James P. Osborne

Degradation of free and sulfur-dioxide-bound acetaldehyde by malolactic lactic acid bacteria in white wine.

Aims:  Acetaldehyde is the major carbonyl compound formed during winemaking and has implications for sensory and colour qualities of wines as well as for the use of the wine preservative SO2. The current work investigated the degradation of acetaldehyde and SO2‐bound acetaldehyde by two commercial Oenococcus oeni starters in white wine.

Bacteria Important during Winemaking

Publisher Summary This chapter discusses the bacteria that are important during winemaking. Numerous bacterial species are present during the vinification process. The extent to which these species grow determines the types and concentrations of many substances that contribute to the aroma and flavor of a wine. Growth of bacterial species, such as Acetobacter / Gluconobacter , Lactobacillus , and Pediococcus , may cause spoilage of a wine through the production of off-flavors and aromas. Certain bacterial strains produce substances in wine such as biogenic amines and ethyl carbamate precursors that are of public health concern. Many interactions occur between different bacterial species and with the wine yeast Saccharomyce s. These interactions may be beneficial or detrimental to wine quality depending on the species involved. The chapter discusses the impact of the microorganisms on wine quality, public health concerns, and the interactions that occur between these microorganisms and Saccharomyces cerevisiae . Future research should include investigating the contribution of malolactic bacteria to wine flavor, the impact of Pediococcus species on the sensory qualities of wine, and the mechanisms involved in the inhibition of Saccharomyces by Lactobacillus species and the inhibition of malolactic fermentation by wine yeast.

Impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria

Aims:  To investigate the impact of acetaldehyde‐ and pyruvic acid‐bound sulphur dioxide on wine lactic acid bacteria (LAB).

Impact of Malolactic Fermentation on the Color and Color Stability of Pinot noir and Merlot Wine

Malolactic fermentation (MLF) is an integral step in red winemaking that results in a decrease in acidity and can also influence additional wine quality parameters. This study examined the impact of MLF on red wine color and the ability of Oenococcus oeni to degrade compounds important to the development of polymeric pigments. Pinot noir and Merlot wines were produced where a portion of the wines underwent a simultaneous alcoholic and malolactic fermentations with O. oeni strain VFO. Post-alcoholic MLFs were conducted using VFO and two additional O. oeni strains in sterile filtered wines. A control wine that did not undergo MLF was pH adjusted to the same pH as wines that had undergone MLF. Wines that underwent MLF (MLF+) contained lower concentrations of acetaldehyde and pyruvic acid than wines that did not undergo MLF (MLF-). Wines that underwent MLF with O. oeni VFO also had higher concentrations of caffeic and trans-p-coumaric acids. MLF+ wines had significantly lower color and polymeric pigment content than MLF-wines and contained significantly higher monomeric anthocyanins. Vitisin B concentrations were also significantly lower in wines that underwent MLF. These differences remained throughout nine months of storage, demonstrating that MLF can affect red wine color independent of pH change. While O. oeni influenced the concentration of phenolic and nonphenolic compounds involved in red wine color development there were no strain specific differences in color and polymeric pigment content.

Metabolism of Nonesterified and Esterified Hydroxycinnamic Acids in Red Wines by Brettanomyces bruxellensis

While Brettanomyces can metabolize nonesterified hydroxycinnamic acids found in grape musts/wines (caffeic, p-coumaric, and ferulic acids), it was not known whether this yeast could utilize the corresponding tartaric acid esters (caftaric, p-coutaric, and fertaric acids, respectively). Red wines from Washington and Oregon were inoculated with B. bruxellensis, while hydroxycinnamic acids were monitored by HPLC. Besides consuming p-coumaric and ferulic acids, strains I1a, B1b, and E1 isolated from Washington wines metabolized 40-50% of caffeic acid, a finding in contrast to strains obtained from California wines. Higher molar recoveries of 4-ethylphenol and 4-ethylguaiacol synthesized from p-coumaric and ferulic acids, respectively, were observed in Washington Cabernet Sauvignon and Syrah but not Merlot. This finding suggested that Brettanomyces either (a) utilized vinylphenols formed during processing of some wines or (b) metabolized other unidentified phenolic precursors. None of the strains of Brettanomyces studied metabolized caftaric or p-coutaric acids present in wines from Washington or Oregon.

Impact of Oenococcus oeni on Wine Hydroxycinnamic Acids and Volatile Phenol Production by Brettanomyces bruxellensis

The ability of commercial strains of Oenococcus oeni to degrade tartaric acid ester-bound hydroxycinnamic acids (TAE-HCAs) and their impact on the production of volatile phenols by Brettanomyces bruxellensis was investigated. Of 10 commercial O. oeni strains evaluated, only one strain, O. oeni Viniflora Oenos (VFO), was able to degrade TAE-HCAs during growth in a Pinot noir wine. This degradation resulted in an increase in the corresponding free forms of the hydroxycinnamic acids in the wine. As a result, growth of B. bruxellensis UCD-2049 in Pinot noir wine where malolactic fermentation (MLF) was conducted by VFO resulted in higher concentrations of 4-ethylphenol and 4-ethylguaiacol in this wine than in wine that did not undergo MLF or underwent MLF with O. oeni strains that did not degrade TAE-HCAs. While wineries must continue to use sound winemaking practices to prevent the growth of Brettanomyces spp. in their wines, minimizing the amount of free hydroxycinnamic acids in the wine will reduce the production of volatile phenols if growth of Brettanomyces spp. does occur. The use of an O. oeni strain that cannot degrade TAE-HCAs is a simple and practical strategy to help achieve this.

