen to a simple Fenton reaction nearly stops the oxidation of ethanol. When sulfites are present, phenolics seem to enhance the oxidation, also unexpected because phenolics act as antioxidants on their own. The new understanding of oxidation revealed here is beginning to suggest means to better control oxidation and the next few months of this project should give some more direct guidance.

Evaluation of a Quality Control Tool for Predicting the Distribution of 2,4,6 -Trichloroanisole (TCA) in Cork Populations and Bottled Wines

2,4,6-trichloroanisole (TCA) transferred from natural cork closures to bottled wine was studied. The corks used in the study were all imported into California from Portugal. Ten different bales, provided by seven different cork suppliers, previously studied for their Releasable TCA (RTCA) in part one of same study, were used on a commercial bottling line with a California Chardonnay. After nine months of storage under normal commercial conditions, 100 bottles from each of the ten cork bales were opened and wine from each bottle analyzed for TCA. Results were presented in part two of same study. After twenty months, 60 bottles from each of the ten cork bales were opened and wine from each bottle analyzed for TCA. For each cork bale, the occurrence of bottles

A Determination of the Role of Fruit Maturity in the Sensory Properties of Paso Robles Cabernet Suavignon Wines

This project attempts to clarify the consequences for wine flavor that result from harvesting fruit at different maturities. It aims to do a complete study (from a sensory and chemical analyses point of view) from the vineyard to the resultant wines. During the 2006 harvest we harvested from a single vineyard at six time-points over a ten week period (September-November 2006). The samples spanned maturity levels from what would be considered early/normal harvest (average Brix=22) to late harvest (average Brix=30). The grapes were evaluated by a trained descriptive sensory panel and by Napa Valley winemakers. The trained panel found subtle but consistent differences among grapes harvested at different times. The Napa winemakers each used their own method to determine whether the sample grapes were ready to be harvested and that over the period of observation the grapes became more likely to be ready to pick. Additionally, grape berry samples were prepared and frozen for chemical analyses. The wines were made and will be evaluated by a trained sensory descriptive panel (in April) and Napa Valley winemakers (in June). Wine chemical analyses are on-going.