Charles G. Edwards

The influence of nitrogen and biotin interactions on the performance of Saccharomyces in alcoholic fermentations.

Aim:  To study the impact of assimilable nitrogen, biotin and their interaction on growth, fermentation rate and volatile formation by Saccharomyces.

Advances in the Control of Wine Spoilage by Zygosaccharomyces and Dekkera/Brettanomyces

Understanding the characteristics of yeast spoilage, as well as the available control technologies, is vital to producing consistent, high-quality wine. Zygosaccharomyces bailii contamination may result in refermentation and CO2 production in sweet wines or grape juice concentrate, whereas Brettanomyces bruxellensis spoilage often contributes off-odors and flavors to red wines. Early detection of these yeasts by selective/differential media or genetic methods is important to minimize potential spoilage. More established methods of microbial control include sulfur dioxide, dimethyl dicarbonate, and filtration. Current research is focused on the use of chitosan, pulsed electric fields, low electric current, and ultrasonics as means to protect wine quality.

Identification and characterization of Dekkera bruxellensis, Candida pararugosa, and Pichia guilliermondii isolated from commercial red wines.

Yeast isolates from commercial red wines were characterized with regards to tolerances to molecular SO(2), ethanol, and temperature as well as synthesis of 4-ethyl-phenol/4-ethyl-guaiacol in grape juice or wine. Based on rDNA sequencing, nine of the 11 isolates belonged to Dekkera bruxellensis (B1a, B1b, B2a, E1, F1a, F3, I1a, N2, and P2) while the other two were Candida pararugosa (Q2) and Pichia guilliermondii (Q3). Strains B1b, Q2, and Q3 were much more resistant to molecular SO(2) in comparison to the other strains of Dekkera. These strains were inoculated (10(3)-10(4)cfu/ml) along with lower populations of Saccharomyces (<500 cfu/ml) into red grape juice and red wine incubated at two temperatures, 15 degrees C and 21 degrees C. Although Saccharomyces quickly dominated fermentations in grape juice, B1b and Q2 grew and eventually reached populations >10(5)cfu/ml. In wine, Q3 never entered logarithmic growth and quickly died in contrast to Q2 which survived >40 days after inoculation. B1b grew well in wine incubated at 21 degrees C while slower growth was observed at 15 degrees C. Neither Q2 nor Q3 produced 4-ethyl-phenol or 4-ethyl-guaiacol, unlike B1b. However, lower concentrations of volatile phenols were present in wine incubated at 15 degrees C compared to 21 degrees C.

Inducing malolactic fermentation in wines

Malolactic fermentation (MLF) in wine can be accomplished by relying on the natural microflora or by inducing through inoculation of a specific strain(s) of malolactic bacteria, primarily strains of Leuconostoc oenos. Problems with inducing MLF include intrinsic factors of the grape must such as pH, presence of sulfur dioxide, and ethanol in addition to antagonism of malolactic bacteria by wine yeast. Current methods and new technology to improve the predictability of MLF are discussed.

Impact of available nitrogen and sugar concentration in musts on alcoholic fermentation and subsequent wine spoilage by Brettanomyces bruxellensis.

The level of yeast assimilable nitrogen (YAN) supplementation required for Saccharomyces cerevisiae to complete fermentation of high sugar musts in addition to the impact of non-metabolized nitrogen on post-alcoholic spoilage by Brettanomyces bruxellensis was studied. A 2 × 3 factorial design was employed using a synthetic grape juice medium with YAN (150 or 250 mg N/L) and equal proportions of glucose/fructose (230, 250, or 270 g/L) as variables. S. cerevisiae ECA5 (low nitrogen requirement) or Uvaferm 228 (high nitrogen requirement) were inoculated at 10(5) cfu/mL while B. bruxellensis E1 or B2 were added once alcoholic fermentation ceased. Regardless of YAN concentration, musts that contained 230 or 250 g/L glucose/fructose at either nitrogen level attained dryness (mean = 0.32 g/L fructose) while those containing 270 g/L generally did not (mean = 2.5 g/L fructose). Higher concentrations of YAN present in musts yielded wines with higher amounts of α-amino acids and ammonium but very little (≤ 6 mg N/L) was needed by B. bruxellensis to attain populations ≥ 10(7) cfu/mL. While adding nitrogen to high sugar musts does not necessarily ensure completion of alcoholic fermentation, residual YAN did not affect B. bruxellensis growth as much as ethanol concentration.

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.

Changes in color and sugar content of yellow-fleshed potatoes stored at three different temperatures

Yellow-fleshed potatoes, Yukon Gold, Red Gold, Sag-maw Gold, Augsberg Gold, and AO82283.1 were compared to white-fleshed cultivars, Russet Burbank and Norchip, in relation to flesh color and sugar content during long-term storage. Yellow-fleshed cultivars had higher hue angles (h°) and chroma values (C*) compared to the white-fleshed potatoes. These values were consistently higher at all storage temperatures. Chroma values were maximum for most yellow-fleshed tubers when stored at 8.3 C for 84 days. As expected, lower concentrations of sucrose, glucose, and fructose were observed in tubers stored at 10 C compared to those stored at 3.3 and 8.3 C. After storage at either 3.3 or 8.3 C, Saginaw Gold, Augs-berg Gold, and AO82283.1 accumulated lower amounts of glucose or fructose compared to Norchip, Russet Burbank, Yukon Gold, and Red Gold. Although the yellow-fleshed clones accumulated up to 7.4 mg/g glucose or fructose when stored at 3.3 C, Saginaw Gold and Augsberg Gold responded well to reconditioning.

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.

Cost Economies and Economic Impacts of Pricing and Product Mix Decisions in Premium Table Wine Wineries

Investments and operating costs in wineries producing premium table wines ranging in size from 2000 to 500 000 cases (one case = 12 bottles of 750 ml capacity) were estimated. The wineries, which were 200 000 cases or more, produced generic table wines. The initial investment costs ranged from

Application of a New Yeast Preparation for Problem Grape Musts

451 170 (US dollars) to