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In response to increasing concerns over climate change, soil health and wine quality, grape growers are seeking new practices (e.g., biochar application) to minimize their environmental footprint while increasing productivity and the quality of their products. To explore the potential of biochar-based amendments to achieve these goals in wine grape production, vineyard trials were established in the fall of 2018. Two Oregon sites were chosen with distinct soil types and climates (Willamette Valley and Rogue Valley) but planted with the same grapevine scion/rootstock Pinot noir combination. Four treatments were applied under vines at each location: no biochar-no tillage (NT); no biochar + tillage (B0); 18 tons ha−1 biochar + tillage (B18); 35 tons ha−1 biochar + tillage (B35). In 2019, a suite of soil health, plant, and crop variables were measured, and wines were produced after harvest. The incorporation of biochar modified the chemical and physical composition of soils at the two studied locations, increasing the bioavailability of carbon and nitrogen, their gravimetric water content and the concentration of plant available micro and macro nutrients. No responses of plant physiology parameters or productivity at either site were found after biochar incorporation when compared with controls. Conversely, a significant and gradual decrease in the amount of wine tannins was found as a result of biochar application in wines produced from grapes from the Woodhall location. Long-term field experiments are required to assess the effects of biochar on soil properties, vine physiology, productivity, and grape and wine quality several years after incorporation.

This study investigated the effect of select non-Saccharomyces yeast strains on Hanseniaspora uvarum growth and acetic acid and ethyl acetate production during prefermentation cold soak. We tested commercially available non-Saccharomyces yeasts for their ability to reduce H. uvarum growth and acetic acid production during a simulated cold soak in a grape juice-based medium. All tested non-Saccharomyces yeast reduced H. uvarum growth and acetic acid production, with some yeast having a greater impact than others. Following the screening of non-Saccharomyces yeast, we tested 14 different H. uvarum isolates against a selected non-Saccharomyces yeast, Metschnikowia fructicola, and found that all H. uvarum isolates had reduced growth and acetic acid production when grown in co-culture with M. fructicola, with variation between isolates noted. Finally, we evaluated the effect of M. fructicola on H. uvarum during prefermentation cold soak of Pinot noir grapes. Pinot noir grapes were inoculated with a combination of H. uvarum and M. fructicola and cold soaked for six days at 8°C. At the end of cold soaking, treatments inoculated with M. fructicola contained lower populations of H. uvarum and significantly lower acetic acid and ethyl acetate concentrations compared with treatments not inoculated with M. fructicola. After the completion of alcoholic fermentation, wines where M. fructicola was added contained significantly lower ethyl acetate but no differences in acetic acid concentration. These results suggest that adding select non-Saccharomyces yeast may be another method to reduce the risk of spoilage by H. uvarum during prefermentation cold soaking.

The potassium (K) requirements of Pinot noir grapevines were studied in a microplot vineyard, where four levels of fertilizer K supply were carefully controlled. Vine nutrient status, productivity, and must chemistry were studied over four years, and fermentation dynamics were evaluated over three years. Vine productivity, based on leaf area, pruning weights, and yield, was reduced by K supply only after four years in vines receiving no K fertilizer. K deficiency symptoms were apparent on leaves and fruit in vines receiving no K the year before productivity was altered, and after must pH was already reduced. Must pH was reduced below the level of control (100% K) vines in year 2, and thereafter in vines receiving no K, and also in years 3 and 4 in vines receiving 20% K. Late bunch stem necrosis occurred on some fruit clusters in year 3 in vines receiving no K and 20% K; this increased dramatically in year 4 in the no-K vines. Low must pH values of ~3.0 and must K concentrations as low as 600 mg K/L did not influence the rate of alcoholic fermentation. These findings indicate that monitoring must pH in addition to leaf blade or petiole K concentrations would be helpful in managing vine K status. A leaf blade K level of 6.0 g K/kg dry weight (DW) at veraison is proposed as the critical concentration for Pinot noir vines cropped at levels typical for the region. Growers should monitor vine K status closely and must pH when leaf blade K at veraison approaches 7.0 g K/kg DW in western Oregon Pinot noir vineyards to account for sampling and laboratory error.

