Yeast Fermentation Performance Research Articles

Impact of Natural Phytosanitary Product Residuals on Yeast Fermentation Performance and Wine Composition.

Although phytosanitary treatments are necessary to protect grapes from parasitic diseases, consumers are increasingly concerned about the use of synthetic phytosanitary products and their possible residues in wine. Pre-harvest phytosanitary treatments are often inevitable, and consequently downtime is required to avoid possible residues on the grapes. Instead, natural phytosanitary products, such as essential oil (EO)-based products, can be applied close to the harvest without specific restrictions, with results that are not only technically convenient but also more attractive for the consumers. Because of the high antimicrobial activity of EO products, in the present study we evaluated the effect of different residual amounts of two new EO-based phytosanitary products on the alcoholic fermentation and the chemical composition of the final fermented products. In particular, two EO-based new formulations, exploitable in organic viticulture management, were evaluated. Increasing concentrations of each formulation were tested during laboratory scale fermentations and in comparison with synthetic and natural commercial phytosanitary products. Growth and fermentation kinetics of a commercial yeast strain of Saccharomyces cerevisiae and the chemical and sensory profiles of the final products were evaluated. Both new formulations showed no significant impact on the growth and fermentation kinetic of S. cerevisiae at any of the concentrations tested. In all trials, alcoholic fermentation was completed in 15 days. Instead, a different chemical composition of the final products was observed. Therefore, these new products might represent an interesting alternative tool to the conventional phytosanitary treatments, being applicable close to the harvest without negative impacts on the kinetics of alcoholic fermentation and also being more acceptable to wine consumers.

Assessing the physiological properties of baker's yeast based on single-cell Raman spectrum technology

With rapid progress in the yeast fermentation industry, a comprehensive commercial yeast quality assessment approach integrating efficiency, accuracy, sensitivity, and cost-effectiveness is required. In this study, a new yeast quality assessment method based on single-cell Raman technology was developed and contrasted with traditional methods. The findings demonstrated significant associations (Pearson correlation coefficient of 0.933 on average) between the two methods in measuring physiological indicators, including cell viability and intracellular trehalose content, demonstrating the credibility of the Raman method compared to the traditional method. Furthermore, the sensitivity of the Raman method in viable but non-culturable cells was higher in measuring yeast cell viability (17.9 % more sensitive). According to the accurate quantitative analysis of metabolic activity level (MAL) of yeast cells, the cell vitality was accurately quantified at population and single-cell levels, offering a more comprehensive assessment of yeast fermentation performance. Overall, the single-cell Raman method integrates credibility, feasibility, accuracy, and sensitivity in yeast quality assessment, offering a new technological framework for quality assessments of live-cell yeast products.

Different Nitrogen Consumption Patterns in Low Temperature Fermentations in the Wine Yeast Saccharomyces cerevisiae.

Nowadays, the wine industry carries out fermentations at low temperatures because this oenological practice clearly improves the aromatic complexity of the final wines. In addition, nitrogen content of the must also influences the quality of the wine. In this study, we carried out a phenotypic and fermentative analysis of two industrial wine Saccharomyces cerevisiae strains (P5 and P24) at 15 and 28 °C and three nitrogen concentrations (60, 140 and 300 mg N/L) in synthetic must. Our results show that both parameters, temperature and nitrogen, are interrelated and clearly determine the competitiveness of the wine strains and their ability to adapt at low temperatures. The best adapted strain at low temperatures decreased its competitiveness at lower nitrogen concentrations. In addition, our results show that it is not only the quantity of nitrogen transported that is important but also the quality of the nitrogen source used for wine yeast adaptation at low temperatures. The presence of some amino acids, such as arginine, branched chain amino acids, and some aromatic amino acids can improve the growth and fermentation activity of wine yeasts at low temperatures. These results allow us to better understand the basis of wine yeast adaptation to fermentation conditions, providing important information for winemakers to help them select the most appropriate yeast strain, thus reducing the economic costs associated with long and sluggish fermentations. The correlation between some amino acids and better yeast fermentation performance could be used in the future to design inactive dry yeast enriched in some of these amino acids, which could be added as a nutritional supplement during low temperature fermentations.

