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Protein stability is an important quality attribute in wines and protein haze will lead to consumer rejection. Traditionally, stability is achieved by bentonite addition; however, environmental concerns and disposal problems mean that alternatives are required to achieve the same goal. In this study, the use of Sacharomyces paradoxus, chitosan, polystyrene, carboxymethyl cellulose, and bentonite were evaluated. Trials in finished wines were agitated for 10 h overnight and analyzed for turbidity and color characteristics spectrophotometrically. Experiments were conducted with wines that are expected to develop protein instabilities, Muscat Canelli, White Zinfandel, Cabernet Sauvignon blanc de noir, Barbera rosé, and Touriga Nacional. Results indicate that S. paradoxus can help with the removal of proteins from wine. Wines with low protein instability can be stabilized with S. paradoxus as well as polystyrene and chitosan to a lesser degree. All fining agents except for bentonite show efficiency variability between white and red wines. With an average protein reduction around 50%, none of the alternative fining methods could reach the efficiency level of bentonite. Experiments in a model system confirm the findings and explain some of the mechanisms involved, for example the specificity of chitosan and challenges related to the use of yeast as a fining agent.
Stephan Sommer; Federico Tondini. Sustainable Replacement Strategies for Bentonite in Wine Using Alternative Protein Fining Agents. Sustainability 2021, 13, 1860 .
AMA StyleStephan Sommer, Federico Tondini. Sustainable Replacement Strategies for Bentonite in Wine Using Alternative Protein Fining Agents. Sustainability. 2021; 13 (4):1860.
Chicago/Turabian StyleStephan Sommer; Federico Tondini. 2021. "Sustainable Replacement Strategies for Bentonite in Wine Using Alternative Protein Fining Agents." Sustainability 13, no. 4: 1860.
Throughout fermentation, yeast faces continuously changing medium conditions and reacts by adapting its metabolism. The adaptation is a critical process and is dependent on the accurate functioning of the cell. A stable membrane potential, which is, among other roles, responsible for protecting the yeast from low pH, is an important attribute for evaluating functionality. Other factors are storage products such as glycogen, trehalose, and neutral lipids, as well as mitochondrial activity and the integrity of the DNA. These parameters can be complemented by the analysis of viability, cell cycle, intracellular pH, and reactive oxygen species in the cell. The correlation of all these factors provides valuable information for evaluating the performance of a yeast population during fermentation. In order to demonstrate the analytical capabilities of flow cytometry, a Saccharomyces cerevisiae yeast strain was observed in a modified growth medium for 384 h (16 days). The results confirm observations made with other methods and reports from the literature. However, with flow cytometry, it is possible to gain deeper insight into stress response and adaptation behavior of yeast at a cellular level. The causality from the formation of oxygen-radicals to cell death, for example, can be shown, as well as the dependency of the intracellular pH on the stability of the membrane. The proposed bio-monitoring system has the potential to provide applicable information as a process control tool for wineries.
Stephan Sommer. Monitoring the Functionality and Stress Response of Yeast Cells Using Flow Cytometry. Microorganisms 2020, 8, 619 .
AMA StyleStephan Sommer. Monitoring the Functionality and Stress Response of Yeast Cells Using Flow Cytometry. Microorganisms. 2020; 8 (4):619.
Chicago/Turabian StyleStephan Sommer. 2020. "Monitoring the Functionality and Stress Response of Yeast Cells Using Flow Cytometry." Microorganisms 8, no. 4: 619.
Copper in grape musts can influence the fermentation efficiency of Saccharomyces cerevisiae during winemaking. The present study revealed the impact of glutathione addition on yeast strains with variable copper sensitivity. The antioxidant glutathione increased yeast vitality and fastened sugar metabolism at copper concentrations up to 0.39 mM. A significant accumulation of acetaldehyde at high copper concentrations was mitigated by the addition of 20 mg L-1 glutathione. Low recovery of glutathione added implicated a complexation of both compounds. Specific alcohol dehydrogenase (ADH) activity was inhibited or reduced in the enzyme extracts of the copper-stressed yeast cells. The activity was restored in fermentations with glutathione at a copper concentration of 0.16 mM. At low copper concentrations, glutathione decreased ADH activity presumably due to complexation of essential copper amounts. Results provide important information on the use of glutathione as an antioxidant in winemaking to counteract negative effects of copper-rich musts on copper-sensitive yeast strains.