Malolactic fermentation (MLF) is an important process in wine production due to the resulting reduction in acidity. MLF is typically induced by the addition of Oenococcus oeni after the completion of alcoholic fermentation (AF), but can occur concurrent with AF by co-inoculation of O. oeni with Saccharomyces cerevisiae. This study investigated the effect of MLF inoculation timing and temperature (15 &deg, C and 21 &deg, C) and the presence of the non-Saccharomyces yeast Torulaspora delbrueckii on Chardonnay wine aroma and mouthfeel. Aroma composition was measured using headspace solid-phase microextraction-gas chromatography mass spectrometry (HS-SPME-GCMS). Mouthfeel attributes of the wines produced were assessed by a winemaker panel, using Napping&reg, and Ultra-flash profiling. Significant differences in aroma composition and mouthfeel perception were found based on MLF timing and inoculation conditions, as well as between temperatures. Temperature had a greater impact on the aroma composition for sequential inoculations, while there were little differences based on the temperature of concurrent fermentations. Treatment type and temperature also affected the chemical composition of finished wines. Mouthfeel was impacted, although not as strongly as aroma composition. These findings demonstrate the usefulness of various MLF practices to influence the sensory qualities of a Chardonnay wine.

The genus Pediococcus comprises a group of nutritionally fastidious bacteria, several of which have been isolated from wines worldwide, for example P. damnosus, P. inopinatus, P. parvulus and P. pentosaceus. The growth of these bacteria is generally considered undesirable because of their ability to produce off‐odours and flavours. As examples, Pediococcus spp. have been associated with the synthesis of excessive diacetyl, exopolysaccharides, and/or biogenic amines, all of which have a detrimental impact on wine quality. Historically, oenological factors, such as low pH, high ethanol and nutrient depletion following malolactic fermentation, have often been considered sufficient to limit growth. Recent research, however, has supported the contention that Pediococcus spp. can grow in wines considered to be microbiologically stable. Furthermore, the presence of Pediococcus spp. in wines does not always lead to spoilage. New findings have suggested potential uses for Pediococcus spp. in winemaking, but have also highlighted a lack of understanding of those factors that influence growth and spoilage potential. The present work reviews the current knowledge of pediococci isolated during vinification as well as focuses on areas for future research.

A study to examine the phosphorus (P) requirements of Pinot noir was carried out using a microplot vineyard with carefully controlled P inputs. Pinot noir grafted onto 101-14 rootstock was exposed to four levels of P supply delivered via fertigation beginning in their fourth growing season. Vine nutrient status, productivity, and must chemistry were studied over four years (2012 to 2015), and fermentation dynamics were evaluated over three years (2012 to 2014). P supply primarily influenced vine productivity by reducing leaf area at veraison and by reducing yield, which occurred after three years in vines that received no P fertilizer. Flowering and fruit set were not altered by low P status. P supply had the most significant impact on must P levels, where the two lowest P supply treatments had reduced must P within the first year that P was altered. However, must P concentrations as low as 32 mg P/L did not affect the time needed for yeast to complete alcoholic fermentation. These findings suggest that limiting P reduces Pinot noir canopy size and yield before it alters flowering parameters or reduces must P concentrations sufficiently to alter fermentation. A P concentration of 1.0 g P/kg dry weight (DW) in leaf blades at veraison is proposed as the critical level below which growth and yield of Pinot noir are reduced when vines are cropped at levels typical for premium wine production in the region. Growers should closely monitor vine P status when leaf blade P at veraison approaches 1.2 g P/kg DW in western Oregon Pinot noir vineyards to account for sampling and laboratory error.