Antibiofilm Effect of Curcumin on Saccharomyces boulardii during Beer Fermentation and Bottle Aging.

In a prior study, we elucidated the biofilm formation of Saccharomyces boulardii on glass surfaces during beer bottle aging. Here, we supplemented brewing wort with curcumin at 25 μg/mL concentration to mitigate S. boulardii biofilm and enhance beer's functional and sensory attributes. An assessment encompassing biofilm growth and development, fermentation performance, FLO gene expression, yeast ultrastructure, bioactive content, and consumer acceptance of the beer was conducted throughout fermentation and aging. Crystal violet (CV) and XTT reduction assays unveiled a significant (p < 0.05) reduction in biofilm formation and development. Fluorescent staining (FITC-conA) and imaging with confocal laser scanning microscopy provided visual evidence regarding reduced exopolysaccharide content and biofilm thickness. Transcriptional analyses showed that key adhesins (FLO1, FLO5, FLO9, and FLO10) were downregulated, whereas FLO11 expression remained relatively stable. Although there were initial variations in terms of yeast population and fermentation performance, by day 6, the number of S. boulardii in the test group had almost reached the level of the control group (8.3 log CFU/mL) and remained stable thereafter. The supplementation of brewing wort with curcumin led to a significant (p < 0.05) increase in the beer's total phenolic and flavonoid content. In conclusion, curcumin shows promising potential for use as an additive in beer, offering potential antibiofilm and health benefits without compromising the beer's overall characteristics.

Quantitative analysis perspective: Ice growth and super-chilling state of frozen dough under quick freezing

Ice crystal growth and dough quality under quick freezing were investigated in this study. The ice growth state (content and location) was analysed by the enthalpy balance method and electron microscopy analysis. The superchilling state was judged based on the quantitative analysis of ice crystals. The yeast fermentation performance and dough rheological properties of the frozen dough were assessed. The results showed that the −40 and −80 °C treatments led to quick dough freezing compared with the −20 °C freezing condition. Superchilled dough could be created at −40 °C (less than 35 min) or −80 °C (20 min). The yeast is intolerant to low temperature (−80 °C) based on the results of the dough system and the solution system. Moreover, for dough leavening performance, the freezing temperature and time should be taken into consideration. The elastic modulus and viscous modulus of the dough decreased after the freezing treatment, while the rheological characteristics of the superchilled samples were close to those of the unfrozen samples, which implies that the superchilling treatment maintained the gluten network structure of the dough.

Mining transcriptomic data to identify Saccharomyces cerevisiae signatures related to improved and repressed ethanol production under fermentation

Saccharomyces cerevisiae is known for its outstanding ability to produce ethanol in industry. Underlying the dynamics of gene expression in S. cerevisiae in response to fermentation could provide informative results, required for the establishment of any ethanol production improvement program. Thus, representing a new approach, this study was conducted to identify the discriminative genes between improved and repressed ethanol production as well as clarifying the molecular responses to this process through mining the transcriptomic data. The significant differential expression probe sets were extracted from available microarray datasets related to yeast fermentation performance. To identify the most effective probe sets contributing to discriminate ethanol content, 11 machine learning algorithms from RapidMiner were employed. Further analysis including pathway enrichment and regulatory analysis were performed on discriminative probe sets. Besides, the decision tree models were constructed, the performance of each model was evaluated and the roots were identified. Based on the results, 171 probe sets were identified by at least 5 attribute weighting algorithms (AWAs) and 17 roots were recognized with 100% performance Some of the top ranked presets were found to be involved in carbohydrate metabolism, oxidative phosphorylation, and ethanol fermentation. Principal component analysis (PCA) and heatmap clustering validated the top-ranked selective probe sets. In addition, the top-ranked genes were validated based on GSE78759 and GSE5185 dataset. From all discriminative probe sets, OLI1 and CYC3 were identified as the roots with the best performance, demonstrated by the most weighting algorithms and linked to top two significant enriched pathways including porphyrin biosynthesis and oxidative phosphorylation. ADH5 and PDA1 were also recognized as differential top-ranked genes that contribute to ethanol production. According to the regulatory clustering analysis, Tup1 has a significant effect on the top-ranked target genes CYC3 and ADH5 genes. This study provides a basic understanding of the S. cerevisiae cell molecular mechanism and responses to two different medium conditions (Mg2+ and Cu2+) during the fermentation process.