Sabrina Zimdars; Lukas Schrage; Stephan Sommer; Andreas Schieber; Fabian Weber. Influence of Glutathione on Yeast Fermentation Efficiency under Copper Stress. Journal of Agricultural and Food Chemistry 2019, 67, 10913 -10920.
AMA StyleSabrina Zimdars, Lukas Schrage, Stephan Sommer, Andreas Schieber, Fabian Weber. Influence of Glutathione on Yeast Fermentation Efficiency under Copper Stress. Journal of Agricultural and Food Chemistry. 2019; 67 (39):10913-10920.
Chicago/Turabian StyleSabrina Zimdars; Lukas Schrage; Stephan Sommer; Andreas Schieber; Fabian Weber. 2019. "Influence of Glutathione on Yeast Fermentation Efficiency under Copper Stress." Journal of Agricultural and Food Chemistry 67, no. 39: 10913-10920.
Protein-polyphenol interactions play a very important role in wine stability assessment, especially in red varieties. Different polysaccharides can influence these interactions by protecting or disrupting charges and are even used as additives to stabilize colloidal solutions. The most common examples are mannoproteins and carboxymethyl cellulose (CMC). In some cases, the mechanisms that are involved in these reactions are not thoroughly understood and can lead to unexpected problems and delayed haze formation after CMC addition to red wines. Small scale bench-trials were conducted in model systems under different pH-conditions to monitor the formation of turbidity and protection mechanisms during the interaction of proteins, polyphenols, and polysaccharides. Egg-white protein was chosen as a protein model due to its complex composition, a commercial grape tannin extract was used as polyphenol source, and pectin, glucomannan, mannoprotein, alginate, and CMC were applied as polysaccharides to model various wine conditions. Reactions were monitored in duplicate on a 50 mL scale by spectrophotometry at 860 nm over at least 30 days. Some of the polysaccharides interacted directly with proteins or polyphenols causing precipitation. Other polysaccharides delayed the reaction between proteins and other macromolecules depending on their concentration. The results of these experiments provide important insight into reaction dynamics between macromolecules that are involved in the physical stability of wine.
Stephan Sommer; Fabian Weber; James F. Harbertson. Polyphenol–Protein–Polysaccharide Interactions in the Presence of Carboxymethyl Cellulose (CMC) in Wine-Like Model Systems. Journal of Agricultural and Food Chemistry 2019, 67, 7428 -7434.
AMA StyleStephan Sommer, Fabian Weber, James F. Harbertson. Polyphenol–Protein–Polysaccharide Interactions in the Presence of Carboxymethyl Cellulose (CMC) in Wine-Like Model Systems. Journal of Agricultural and Food Chemistry. 2019; 67 (26):7428-7434.
Chicago/Turabian StyleStephan Sommer; Fabian Weber; James F. Harbertson. 2019. "Polyphenol–Protein–Polysaccharide Interactions in the Presence of Carboxymethyl Cellulose (CMC) in Wine-Like Model Systems." Journal of Agricultural and Food Chemistry 67, no. 26: 7428-7434.
