Maurizio Ugliano

Assimilable nitrogen utilisation and production of volatile and non-volatile compounds in chemically defined medium by Saccharomyces cerevisiae wine yeasts

Surveys conducted worldwide have shown that a significant proportion of grape musts are suboptimal for yeast nutrients, especially assimilable nitrogen. Nitrogen deficiencies are linked to slow and stuck fermentations and sulphidic off-flavour formation. Nitrogen supplementation of grape musts has become common practice; however, almost no information is available on the effects of nitrogen supplementation on wine flavour. In this study, the effect of ammonium supplementation of a synthetic medium over a wide range of nitrogen values on the production of volatile and non-volatile compounds by two high-nitrogen-demand wine fermentation strains of Saccharomyces cerevisiae was determined. To facilitate this investigation, a simplified chemically defined medium that resembles the nutrient composition of grape juice was used. Analysis of variance revealed that ammonium supplementation had significant effects on the concentration of residual sugar, L-malic acid, acetic acid and glycerol but not the ethanol concentration. While choice of yeast strain significantly affected half of the aroma compounds measured, nitrogen concentrations affected 23 compounds, including medium-chain alcohols and fatty acids and their esters. Principal component analysis showed that branched-chain fatty acids and their esters were associated with low nitrogen concentrations, whereas medium-chain fatty esters and acetic acid were associated with high nitrogen concentrations.

Evolution of 3-mercaptohexanol, hydrogen sulfide, and methyl mercaptan during bottle storage of Sauvignon blanc wines. Effect of glutathione, copper, oxygen exposure, and closure-derived oxygen.

The effects of wine composition and postbottling oxygen exposure on 3-mercaptohexanol (3-MH), hydrogen sulfide (H2S), and methyl mercaptan (MeSH) were investigated. A Sauvignon blanc wine with initial copper concentration of 0.1 mg/L was treated with copper sulfate and/or glutathione (GSH) prior to bottling to give final concentrations of 0.3 and 20 mg/L, respectively. The wines were bottled with a synthetic closure previously stored in either ambient air or nitrogen to study the effect of the oxygen normally present in the closure. Bottled wines were stored for 6 months in either air or nitrogen to study the effect of oxygen ingress through the closure. Copper addition resulted in a rapid initial decrease in 3-MH. During storage, a further decrease of 3-MH was observed, which was lower with GSH addition and lowered oxygen exposure. H2S accumulated largely during the second 3 months of bottle storage, with the highest concentrations attained in the wines treated with GSH and copper. Lower oxygen from and through the closure promoted H2S accumulation. The concentration of MeSH was virtually not affected by the experimental variables at 6 months, although differences were observed after 3 months of storage. The implications for wine quality are discussed.

Comparison of inorganic and organic nitrogen supplementation of grape juice – Effect on volatile composition and aroma profile of a Chardonnay wine fermented with Saccharomyces cerevisiae yeast

Inorganic nitrogen salts, and to a growing extent organic nitrogen preparations, are widely used to ameliorate a nitrogen deficiency in wine fermentation, but the impact of nitrogen supplementation on perceived wine sensory profile is essentially unknown. Supplementation of a low nitrogen Chardonnay grape juice with either ammonium nitrogen or combined amino acid and ammonium nitrogen showed that the type of nitrogen and concentration in the range 160-480mgN/l had a substantial impact on the formation of yeast volatile compounds and perceived wine aroma. Addition of amino acid and ammonium nitrogen increased both acetate and medium chain fatty acid esters to a greater extent and decreased higher alcohols to a lesser extent than ammonium nitrogen alone whereas ammonium nitrogen substantially increased ethyl acetate and acetic acid. Low nitrogen wines were rated relatively low in floral/fruity aroma descriptors, while moderate nitrogen wines showed a good balance between desirable and less desirable attributes, whereas high nitrogen produced either an acetic/solvent character or highest ratings for floral/fruity attributes, depending on nitrogen type. These results show that amount and type of nitrogen supplement can substantially modulate Chardonnay wine volatiles composition and perceived aroma.

Oxygen contribution to wine aroma evolution during bottle aging.