This work evaluated the impact of vine nitrogen (N), phosphorous (P), and potassium (K) supply on Pinot noir wine composition. Pinot noir grapevines were grown in a pot-in-pot system for three years and fertigated with varying levels of N, P, or K supply while holding all other nutrients constant. N was varied from 7.50 mM total N supply (Control) to as low as 1.125 mM total N in five discreet levels, while P and K supply were each varied in four levels, with the lowest rate (0 mM) during fertigation events. Wines produced in each of the three years were analyzed. N supply had a major impact on wine composition, including effects on volatile compounds, especially fermentation-derived esters and higher alcohols. Lower rates of N supply increased the total phenolic content in wine; in general, reduced N supply led to a decrease in straight-chain esters and alcohols, but to an increase in branched-chain esters and alcohols in wine. Low-N wines also had lower levels of volatile sulfur compounds in two of the three years. N supply also affected some grape-derived compounds in wine. Reducing N supply resulted in lower concentrations of β-damascenone across all years, but the effect of N supply on monoterpenes was not consistent from year to year. Altering P supply did not have reproducible effects on wine volatiles. Changes in volatile composition in response to nutrient supply could ultimately affect aroma perception and overall wine quality, which will require further exploration.

A study to reassess the nitrogen (N) requirements for Pinot noir was carried out using a pot-in-pot vineyard where N inputs were carefully controlled. Pinot noir grafted on 101-14 rootstock was exposed to five levels of N supply beginning in their fourth growing season, and vine productivity, berry chemistry, and must fermentation dynamics were studied over three years. N supply altered the N status of vines in accordance with expectations. Varying N had a greater impact on vegetative growth parameters than upon reproductive responses. For example, at veraison, leaf area of vines exposed to the three lowest rates of N was reduced in all years, but yield was only reduced at the lowest N rate in the first year and at the two lowest N rates in subsequent years. Fruitfulness and fruit set were reduced slightly by low N, while flower number of inflorescences was unaffected. Effects on berry maturity indices at harvest were generally small, but effects on must yeast assimilable nitrogen (YAN) concentrations were large. YAN was reduced from ~200 mg N/L in the Control to as low as 25 mg N/L at the lowest N rate after three years. Treatments with lower YAN required more time to complete alcoholic fermentation, particularly those with YAN below 100 mg N/L. However, all musts fermented to dryness. Reducing vegetative growth of Pinot noir can be achieved prior to reducing yield by reducing N status when vines are cropped at levels typical for premium wine production in the region. YAN levels as low as 100 mg N/L may be a better production target for wineries to achieve minimum fermentation requirements of Pinot noir.

Brettanomyces yeasts remain one of the most important spoilage issues facing the global wine industry. Despite their ubiquitous association with wine and wineries from around the world, there is almost no information on the occurrence of Brettanomyces in vineyards. In this study we used enrichment culturing to successfully isolate Brettanomyces yeasts from 12 of 149 grape berry cluster samples obtained from a vineyard in Oregon over two harvest seasons. This low rate of recovery was consistent with another recent study performed in Italy (Oro et al. 2019) and suggests that Brettanomyces is not a prevalent vineyard yeast genus. In addition to Brettanomyces, we recovered non-Saccharomyces isolates from a further 39 samples. These were predominantly from genera infrequently described in the context of vineyards and winemaking fungal communities, such as; Nakazawea, Kazachstania, Lodderomcyes and Ogataea. By evaluating relative growth capacity and direct competitive fitness, we show that while some vineyard non-Saccharomyces yeasts are likely to be out-competed in enrichment media by Brettanomyces, others can interfere with Brettanomyces recovery. This may partly explain why Brettanomyces vineyard populations are rarely described. Our results pave the way for further studies of Brettanomyces from non-fermentation origins, while also showing that enrichment culturing can be applied to reveal other rare vineyard yeast populations.