Production of SO2 Binding Compounds and SO2 by Saccharomyces during Alcoholic Fermentation and the Impact on Malolactic Fermentation

The objective of this study was to investigate the production of SO2 and SO2 binding compounds by wine yeast and the impact of the production of these compounds on the MLF at various time points during alcoholic fermentation. Fermentations were observed for a number of commercial wine yeasts in a synthetic grape juice and Pinot gris juice and SO2, acetaldehyde, pyruvic acid and α-ketoglutarate. Measurements were taken at multiple time points during the fermentation. Samples were taken from the fermentations at weekly intervals, sterile filtered, and inoculated with O. oeni strain VFO to induce MLF. Significant differences between the amount of SO2, acetaldehyde and pyruvic acid produced by the various yeast strains were noted. Some yeast strains such as FX10, CK S102, F15 and M69, produced significantly higher SO2 concentrations than other yeast strains and MLF was inhibited in these wines. Insignificant free SO2 was measured, indicating that bound SO2 rather than free SO2 was responsible for inhibition. At almost all time points of the alcoholic fermentation, acetaldehyde bound SO2 was determined to be the dominant species of bound SO2 present, suggesting that MLF inhibition by bound SO2 was due to acetaldehyde bound SO2.

Investigating High Hydrostatic Pressure Processing as a Tool for Studying Yeast during Red Winemaking

The application of high hydrostatic pressure (HHP) to inactivate microorganisms in a grape must (crushed grapes), coupled with autoclavable microscale fermentors, was investigated as a potential tool for studying the impact of yeast on red wine aroma and flavor. A Pinot noir grape must was inoculated with Saccharomyces cerevisiae, Brettanomyces bruxellensis, Kluveromyces thermotolerans, Lactobacillus hilgardii, Oenococcus oeni, and Acetobacter aceti at ~1 × 105 cfu/mL and subjected to HHP treatment for 10 min at 551 MPa (5510 bar). After HHP treatment no viable cells were detected in the grape must. Autoclavable microscale fermentors were then used to conduct replicate fermentations of HHP-treated and untreated Pinot noir grapes producing sufficient wine for chemical and sensory analysis. No differences were observed in fermentation rate between treatments, and variability between replicates was very low. No significant differences in color or hue were observed, but wine produced from HHP-treated grapes contained higher total phenolics. Sensory analysis of the wines by a trained panel revealed that other than a slight increase in overall fruit aroma there were no significant differences between any aroma and flavor descriptors. Results suggest that HHP processing of grapes, in conjunction with autoclavable microscale fermentors, could be used to conduct experimental red wine fermentations without the influence of native yeast and bacteria present on grapes and fermentation equipment.

Loss of Pinot noir Wine Color and Polymeric Pigment after Malolactic Fermentation and Potential Causes

Loss of Pinot noir wine color and polymeric pigment due to malolactic fermentation (MLF) and potential causes for these losses were studied. Delaying MLF was investigated as a method to minimize loss of color and polymeric pigment. Pinot noir wines were held at 13°C for 0, 14, 28, 100, and 200 days before inoculation with Oenococcus oeni strain Viniflora Oenos to induce MLF. Delaying MLF did not affect loss of color, but delaying MLF for increasing times reduced the loss of polymeric pigment and after 200 days no losses compared to the control were noted. The role of acetaldehyde and/or pyruvic acid degradation by O. oeni during MLF was investigated as a cause for reduced polymeric pigment formation. Wines that had undergone MLF were supplemented with acetaldehyde and/or pyruvic acid to the levels measured in control wines that did not undergo MLF. Wines made with added acetaldehyde had more color and polymeric pigment than MLF wines with no additions, and those made with added pyruvic acid had no change in color or concentration of polymeric pigment. However, addition of acetaldehyde did not completely prevent loss of color after MLF, and color loss due to fining by O. oeni was explored. Wines that did not undergo MLF that were exposed to inactivated O. oeni cells showed no difference in color, polymeric pigment concentration, or monomeric anthocyanin concentration compared to the control wines, suggesting that loss of color during MLF was not due to fining by O. oeni cells.

Influence of Winemaking Processing Steps on the Amounts of (E)-2-Decenal and Tridecane as Off-Odorants Caused by Brown Marmorated Stink Bug (Halyomorpha halys)

Brown marmorated stink bugs (BMSB) release stress compounds, tridecane and (E)-2-decenal, that affect final wine quality. This study focuses on determining the effect of wine processing on (E)-2-decenal and tridecane release in both red and white wines. Wines were produced by adding live BMSB to grape clusters at densities of 0, 0.3, 1, and 3 bugs/cluster. Compound concentrations were measured using headspace solid phase microextraction with multidimensional gas chromatography and mass spectrometry. For red wines, the highest levels of stress compounds were found using 3 BMSB/cluster [tridecane, 614 μg/L; (E)-2-decenal, 2.0 μg/L]. Pressing was found to be the critical process point for stress compound release, and additional pressing processes, press types, and press fractions were investigated. BMSB taint for white wines was not found to be problematic with respect to wine quality. An action control of 3 BMSB/cluster is recommended as this was related to the known consumption rejection threshold for (E)-2-decenal.