Red wines ferment in contact with skins to extract polyphenols and anthocyanins that help build, establish, and stabilize color. Concentration and composition vary among genera, species, and cultivars. For this study, 11 grapes representing Vitis vinifera (Cabernet Sauvignon, Merlot, Cabernet Franc, Barbera, Syrah, Petite Sirah, Mourvedre), Vitis labrusca (Concord), Muscadinia rotundifolia (Noble), and French-American hybrids (Marquette, Chambourcin) were selected. All cultivars were fermented on skins while color extraction was monitored daily. Each grape was also extracted using six different methods (microwave, and ultrasound assisted, Glorie procedure, ITV Standard (Institut Technique de la Vigne et du Vin), AWRI method (Australian Wine and Research Institute), solvent extraction of skins) and compared to color characteristics of the wines produced by fermentation. Results show that the extraction pattern varies among cultivars. Post-fermentation maceration, pressing, and sulfur dioxide addition lead to color loss up to 68 percent of the original maximum with the highest loss for native American grapes and hybrid varieties. Extraction procedures over-estimate color in the finished wine but are more accurate if compared to peak extraction levels during fermentation. Color loss and suitability of different extraction procedures to predict color characteristics of fermented wine strongly depend on the complexity of the anthocyanin spectrum and therefore the cultivar used.
Stephan Sommer; Seth D. Cohen. Comparison of Different Extraction Methods to Predict Anthocyanin Concentration and Color Characteristics of Red Wines. Fermentation 2018, 4, 39 .
AMA StyleStephan Sommer, Seth D. Cohen. Comparison of Different Extraction Methods to Predict Anthocyanin Concentration and Color Characteristics of Red Wines. Fermentation. 2018; 4 (2):39.
Chicago/Turabian StyleStephan Sommer; Seth D. Cohen. 2018. "Comparison of Different Extraction Methods to Predict Anthocyanin Concentration and Color Characteristics of Red Wines." Fermentation 4, no. 2: 39.
A novel method for the sensory evaluation of wine and cider is proposed that combines advantages of other commonly used techniques while simplifying a tasting protocol that is more accessible for unexperienced panelists. The method is based on panelist’s evaluation of samples in three discrete and directed steps; evaluation of head, heart, and base characters. The technique provides the sensory analyst with a simplified approach to difference testing and, in many instances, helps statistically differentiate samples by reducing panelist confusion. The head aroma is defined as the first impression after removing the lid from a covered glass prior to agitating the sample. The heart aroma is defined as the primary impression after agitating the sample. The base character is defined as the final aroma impression and retronasal evaluation of the product. Each component is evaluated independently using a generalized grouping of descriptors; sensory impression or grouping descriptors can be refined if the analyst aims to draw a higher level of detail or descriptive analysis from their panel. Application of the proposed analytical protocol suggests that the technique is simple for less-experienced panelists to learn and follow, and allowed them to easily focus on the testing attributes with minimal confusion of confounding factors.
Stephan Sommer; Stella J. Sommer; Seth D. Cohen. Proposal of thehead-heart-basetechnique as an innovative method to describe and evaluate the aroma profile of wine and cider. Journal of Wine Research 2018, 29, 204 -219.
AMA StyleStephan Sommer, Stella J. Sommer, Seth D. Cohen. Proposal of thehead-heart-basetechnique as an innovative method to describe and evaluate the aroma profile of wine and cider. Journal of Wine Research. 2018; 29 (3):204-219.
Chicago/Turabian StyleStephan Sommer; Stella J. Sommer; Seth D. Cohen. 2018. "Proposal of thehead-heart-basetechnique as an innovative method to describe and evaluate the aroma profile of wine and cider." Journal of Wine Research 29, no. 3: 204-219.
Most yeast and bacteria in wine are able to metabolize hydroxycinnamic acids into volatile phenols via enzyme-mediated decarboxylation. Our trials performed in wine and model systems suggest that lysozyme addition prior to fermentation affects both bacterial activity and the release of hydroxycinnamic acids from their tartrate esters. This increases the potential for volatile phenol formation, as microorganisms can only metabolize free hydroxycinnamates. Wines with delayed malolactic fermentation due to lysozyme addition contained significantly higher concentrations of free hydroxycinnamic acids and elevated levels of volatile phenols in some cases. The reason for this is likely related to the side activity of lysozyme in combination with a detoxification mechanism that only occurs under stressful conditions for the yeast. Experiments in model systems indicate that lysozyme can affect the yeast at a pH higher than usually found in wine by attacking chitin in the bud scars of the cell walls and therefore weakening the cell structure. Free hydroxycinnamates can also affect yeast viability, making an increased release during fermentation problematic for a successful fermentation.