Wine aroma undergoes major changes during bottle aging, which are deeply influenced by the degree of oxygen exposure in the bottle. This review discusses the involvement of oxygen in the main chemical transformations occurring in wine aroma composition during bottle aging, with particular emphasis on the formation of oxidative aroma compounds and formation/degradation of sulfur-containing volatile compounds. The implications for wine sensory properties are discussed, as well as some practical aspects of oxygen management during bottle aging, including the role of closure oxygen permeability.

Effect of nitrogen supplementation and saccharomyces species on hydrogen sulfide and other volatile sulfur compounds in Shiraz fermentation and wine

A Shiraz must with low yeast assimilable nitrogen (YAN) was supplemented with two increasing concentrations of diammonium phosphate (DAP) and fermented with one Saccharomyces cerevisiae and one Saccharomyces bayanus strain, with maceration on grape skins. Hydrogen sulfide (H(2)S) was monitored throughout fermentation, and a total of 16 volatile sulfur compounds (VSCs) were quantified in the finished wines. For the S. cerevisiae yeast strain, addition of DAP to a final YAN of 250 or 400 mg/L resulted in an increased formation of H(2)S compared to nonsupplemented fermentations (100 mg/L YAN). For this yeast, DAP-supplemented fermentations also showed prolonged formation of H(2)S into the later stage of fermentation, which was associated with increased H(2)S in the final wines. The S. bayanus strain showed a different H(2)S production profile, in which production was inversely correlated to initial YAN. No correlation was found between total H(2)S produced by either yeast during fermentation and H(2)S concentration in the final wines. For both yeasts, DAP supplementation yielded higher concentrations of organic VSCs in the finished wines, including sulfides, disulfides, mercaptans, and mercaptoesters. PCA analysis indicated that nitrogen supplementation before fermentation determined a much clearer distinction between the VSC profiles of the two yeasts compared to nonsupplemented fermentations. These results raise questions concerning the widespread use of DAP in the management of low YAN fermentations with respect to the formation of reductive characters in wine.

Free and hydrolytically released volatile compounds of Vitis vinifera L. cv. Fiano grapes as odour-active constituents of Fiano wine.

Grape-derived volatile compounds, including those released from odourless glycosidic precursor present in the grape, are strongly associated with the varietal aroma characteristic of non-aromatic wines. In this study, free and glycosidically bound volatile compounds of Fiano grapes have been identified and quantified by means of gas chromatography-mass spectrometry (GC-MS). The free volatile fraction of Fiano grapes was mainly characterised by the occurrence of several aliphatic alcohols, with minor amounts of the monoterpenes linalool and geraniol, and traces of the norisoprenoid beta-damascenone. The volatile fraction obtained from either enzymatic or acid hydrolysis of juice glycosides was more complex, and contained compounds belonging to the chemical classes of terpenes, norisoprenoids, benzenoids, and aliphatic alcohols. Linalool, geraniol, teprinen-4-ol, 1,1,6-trimethyl-1,2-dihydronaphtalene (TDN), beta-damascenone, (E)-1-(2,3,6-trimenthylphenyl)buta-1,3-diene (TPB), ethyl cinnamate, and 4-vinyl guaiacol were detected by GC-olfactometry (GC-O) as odorants of young Fiano wine that were formed through hydrolysis of grape precursors. Pathways of formation of these compounds during winemaking were investigated. Yeast-driven enzymatic hydrolysis of glycosides was the major route for linalool and geraniol formation, while acid hydrolysis led to the formation of terpinen-4-ol, TDN, beta-damascenone, TPB, and ethyl cinnamate.

Oxygen consumption and development of volatile sulfur compounds during bottle aging of two Shiraz wines. Influence of pre- and postbottling controlled oxygen exposure.