Visualizing the next frontiers in wine yeast research.

ABSTRACTA range of game-changing biodigital and biodesign technologies are coming of age all around us, transforming our world in complex ways that are hard to predict. Not a day goes by without news of how data-centric engineering, algorithm-driven modelling, and biocyber technologies—including the convergence of artificial intelligence, machine learning, automated robotics, quantum computing, and genome editing—will change our world. If we are to be better at expecting the unexpected in the world of wine, we need to gain deeper insights into the potential and limitations of these technological developments and advances along with their promise and perils. This article anticipates how these fast-expanding bioinformational and biodesign toolkits might lead to the creation of synthetic organisms and model systems, and ultimately new understandings of biological complexities could be achieved. A total of four future frontiers in wine yeast research are discussed in this article: the construction of fully synthetic yeast genomes, including minimal genomes; supernumerary pan-genome neochromosomes; synthetic metagenomes; and synthetic yeast communities. These four concepts are at varying stages of development with plenty of technological pitfalls to overcome before such model chromosomes, genomes, strains, and yeast communities could illuminate some of the ill-understood aspects of yeast resilience, fermentation performance, flavour biosynthesis, and ecological interactions in vineyard and winery settings. From a winemaker's perspective, some of these ideas might be considered as far-fetched and, as such, tempting to ignore. However, synthetic biologists know that by exploring these futuristic concepts in the laboratory could well forge new research frontiers to deepen our understanding of the complexities of consistently producing fine wines with different fermentation processes from distinctive viticultural terroirs. As the saying goes in the disruptive technology industry, it take years to create an overnight success. The purpose of this article is neither to glorify any of these concepts as a panacea to all ills nor to crucify them as a danger to winemaking traditions. Rather, this article suggests that these proposed research endeavours deserve due consideration because they are likely to cast new light on the genetic blind spots of wine yeasts, and how they interact as communities in vineyards and wineries. Future-focussed research is, of course, designed to be subject to revision as new data and technologies become available. Successful dislodging of old paradigms with transformative innovations will require open-mindedness and pragmatism, not dogmatism—and this can make for a catch-22 situation in an archetypal traditional industry, such as the wine industry, with its rich territorial and socio-cultural connotations.

The Effect of Sound Frequency and Intensity on Yeast Growth, Fermentation Performance and Volatile Composition of Beer.

This study investigated the impact of varying sound conditions (frequency and intensity) on yeast growth, fermentation performance and production of volatile organic compounds (VOCs) in beer. Fermentations were carried out in plastic bags suspended in large water-filled containers fitted with underwater speakers. Ferments were subjected to either 200–800 or 800–2000 Hz at 124 and 140 dB @ 20 µPa. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) was used to identify and measure the relative abundance of the VOCs produced. Sound treatment had significant effects on the number of viable yeast cells in suspension at 10 and 24 h (p < 0.05), with control (silence) samples having the highest cell numbers. For wort gravity, there were significant differences between treatments at 24 and 48 h, with the silence control showing the lowest density before all ferments converged to the same final gravity at 140 h. A total of 33 VOCs were identified in the beer samples, including twelve esters, nine alcohols, three acids, three aldehydes, and six hop-derived compounds. Only the abundance of some alcohols showed any consistent response to the sound treatments. These results show that the application of audible sound via underwater transmission to a beer fermentation elicited limited changes to wort gravity and VOCs during fermentation.