Stephan Sommer; Pascal Wegmann-Herr; Michael Wacker; Ulrich Fischer. Influence of Lysozyme Addition on Hydroxycinnamic Acids and Volatile Phenols during Wine Fermentation. Fermentation 2018, 4, 5 .
AMA StyleStephan Sommer, Pascal Wegmann-Herr, Michael Wacker, Ulrich Fischer. Influence of Lysozyme Addition on Hydroxycinnamic Acids and Volatile Phenols during Wine Fermentation. Fermentation. 2018; 4 (1):5.
Chicago/Turabian StyleStephan Sommer; Pascal Wegmann-Herr; Michael Wacker; Ulrich Fischer. 2018. "Influence of Lysozyme Addition on Hydroxycinnamic Acids and Volatile Phenols during Wine Fermentation." Fermentation 4, no. 1: 5.
The aim of this study was to identify the source of haze formation in red wine after the addition of carboxymethyl cellulose (CMC) and to characterize the dynamics of precipitation. Ninety commercial wines representing eight grape varieties were collected, tested with two commercial CMC products, and analyzed for susceptibility to haze formation. Seventy-four of these wines showed a precipitation within 14 days independent of the CMC product used. The precipitates of four representative samples were further analyzed for elemental composition (CHNS analysis) and solubility under different conditions to determine the nature of the solids. All of the precipitates were composed of approximately 50% proteins and 50% CMC and polyphenols. It was determined that the interactions between CMC and bovine serum albumin are pH dependent in wine-like model solution. Furthermore, it was found that the color loss associated with CMC additions required the presence of proteins and cannot be observed with CMC and anthocyanins alone.
Stephan Sommer; Christian Dickescheid; James F. Harbertson; Ulrich Fischer; Seth D. Cohen. Rationale for Haze Formation after Carboxymethyl Cellulose (CMC) Addition to Red Wine. Journal of Agricultural and Food Chemistry 2016, 64, 6879 -6887.
AMA StyleStephan Sommer, Christian Dickescheid, James F. Harbertson, Ulrich Fischer, Seth D. Cohen. Rationale for Haze Formation after Carboxymethyl Cellulose (CMC) Addition to Red Wine. Journal of Agricultural and Food Chemistry. 2016; 64 (36):6879-6887.
Chicago/Turabian StyleStephan Sommer; Christian Dickescheid; James F. Harbertson; Ulrich Fischer; Seth D. Cohen. 2016. "Rationale for Haze Formation after Carboxymethyl Cellulose (CMC) Addition to Red Wine." Journal of Agricultural and Food Chemistry 64, no. 36: 6879-6887.
The aim of this study was to identify and evaluate factors that contribute to fermentation problems inChardonnay, since this variety is reported to have frequent problems. Analytical methods included gaschromatography mass spectrometry, as well as atomic absorption spectroscopy and FT-MIR spectroscopy.Chardonnay, Pinot blanc, Pinot noir and Pinot noir précoce were screened to relate observations to specificvarietal properties. The results show a significant distinction in the amino acid profile of Chardonnay,which can be correlated with sluggish fermentation. A comparison between the fatty acid profile ofChardonnay and Pinot blanc reveals that Chardonnay contains more toxic compounds, which inhibityeast metabolism. Mineral supply and potential metal toxicity were also analysed. The concentrationsof iron, copper, magnesium, zinc and manganese show significant variations among the grape varieties.In conclusion, the possible causes for stuck fermentation in Chardonnay could be more related more tovariety than to oenological decisions.
S. Sommer; P. Wegmann-Herr; M. Wacker; U. Fischer Fischer. Rationale for a Stronger Disposition of Chardonnay Wines for Stuck and Sluggish Fermentation. South African Journal of Enology and Viticulture 2015, 36, 1 .