The evolution of different volatile sulfur compounds (VSCs) during bottle maturation of two Shiraz wines submitted to controlled oxygen exposure prior to bottling (through micro-oxygenation, MOX) and postbottling (through the closure) was investigated. H(2)S, methyl mercaptan (MeSH), and dimethyl sulfide (DMS) were found to increase during aging. Lower postbottling oxygen exposure, as obtained by different degrees of oxygen ingress through the closure, resulted in increased H(2)S and methyl mercaptan. In one wine MOX increased the concentration of H(2)S and methyl mercaptan during maturation. Dimethyl disulfide and DMS were not affected by any form of oxygen exposure. Overall, postbottling oxygen had a stronger influence than MOX on the evolution of VSCs. Data suggest that dimethyl disulfide was not a precursor to methyl mercaptan during bottle maturation. For the two wines studied, a consumption of oxygen of 5 mg/L over 12 months was the most effective oxygen exposure regimen to decrease accumulation of MeSH and H(2)S during bottle aging.

Volatile and Color Composition of Young and Model-Aged Shiraz Wines As Affected by Diammonium Phosphate Supplementation Before Alcoholic Fermentation

A Shiraz must with low yeast assimilable nitrogen (YAN) was supplemented with two concentrations of diammonium phosphate (DAP) and then fermented with maceration on grape skins. The nonvolatile, volatile, and color composition of the final wines were investigated. Ethanol and residual sugars were not affected by DAP supplementation, while glycerol, SO 2, and residual YAN increased and acetic acid decreased. DAP-supplemented treatments gave rise to higher concentrations of acetates, fatty acids, and fatty acid ethyl esters but lower concentrations of branched-chain fatty acids and their ethyl esters. No major difference between treatments was observed for higher alcohols, monoterpenes, norisoprenoids, and low-molecular-weight sulfur compounds. DAP-supplemented fermentations resulted in wines with higher concentrations of malvidin-3-glucoside, higher color intensity, and altered color tonality. Model aging studies indicated that higher concentrations of esters are still present in wines from the DAP-treated fermentations after aging. DAP supplementation also resulted in increased concentrations of dimethyl sulfide after model aging. It can be concluded that DAP treatment of a low YAN must fermented by maceration on skins can significantly affect wine color, aroma, and flavor.

Evolution of Phenolic Compounds and Astringency during Aging of Red Wine: Effect of Oxygen Exposure before and after Bottling

The aim of this study was to evaluate the effect of oxygen exposure of red wine, before (micro-oxygenation) and after (nano-oxygenation) bottling, on the phenolic composition and astringency of wine. The astringency was evaluated by sensory analysis and by a method based on the SDS-PAGE of salivary proteins after reaction of saliva with wine (SPI, saliva precipitation index). Micro-oxygenation caused a stabilization of color, but this effect disappeared after long aging. For the wine with the lower pH a decrease of wine astringency and SPI was observed 42 months after micro-oxygenation. Oxygen ingress through the closure postbottling was positively correlated with the decrease of SPI. Therefore, the astringency and reactivity of wines toward salivary proteins of a bottled red wine can be modulated by controlled oxygen exposure during aging. For both experiments the effect of oxygen exposure depended on wine composition.

Impact of Headspace Oxygen and Closure on Sulfur Dioxide, Color, and Hydrogen Sulfide Levels in a Riesling Wine

Following an experimental design replicating typical winery conditions, a Riesling wine was bottled with different headspace oxygen levels and sealed with either a coextruded closure or a screwcap to investigate the impact of headspace oxygen and closure oxygen transfer rate on wine evolution. Using luminescence technology, dissolved oxygen and headspace oxygen, as well as oxygen ingress through the closure, were monitored during 24 months of bottle storage. Under typical winery conditions, headspace oxygen introduced at bottling was found to be a major component of oxygen in bottled wine. Headspace oxygen at bottling influenced loss of sulfur dioxide during bottle storage, being the main cause of sulfur dioxide decline during the first four months after bottling in 375 mL bottles. The loss of sulfur dioxide was not correlated with the evolution of dissolved oxygen, but with the total amount of oxygen consumed by the wine. After 24 months in the bottle, color differences due to different headspace oxygen and closure oxygen transfer rate were generally minor. Conversely, differences in closure oxygen transfer rate were responsible for significant differences in the final concentration of the off-odor compound hydrogen sulfide, with screwcap generally associated with higher levels of this compound. Even if less significantly, the amount of oxygen present in the headspace at bottling also had an effect on final hydrogen sulfide, with higher concentrations observed in wines bottled with lower headspace oxygen.