Yeasts isolated from a prefermentation cold maceration (at 8 to 9°C) of Vitis vinifera L. cv. Pinot noir grapes were evaluated for β-glucosidase activity. Among the 13 distinct yeast isolates investigated, five had β-glucosidase activity. Sequence analysis of the D1/D2 domain of the 26S rDNA gene confirmed the identity of these yeasts as Metschnikowia pulcherrima, Hanseniaspora uvarum, Lachancea thermotolerans, and two isolates of Saccharomyces cerevisiae. The β-glucosidase activity of these yeast isolates was further investigated at different sugar concentrations and temperatures before the isolates were used in the production of Pinot noir wines. Pinot noir grapes sterilized by high hydrostatic pressure were inoculated with the individual yeast species or a mixture of all yeast species. A seven day prefermentation cold maceration (9°C) was then performed, followed by alcoholic fermentation conducted by S. cerevisiae RC212 at 27°C. Pinot noir grapes were also cold-macerated without the addition of any yeast, while fermentations were also undertaken with no cold maceration. Solid-phase microextraction-gas chromatography-mass spectrometry analysis of the wines indicated that the presence of the different yeast species during the prefermentation cold-maceration altered the volatile aroma composition of the wines. These yeasts altered the concentrations of ethyl esters, branch-chained esters, higher alcohols, and some monoterpenes in the wines.

Pediococcus spp. were isolated from commercial wines from Oregon and Washington state, and the impacts of these isolates on the chemistry, microbiology, and sensory quality of Pinot noir wines were investigated. The pediococci isolates were inoculated into wines after alcoholic fermentation, and the wines were then chemically and sensorially analyzed after 60 days. All pediococci isolates partially degraded l-malic acid, with P. damnosus OW2 and P. parvulus OW7 completing malolactic fermentation (MLF). Despite having extensively large cell populations (>106 cfu/mL), the fermented wines had low concentrations of biogenic amines ( 5 mg/L). Production of d-lactic acid varied among the isolates, with strain OW7 producing the highest concentration (264 mg/L). Diacetyl concentrations also varied, with some wines containing low levels ( 15 mg/L). Furthermore, growth of some pediococci resulted in loss of red color and polymeric pigment content, potentially due to acetaldehyde degradation. Sensory analyses revealed differences in aroma (“floral”, “overall fruit”, “red fruit”, and “buttery”) and flavor (“sour” and “astringency”) among wines inoculated with different Pediococcus species or strains. Co-inoculation of P. parvulus and Brettanomyces bruxellensis resulted in wines having lower concentrations of 4-ethylphenol but reaching higher populations than in separate inoculations. This study has demonstrated the variability among Pediococcus species and strains in the production of various spoilage products and highlights the range of potential sensory effects these bacteria may have on a Pinot noir wine.

One factor potentially affecting growth of wine spoilage microbes (e.g., Pediococcus spp.) is the presence of nutrients not consumed during alcoholic fermentation by Saccharomyces cerevisiae. To assess the impact of must nutrient supplementation on Pediococcus spp., synthetic grape musts containing low (55.2 mg N/L), medium (250 mg N/L), or high (530 mg N/L) concentrations of yeast assimilable nitrogen (YAN) were fermented by S. cerevisiae. Upon cessation of fermentative activity P. damnosus OW-2, P. inopinatus OW-8, P. parvulus WS-7C, WS-29A, OW-1, or P. pentosaceus ATCC 33316 were inoculated at 104 to 105 cfu/mL. With the exceptions of OW-1 and OW-2, none of the other species or strains grew in the synthetic wines unless yeast extract or peptone was added, suggesting the absence of an essential nutrient. Experiments were replicated using Cabernet Sauvignon musts containing low (66.9 mg N/L), medium (219 mg N/L), and high (438 mg N/L) YAN. In general, wines containing the greatest residual amino acid concentrations (high YAN) supported better growth of the aforementioned Pediococcus spp. However, low YAN wines containing negligible residual nitrogen achieved similar populations after a short period of initial inhibition, suggesting that ‘excessive’ nitrogen supplementation to musts does not have a large impact on growth of pediococci post alcoholic fermentation.

