Bruce W. Zoecklein

Production Wine Analysis

Section I-Sampling, Fermentation, and Production Analysis.- 1 / Fruit Quality and Soluble Solids.- 2 / Alcoholometry.- 3 / Extract.- 4 / Hydrogen Ion (pH) and Fixed Acids.- 5 / Volatile Acids.- 6 / Carbohydrates: Reducing Sugars.- 7 / Phenolic Compounds and Wine Color.- 8 / Oxygen, Carbon Dioxide, and Ascorbic Acid.- Section II-Microbial Stability.- 9 / Sulftir Dioxide.- 10 / Sulfur Containing Compounds.- 11 / Other Preservatives: Sorbic Acid, Benzoic Acid, and Dimethyldicarbonate.- 12 / Wine Microbiology.- Section III-Chemical Stability.- 13 / Tartaric Acid and its Salts.- 14 / Copper.- 15 / Iron and Phosphorus.- 16 / Nitrogenous Compounds.- Section IV-Remedial Actions.- 17 / Fining and Fining Agents.- 18 / Correction of Tartrate Instabilities.- 19 / Removal of Copper and Iron-The Hubach Analysis.- Appendixes.- Appendix I /Chromatographic Techniques.- Appendix II /Laboratory Reagent Preparation.- Appendix III /Laboratory Media and Stains.

Quantification of glycosidase activities in selected yeasts and lactic acid bacteria

Using a model system, the activities of α-L-arabinofuranosidase, β-glucosidase, and α-L-rhamonopyranosidase were determined in 32 strains of yeasts belonging to the genera Aureobasidium, Candida, Cryptococcus, Hanseniaspora, Hansenula, Kloeckera, Metschnikowia, Pichia, Saccharomyces, Torulaspora and Brettanomyces (10 strains); and seven strains of the bacterium Leuconostoc oenos. Only one Saccharomyces strain exhibited β-glucosidase activity, but several non-Saccharomyces yeast species showed activity of this enzyme. Aureobasidium pullulans hydrolyzed α-L-arabinofuranoside, β-glucoside, and α-L-rhamnopyranoside. Eight Brettanomyces strains had β-glucosidase activity. Location of enzyme activity was determined for those species with enzymatic activity. The majority of β-glucosidase activity was located in the whole cell fraction, with smaller amounts found in permeabilized cells and released into the growth medium. Aureobasidium pullulans hydrolyzed glycosides found in grapes.

Effect of fermentation, aging and thermal storage on total glycosides, phenol-free glycosides and volatile compounds of White Riesling (Vitis vinifera L.) wines

There is growing recognition of the significance of the products of glycoside hydrolysis to varietal wine aroma. White Riesling wines were produced from four strains of Saccharomyces cerevisiae. Wines underwent conventional aging or anaerobic thermal storage (20 days at 45°C) either 2 or 40 months post-fermentation to quantify influences on total glycosides, phenol-free glycosides and selected volatiles. Glycoside and free volatile concentrations were estimated by analysis of glycosyl-glucose and gas chromatography/mass spectrometry, respectively. Thermal storage of wines 2 months post-fermentation reduced the total glycosides by an average of 33% for all yeasts and increased the concentration of free benzyl alcohol while decreasing the concentration of free linalool and geraniol. Conventional aging for 40 months reduced the total and phenol-free glycosides equally among yeasts by an average of 60%, with phenol-free glycosides averaging 80% of the total. Thermal storage of aged wines reduced the total glycoside concentration by an additional 29%. The effect of thermal storage on selected volatile phenols, higher alcohols, esters, acids, terpenes, carbonyl compounds, C-13 norisoprenoids and six-carbon alcohols was variable depending upon the component.

Electronic Nose Evaluation of Cabernet Sauvignon Fruit Maturity

Abstract The ability of an electronic nose to classify cabernet sauvignon (Vitis vinifera L.) fruit based on maturity levels was investigated over two seasons. Maturity of samples collected 18, 19, and 20 weeks post-bloom was evaluated by measuring berry weight, pH, Brix, titratable acidity, total phenols, color intensity, hue, total anthocyanins, and total and phenol-free glycosides. Results were compared, using discriminant and canonical discriminant analysis, with analysis of headspace volatiles via a hand-held electronic nose. The electronic nose was able to determine differences among the three sample groups in both seasons. Additionally, in one season electronic nose measurements were compared to chemical analyses of samples collected from east and west sides of north – south oriented vineyard rows. Results demonstrated the ability of the electronic nose to distinguish fruit from vine canopy sides. Field measurements demonstrated the potential for the electronic nose as a rapid, non-destructive tool for evaluating grape maturity.

Phenolic Compounds and Wine Color

Variations in wine types and styles are largely due to the concentration and composition of wine phenols. From the vineyard to production and aging, fine wines can be viewed in terms of management of phenolic compounds. Phenols are responsible for red wine color, astringency, and bitterness; they contribute to the olfactory profile; serve as important oxygen reservoirs and as substrates for browning reactions.