AMA StyleS. Sommer, P. Wegmann-Herr, M. Wacker, U. Fischer Fischer. Rationale for a Stronger Disposition of Chardonnay Wines for Stuck and Sluggish Fermentation. South African Journal of Enology and Viticulture. 2015; 36 (1):1.
Chicago/Turabian StyleS. Sommer; P. Wegmann-Herr; M. Wacker; U. Fischer Fischer. 2015. "Rationale for a Stronger Disposition of Chardonnay Wines for Stuck and Sluggish Fermentation." South African Journal of Enology and Viticulture 36, no. 1: 1.
Stephan Sommer; Pascal Wegmann-Herr; Ulrich Fischer. Correlating the need for bentonite fining in wine with anomalous weather patterns. Journal of Wine Research 2014, 26, 29 -39.
AMA StyleStephan Sommer, Pascal Wegmann-Herr, Ulrich Fischer. Correlating the need for bentonite fining in wine with anomalous weather patterns. Journal of Wine Research. 2014; 26 (1):29-39.
Chicago/Turabian StyleStephan Sommer; Pascal Wegmann-Herr; Ulrich Fischer. 2014. "Correlating the need for bentonite fining in wine with anomalous weather patterns." Journal of Wine Research 26, no. 1: 29-39.
Pyruvate is the central metabolite in diacetyl synthesis by Oenococcus oeni. Therefore, any substrate, which increases intracellular pyruvate concentration, can induce diacetyl accumulation. This study evaluates the effect of exogenous pyruvate on diacteyl formation and the expression of diacetyl related genes in Oenococcus oeni during winemaking. Diacetyl formation by Oenococcus oeni was induced by yeast derived pyruvate in the early stage of winemaking Furthermore, when additional pyruvate was added, α-acetolactate synthase (alsS) gene expression raised 1.6-fold and the diacetyl concentration increased from 0.4 mg/L to 2.3 mg/L. Although the highest alsS expression (10-fold) was found 24 h after pyruvate addition, no further increase in diacetyl concentration was found. In addition to that alsD was also overexpressed (9-fold) at that point, indicating that α-acetolactate was converted into acetoin. Altogether the results show that exogenous pyruvate induces diacetyl formation by Oenococcus oeni in the early state of winemaking. Furthermore pyruvate derived diacetyl is the result of a delayed alsD response which prevents acetoin formation.
R. Mink; Ralf Kölling; S. Sommer; Hans-Georg Schmarr; M. Scharfenberger-Schmeer. Diacetyl Formation by Oenococcus oeni during Winemaking Induced by Exogenous Pyruvate. American Journal of Enology and Viticulture 2014, 66, 85 -90.
AMA StyleR. Mink, Ralf Kölling, S. Sommer, Hans-Georg Schmarr, M. Scharfenberger-Schmeer. Diacetyl Formation by Oenococcus oeni during Winemaking Induced by Exogenous Pyruvate. American Journal of Enology and Viticulture. 2014; 66 (1):85-90.
Chicago/Turabian StyleR. Mink; Ralf Kölling; S. Sommer; Hans-Georg Schmarr; M. Scharfenberger-Schmeer. 2014. "Diacetyl Formation by Oenococcus oeni during Winemaking Induced by Exogenous Pyruvate." American Journal of Enology and Viticulture 66, no. 1: 85-90.