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.

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.

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.

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.

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.

There are many interactions that occur between taste and aroma that may impact perception. The main objective of this study was to ascertain whether the aroma fraction of wine should be considered when investigating relationships between chemical composition and sensory perception of mouthfeel. Chardonnay wines with different mouthfeels were produced by altering the fermentation temperature (15 °C and 21 °C) of the alcoholic and malolactic fermentations (MLF) as well as the timing of MLF and the presence of a non-Saccharomyces yeast during alcoholic fermentation. Napping® and Ultra-flash-profiling were conducted using a panel of white winemakers. Each procedure was conducted twice: once with retro-nasal aroma (+R) and once without retronasal aroma (−R). Napping® results showed that retronasal aroma impacted mouthfeel perception. Ultra-flash profiling of +R and −R displayed similar descriptive terms used. Several terms appear to be related to retronasal aroma as they were used in +R and not in −R. It is unclear if these terms are due to interactions or due to associated learning. These results suggest that for some mouthfeel terms the volatile fraction plays a role and, to establish relationships between chemical composition and mouthfeel perception, it is important to consider both the volatile and nonvolatile wine fractions.

Background and Aims: The impact of yeast strain and species on the aroma and flavour of Pinot Noir wine was investigated using grapes treated with high hydrostatic pressure (HHP) to inactivate naturally occurring yeast and bacteria. Methods and Results: Pinot Noir grapes were treated by HHP resulting in inactivation of all viable yeast and bacterial cells. Grapes were then inoculated with either Saccharomyces cerevisiae RC212, Assmanshausen (AMH), MERIT.ferm, S. cerevisiae bayanus EC1118, or a blend of MERIT.ferm and Kluyveromyces thermotolerans (SYMPHONY). Descriptive analysis of wines revealed significant differences in overall fruity, red fruit, dark fruit, and jammy/cooked aromas. Principle component analysis showed wines produced by EC1118 and RC212 were characterized by higher dark fruit and jammy aromas while MERIT.ferm produced wine characterized by red fruit and floral aromas. Wines produced from AMH and SYMPHONY trended towards higher overall aged aromas and lower fruity and floral aromas. Conclusions: Yeast strain significantly impacted Oregon Pinot Noir wine aroma with some yeast strains producing wines with increased red and dark fruit aromas while others had reduced fruity aromas and higher aged aromas. Growth of Kluyveromyces thermotolerans during the early stages of fermentation resulted in a decrease in red fruity aromas. Significance of Study: Use of HHP in combination with sterile micro-fermentors allowed the impact of specific yeast on Pinot Noir aroma and flavor to be investigated. Differences in fruity aromas between Pinot Noir wines fermented by different yeast, including a non-Saccharomyces yeast, suggest that yeast strain and species can have a significant impact on Pinot Noir aroma.

Aims To investigate the impact of acetaldehyde- and pyruvic acid-bound sulphur dioxide on wine lactic acid bacteria (LAB). Methods and results Growth studies were performed where Oenococcus oeni, Pediococcus parvulus, Ped. damnosus and Lactobacillus hilgardii were inoculated into media containing various concentrations of acetaldehyde or pyruvic acid and an equimolar concentration of SO(2) at pH 3.50 and 3.70. Low concentrations of acetaldehyde- and pyruvic acid-bound SO(2) were inhibitory to the growth of all bacteria although acetaldehyde-bound SO(2) was generally more inhibitory than pyruvic acid-bound SO(2). Inhibition was greater at pH 3.50 than 3.70, and Lact. hilgardii was the most sensitive to acetaldehyde-bound SO(2), while O. oeni was the most sensitive to pyruvic acid-bound SO(2). Degradation of SO(2)-bound acetaldehyde was observed for all LAB, and aside from O. oeni, there was also complete degradation of SO(2)-bound pyruvic acid at both pH values. O. oeni only degraded pyruvic acid at pH 3.70. Degradation of SO(2)-bound acetaldehyde or pyruvic acid did not correlate with bacterial growth as inhibition was always observed in media containing bound SO(2). Conclusions Acetaldehyde- and pyruvic acid-bound SO(2) were inhibitory to wine LAB growth at concentrations as low as 5 mg l(-1). Despite this inhibition, all wine LAB degraded SO(2)-bound acetaldehyde and pyruvic acid suggesting that bound SO(2) may have a bacteriostatic rather than bacteriocidal action. Significance and impact of the study Sulphur dioxide bound to acetaldehyde or pyruvic acid is inhibitory to growth of wine LAB and must be considered when conducting the malolactic fermentation or controlling the growth of spoilage bacteria such as Pediococcus and Lactobacillus.