Electronic Nose Analysis of Cabernet Sauvignon (Vitis vinifera L.) Grape and Wine Volatile Differences during Cold Soak and Postfermentation

Cold soak is a prefermentation maceration process at cold temperatures, traditionally used to enhance red wine color. This study monitored changes in Vitis vinifera L. cv. Cabernet Sauvignon volatiles using a commercial conducting polymer electronic nose (ENose) during a five-day cold soak and postfermentation. Principal component analysis (PCA) of juice volatiles detected by the ENose during cold soak showed PC1 accounted for 95.7% of the variation. Various volatile associations were made with specific ENose sensors. In comparison, PCA of must chemistries had 52.4% of the variation accounted for by PC1. The PCA of wine volatiles detected by GC-MS showed PC1 accounted for 97.1% of the variation between control and cold soak treatment, where control wine volatiles were associated with several ethyl esters, while cold soak wine volatiles were associated with diethyl succinate, isovaleric acid, benzyl alcohol, 3-methyl butanol, cis-3-hexenol, γ-nonalactone, benzaldehyde, 2-methyl propanol, phenethyl acetate, 1-octanol, β-damascenone, terpinene-4-ol, γ-butyrolactone, ethyl acetate, hexanoic acid, citronellol, phenethyl alcohol, and n-butanol. Comparatively, PC1 accounted for 100% of the total variance when using the ENose to measure volatile composition. Sensory evaluation did not demonstrate significant differences in aroma between control and cold soak wines. This study demonstrates differences in volatile chemistry between control and cold soak wines, as well as the ability to use a conducting polymer ENose as a simple tool for analysis of volatiles.

Prediction of Prefermentation Nutritional Status of Grape Juice

Five methods for evaluating nitrogen status were compared using 70 Cabernet Sauvignon juice samples: nitrogen by o -phthaldialdehyde (NOPA), arginine NOPA, enzymatic ammonia, Formol, and high-performance liquid chromatography (HPLC). Parallel recovery studies using model solutions of various amino acids and ammonia, presented singly and in combination, were also conducted. The results from two fruit-processing methods were compared using immature and mature berries. NOPA measurements were significantly higher in mature, pressed whole berry-derived samples, compared with homogenized juice. Adjustment of formaldehyde pH prior to analysis was found to be critical to consistency of the Formol method. Average amino acid recoveries for the Formol titration ranged from 82 to 99%. Average recovery for proline was 16.9 ± 0.4%. Ammonium nitrogen was also recovered (84 ± 3%) in the Formol procedure. Formol results trended significantly with NOPA. The correlation coefficient between Formol and NOPA plus NH4+ was 0.87, with Formol values being higher. The average deviation between the Formol and HPLC plus NH4+ and between the NOPA plus NH4+ and HPLC plus NH4+ was 7.3%. Acknowledgments The authors would like to thank the following agencies for their assistance in funding this research: Virginia Winegrowers Advisory Board, California Agricultural Technology Institute, California Competive Grants Program and the American Vineyard Foundation. Additional thank you to Sandy Brown, Robert Henry, Dan Musso, Jeremy Weintraub, Lawrence Herder, Steve Marko, and John Giannini.

Electronic Nose Evaluation of the Effects of Canopy Side on Cabernet franc (Vitis vinifera L.) Grape and Wine Volatiles

The effect of grapevine canopy side (north versus south and east versus west) on grape and wine volatiles of Cabernet franc was evaluated during two growing seasons using two electronic nose systems based on conducting polymers and surface acoustic waves. Data from three sampling dates per season from both electronic noses were compared with physicochemistry and wine aroma sensory evaluations. Univariate and multivariate statistical analyses generally indicated grape physicochemistry indices could not differentiate consistently (p > 0.05) between canopy sides across growing seasons and sampling dates. Both electronic nose (ENose) systems provided complete discrimination of canopy sides for grapes and wine using canonical discriminant analysis. On average, the surface acoustic wave-based ENose explained <50% of variation for grapes and <60% for wine using the first principal component, compared to >80% for the conducting polymer-based ENose. Wine aroma sensory evaluation differentiated canopy sides in three of four evaluations.

Monitoring Effects of Ethanol Spray on Cabernet franc and Merlot Grapes and Wine Volatiles Using Electronic Nose Systems

The ability of two electronic nose systems (conducting polymer and surface acoustic wave-based) to differentiate volatiles of grapes and wines treated with an aqueous ethanol spray (5% v/v) at veraison was evaluated. Ethanol spray induced fruit ethylene production immediately posttreatment, which then declined progressively. The electronic nose evaluations of grape volatiles were compared with Cabernet franc and Merlot physicochemistry and with wine gas chromatographic and aroma sensory data. Canonical discriminant and principal component analysis found that both electronic nose systems and the physicochemical measures (Brix, TA, pH, color intensity and hue, total phenols, glycosides, and berry weight) were able to discriminate between ethanol-treated and untreated grapes and wines for both cultivars. Grape physicochemical treatment differences were due mainly to variations in hue, phenolic-free glycosides, and total phenols. Aroma sensory evaluations using a consumer panel differentiated between ethanol treatments and controls for Merlot, but not for Cabernet franc wines.

Discrimination of wines produced from Cabernet Sauvignon grapes treated with aqueous ethanol post-bloom using an electronic nose

Wine discrimination and analysis is typically done through chemical analysis and sensory evaluation by a trained panel. Both of these methods are proven to be successful in wine discrimination, but require extensive preparation, time and money. The electronic nose is an objective, rapid-analysis tool that has been used in the food industry for a number of applications. The purpose of this study was to determine if an electronic nose can accurately discriminate between Cabernet Sauvignon (Vitis vinifera L.) wines made from grapes that have received different pre-harvest but post-bloom spray treatments to enhance growth.Aqueous ethanol, which has been shown to impact fruit maturity, was sprayed on the grape clusters at 13 weeks post bloom in different concentrations (control, 5% and 10% v/v). Chemical analysis was able to accurately discriminate between the wines produced from these grapes. Triangle difference testing by a consumer panel was not able to differentiate between the different treatments. The electronic nose data was able to accurately identify the control group and the 5% EtOH treatment 90% of the time. Placement of the 10% EtOH group was only 13% correct. The results show the promising potential for an electronic nose to discriminate between control and treated wine samples.