Diacetyl accumulation in wine, which has undergone malolactic fermentation by Oenococcus oeni, is often associated with aromatic off‐flavours. Characterisation of the diacetyl‐related metabolic pathway helps to explain bacterial diacetyl formation during winemaking. The present study describes the time‐dependent formation of diacetyl during the vinification process after simultaneous, induced malolactic fermentation by freeze‐dried O. oeni on the basis of gene‐expression analysis of the citrate‐ and pyruvate‐derived pathways. After simultaneously induced malolactic fermentation in Pinot Blanc by O. oeni, the dynamics of diacetyl formation were compared with citrate consumption and gene‐expression of the diacetyl‐related metabolic pathways. Diacetyl concentration showed two maxima: the first increase was primarily influenced by the activity of Saccharomyces cerevisiae; however, the second increase was induced only by O. oeni and correlates with bacterial citrate degradation. Expression of the alsS gene showed two significant responses; however, only the second response was affected by the citrate‐associated genes maeP and citE. Additionally, alsD and butA2 were found to be continuously underexpressed during the winemaking process. Taken together, we suggest that diacetyl accumulation during the vinification process by O. oeni is affected by citrate fermentation. The diacetyl‐related alsS gene, however, is also overexpressed independently by other substrates, which may also increase the intracellular pyruvate level resulting in diacetyl formation. Characterisation of the time‐dependent diacetyl accumulation and its degradation during the vinification process is essential for the development of strategies that focus on the suppression of the diacetyl concentration below the sensory threshold.
R. Mink; Stephan Sommer; R. Kölling; Hans-Georg Schmarr; M. Scharfenberger-Schmeer. Time course of diacetyl formation during vinification withSaccharomyces cerevisiaeandOenococcus oenico-cultivation. Australian Journal of Grape and Wine Research 2014, 20, 194 -198.
AMA StyleR. Mink, Stephan Sommer, R. Kölling, Hans-Georg Schmarr, M. Scharfenberger-Schmeer. Time course of diacetyl formation during vinification withSaccharomyces cerevisiaeandOenococcus oenico-cultivation. Australian Journal of Grape and Wine Research. 2014; 20 (2):194-198.
Chicago/Turabian StyleR. Mink; Stephan Sommer; R. Kölling; Hans-Georg Schmarr; M. Scharfenberger-Schmeer. 2014. "Time course of diacetyl formation during vinification withSaccharomyces cerevisiaeandOenococcus oenico-cultivation." Australian Journal of Grape and Wine Research 20, no. 2: 194-198.
Microbially derived diacetyl accumulation during vinification imparts a buttery wine aroma, which has stylistic implications. However, at higher concentrations diacetyl induces an aromatic off‐flavour. Saccharomyces cerevisiae is able to reduce diacetyl to below the sensory threshold. Therefore, characterization of the diacetyl reduction in commercial wine yeasts creates new opportunities to manage the risk of wine associated off‐flavours. Diacetyl reduction by two commercial S. cerevisiae strains was characterized in Pinot blanc grape must of the vintage 2012 with different initial diacetyl concentrations (0–50 mg/L). Highest diacetyl reduction was found in the first two days after wine yeasts were inoculated. No further decrease in diacetyl content was observed after the fourth day. All assays in which diacetyl was added showed the same final diacetyl concentration of approximately 2 mg/L. However, a significantly lower amount of diacetyl was found in grape must without adding diacetyl. The present results indicate that commercial wine yeasts are able to reduce much higher amounts of diacetyl than normally expected during the vinification procedure. However, the constant final diacetyl concentration indicates that diacetyl accumulation may be the result of wine matrix binding effects, which prevent a complete reduction by active wine yeasts. Copyright © 2013 The Institute of Brewing & Distilling.
Roman Mink; Stephan Sommer; Ralf Kölling; Hans-Georg Schmarr; Louis Baumbach; Maren Scharfenberger-Schmeer. Diacetyl reduction by commercialSaccharomyces cerevisiaestrains during vinification. Journal of the Institute of Brewing 2013, 120, 23 -26.
AMA StyleRoman Mink, Stephan Sommer, Ralf Kölling, Hans-Georg Schmarr, Louis Baumbach, Maren Scharfenberger-Schmeer. Diacetyl reduction by commercialSaccharomyces cerevisiaestrains during vinification. Journal of the Institute of Brewing. 2013; 120 (1):23-26.
Chicago/Turabian StyleRoman Mink; Stephan Sommer; Ralf Kölling; Hans-Georg Schmarr; Louis Baumbach; Maren Scharfenberger-Schmeer. 2013. "Diacetyl reduction by commercialSaccharomyces cerevisiaestrains during vinification." Journal of the Institute of Brewing 120, no. 1: 23-26.