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.

Metabolic interactions between yeast assimilable nitrogen (YAN), biotin, pantothenic acid, and fermentation temperature that affect H2S production by wine yeast during alcoholic fermentation were examined. Strains of Saccharomyces cerevisiae (UCD 522 and EC1118) were inoculated into a synthetic grape juice medium with H2S evolution monitored under fermentative conditions. While a number of interactions affected the evolution of H2S, YAN as a factor by itself was found to be not significant (P > 0.05) for both yeasts examined. Maximal cumulative H2S production for strain UCD 522 occurred in media fermented at 30C with 60 mg/L YAN, 10 µg/L biotin, and 50 µg/L pantothenic acid while minimum production was observed with 250 mg/L YAN and 250 µg/L pantothenate. Similarly, strain EC1118 produced the most H2S at 30C, but with 250 mg/L YAN, 0.5 µg/L biotin, and 50 µg/L pantothenic acid and the least in media that contained 250 mg/L YAN and 250 µg/L pantothenic acid. PRACTICAL APPLICATIONS “Reduced” off-odors of wines, primarily associated with sulfur-containing molecules such as H2S, continue to be a difficulty facing winemakers worldwide. One strategy for wineries to limit these problems is to add yeast nutrients prior to fermentation, most commonly, nitrogen-containing compounds such as diammonium phosphate. However, nitrogen deficiency is not always the sole cause for these problems. Rather, the current research suggests the need to consider factors other than nitrogen including availability of biotin and pantothenic acid as well as fermentation temperature in order to minimize these off-odors.

Trans-2-decenal and tridecane are compounds found in wine made from brown marmorated stink bug (BMSB)-contaminated grapes. The effectiveness of post-fermentation processes on reducing their concentration in finished wine and their longevity during wine aging was evaluated. Red wines containing trans-2-decenal were treated with fining agents and put through reverse osmosis filtration. The efficacy of these treatments was determined using chemical analysis (MDGC-MS) and sensory descriptive analysis. Tridecane and trans-2-decenal concentrations in red and white wine were determined at bottle aging durations of 0, 6, 12 and 24 months using MDGC-MS. Reverse osmosis was found to be partially successful in removing trans-2-decenal concentration from finished wine. While tridecane and trans-2-decenal concentrations decreased during bottle aging, post-fermentative fining treatments were not effective at removing these compounds. Although French oak did not alter the concentration of tridecane and trans-2-decenal in red wine, it did mask the expression of BMSB-related sensory characters. Because of the ineffectiveness of removing BMSB taint post-fermentation, BMSB densities in the grape clusters should be minimized so that the taint does not occur in the wine.

Total protein and protein-associated mannan concentrations were measured, and individual proteins were identified during extraction into model wines over 9 months of aging on the yeast lees following completion of fermentations by seven wine strains of Saccharomyces cerevisiae. In aged wines, protein-associated mannan increased about 6-fold (+/-66%), while total protein only increased 2-fold (+/-20%), which resulted in a significantly greater protein-associated mannan/total protein ratio for three strains. A total of 219 proteins were identified among all wine samples taken over the entire time course. Of the 17 "long-lived" proteins detected in all 9 month samples, 13 were cell wall mannoproteins, and four were glycolytic enzymes. Most cytosolic proteins were not detected after 6 months. Native mannosylated yeast invertase was assayed for binding to wine tannin and was found to have a 10-fold lower affinity than nonglycosylated bovine serum albumin. Enrichment of mannoproteins in the aged model wines implies greater solution stability than other yeast proteins and the possibility that their contributions to wine quality may persist long after bottling.

