Kenneth C. Fugelsang

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.

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.

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%.nnAcknowledgments 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.

Yeasts and Molds

Despite the increasing availability of modern classification techniques based on similarities at the gene level, routine laboratory identification of yeasts still relies on microscopic comparison of the isolate’s cell shape, how it reproduces (asexually versus sexual), as well as utilization of various carbon and nitrogen compounds, and metabolites produced.

Iron and Phosphorus

Yeasts require trace levels of various mineral compounds including iron. At low concentrations, iron plays an important role in metabolism as an enzyme activator, stabilizer, and functional component of proteins. At higher-than-trace levels, iron has other roles: altering redox systems of the wine in favor of oxidation, affecting sensory characteristics, and participating in the formation of complexes with tannins and phosphates resulting in instabilities. This complex formation, also termed “casse,” is seen initially as a milky white cloud and later as a precipitate. Two iron-containing casses may form in wines: “white” (ferric phosphate) and “blue” (ferric tannate casse). The former represents the most commonly encountered iron-related casse.

Fermentation and Post-fermentation Processing

Fermentation is one of the oldest methods of food preservation. The hygenic value of wine, as an alternative to local water supplies, has been known since well before the crusades. Although the interactive effects of ethanol, low pH, and the presence of preservatives have generally been credited for the antimicrobial properties of wine, recent research has clearly shown that health and hygenic benefits go well beyond these to include other naturally occurring compounds as well (Weisse et al., 1995; Muller and Fugelsang, 1996).

Practical methods of measuring grape quality

Abstract: Grape quality depends to a large extent on various metabolites, timing and completeness of ripening and the ripening synchrony of skins, seeds, stems, and pulp. This chapter outlines grape quality issues of importance in stylistic winemaking.

The Lactic Acid Bacteria

The lactic acid bacteria (LAB) isolated from wine are located in two families and three genera (with several species and strains). The Lactobacillaceae, represented by the genus Lactobacillus, includes rod-shaped Gram-positive species and their respective strains (see Fig. 1-1), whereas the Streptococcaceae represented by the genera Pediococcus and Leuconostoc, includes Gram-positive coccoid- or coccobacilloid-shaped isolates (see Figs. 1-2 and 1-3). Both groups may grow as somewhat characteristic aggregations of cells. These may include chains of lenticular or sausage-shaped cells, in the case of Leuconostoc oenos, filamentous chains (Lactobacillus fructivorans), and tetrads that result from division in two planes (Pediococcus damnosus).

Fining and Fining Agents

Fining is the addition of a reactive or adsorptive substance to remove or reduce the concentration of one or more undesirable constituents. Fining agents are added to juices, wines, and sparkling wine cuvees for the purposes of enhancing clarity, color, aroma, flavor, and/or stability modification. Fining agents can be grouped according to their general nature.