The ability of different wine yeast (Saccharomyces cerevisiae) to inhibit malolactic bacteria (Oenococcus oeni) and the influence of nitrogen were studied using a synthetic grape juice. Malolactic fermentation was induced in fermenting synthetic grape juice or synthetic wines inoculated with different commercial strains of S. cerevisiae. O. oeni was generally inhibited in wines that contained higher concentrations of total SO2 although many yeast strains only inhibited the bacteria during fermentation under high nitrogen conditions. Yeast produced higher amounts of SO2 during fermentation under high nitrogen conditions suggesting that nitrogen affected the malolactic fermentation by influencing yeast SO2 production. However, the production of SO2 by yeast did not always account for the inhibition of O. oeni, suggesting the presence of other inhibitory mechanisms.

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.

The ability of Saccharomyces to inhibit Oenococcus oeni during the alcoholic fermentation by mechanisms other than SO(2) production was investigated. During fermentation in synthetic grape juice, S. cerevisiae strain RUBY.ferm inhibited the malolactic fermentation by O. oeni while strain EC1118 did not despite both strains producing similar amounts of SO(2). The bacterial inhibition exerted by RUBY.ferm was diminished when the wine was treated with proteases but not through the addition of nutrients. Wine fermented by RUBY.ferm was fractionated based on molecular weight and each fraction tested for the ability to inhibit the growth of O. oeni. The fraction containing compounds larger than 3 kDa was the sole inhibitory fraction. The inhibitory fraction was analyzed by SDS PAGE and showed a 5.9 kDa protein band present in wine fermented by RUBY.ferm that was not present in wine fermented by a non-antagonistic yeast, S. cerevisiae strain Saint Georges S101. The ability of the peptide to inhibit O. oeni seemed to be dependent on the presence of SO(2).

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. Methods and Results: Wines were produced by alcoholic fermentation with commercial yeast and adjusted to pH 3.3 and 3.6. While acetaldehyde was degraded rapidly and concurrently with malic acid at both pH values, SO2-bound acetaldehyde caused sluggish bacterial growth. Strain differences were small. Conclusions: Efficient degradation of acetaldehyde can be achieved by commercial starters of O. oeni. According to the results, the degradation of acetaldehyde could not be separated from malolactic conversion by oenococci. While this may be desirable in white winemaking, it may be necessary to delay malolactic fermentation (MLF) in order to allow for colour development in red wines. SO2-bound acetaldehyde itself maybe responsible for the sluggish or stuck MLF, and thus bound SO2 should be considered next to free SO2 in order to evaluate malolactic fermentability. Significance and Impact of the Study: The current study provides new results regarding the metabolism of acetaldehyde and SO2-bound acetaldehyde during the MLF in white wine. The information is of significance to the wine industry and may contribute to reducing the concentration of wine preservative SO2.

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.

Acetaldehyde is a volatile flavor compound present in many fermented foods and is important in the production of red and white wines. Nine strains of the genera Lactobacillus and Oenococcus were able to metabolize acetaldehyde in a resting cell system, whereas two Pediococcus strains were not. Acetic acid and ethanol were produced from its degradation. A Lactobacillus and an Oenococcus were able to degrade SO(2)-bound acetaldehyde, as well. A coincubation of resting cells of Saccharomyces bayanus Première Cuvée and Oenococcus oeni Lo111 showed that strain Lo111 metabolized acetaldehyde produced by the yeast. The ability of malolactic bacteria to degrade free and SO(2)-bound acetaldehyde has implications for sensory and color qualities and the use of SO(2) in wine.