Unraveling continuous 2G ethanol production from xylose using hemicellulose hydrolysate and immobilized superior recombinant yeast in fixed-bed bioreactor

Development of a robust and competitive process for second generation (2G) ethanol production requires efficient fermentation of both glucose and xylose fractions generated after biomass pretreatment and saccharification, using industrial media containing high sugars concentration and inhibitors, under prolonged exposure to high ethanol titers. Thus, it is important to study the influence of these industrial operation conditions on yeast fermentation performance, which has been little addressed in the literature. In this work we evaluated the steady-state stability of continuous 2G ethanol production from xylose in a fixed bed reactor. The bioreactor was packed with recombinant, xylose-utilizing Saccharomyces cerevisiae cells entrapped in calcium alginate and it was operated with different inlet xylose concentrations and dilution rates. Medium supplementation with nutrients and scheduled washing steps were effective in maintaining high xylose conversion levels during continuous fermentation for more than 15 days with an ethanol productivity of 5.0 g/L.h. Effects of prolonged exposure to ethanol and inhibitors present in undetoxified hydrolysate were further investigated in repeated batches. Overall, the results show that improved ethanol tolerance in recombinant yeasts and innovative solutions to increase sugar concentration in the hydrolysates are the main challenges to achieve a feasible industrial process for 2 G ethanol production.

Analysis of fermentative parameters and the importance of Saccharomyces cerevisiae in the development of goods and services

In the fermentation process, yeasts need to adapt to the environmental changes that occur during the production process. Responses to these adjustments can alter biochemical routes and the amount of metabolites produced. Thus, the objective was to analyze the fermentative parameters of industrial yeast strains in different growing conditions, as well as to evaluate the its applicability in different sectors of goods and services. A pre-inoculum was performed with the YPSAC 5% medium for the activation of the yeasts Catanduva-1 and Fleischmann that remained incubated for 24 hours at 30 °C at 250 rpm. After the cells were recovered by centrifugation and inoculated in the fermentation medium based on sugarcane juice at 15 °Brix at temperatures of 30 and 40 °C. Aliquots were removed for the analysis of the fermentative parameters. Concomitantly, a survey was carried out regarding the use of yeasts in the process of preparing goods and services. The data show that the best yeast fermentation performance occurred at 30 °C in 10 hours. In addition, yeasts have the ability to produce, under ideal conditions, metabolites that can be used in different biotechnological processes.

Long-Term Adaption to High Osmotic Stress as a Tool for Improving Enological Characteristics in Industrial Wine Yeast.

Industrial wine yeasts owe their adaptability in constantly changing environments to a long evolutionary history that combines naturally occurring evolutionary events with human-enforced domestication. Among the many stressors associated with winemaking processes that have potentially detrimental impacts on yeast viability, growth, and fermentation performance are hyperosmolarity, high glucose concentrations at the beginning of fermentation, followed by the depletion of nutrients at the end of this process. Therefore, in this study, we subjected three widely used industrial wine yeasts to adaptive laboratory evolution under potassium chloride (KCl)-induced osmotic stress. At the end of the evolutionary experiment, we evaluated the tolerance to high osmotic stress of the evolved strains. All of the analyzed strains improved their fitness under high osmotic stress without worsening their economic characteristics, such as growth rate and viability. The evolved derivatives of two strains also gained the ability to accumulate glycogen, a readily mobilized storage form of glucose conferring enhanced viability and vitality of cells during prolonged nutrient deprivation. Moreover, laboratory-scale fermentation in grape juice showed that some of the KCl-evolved strains significantly enhanced glycerol synthesis and production of resveratrol-enriched wines, which in turn greatly improved the wine sensory profile. Altogether, these findings showed that long-term adaptations to osmotic stress can be an attractive approach to develop industrial yeasts.

The Relationship Between Wort Sugar Concentration and Yeast Carbon Partitioning During Brewing Fermentations

High gravity (HG) and very high gravity (VHG) fermentations are increasingly attractive within the brewing industry as a means of optimizing process efficiency and energy-saving. However, the use of highly concentrated worts is concomitant with a number of biological stress factors that can impact on yeast quality and fermentation performance. In order to eliminate or reduce potentially detrimental effects, brewing yeast respond to their environment by shunting carbon into different metabolic end products, which assist in the protection of cells, but also impact on final ethanol yield. The purpose of this research was to investigate the impact of substrate sugar concentration on carbon partitioning in brewing fermentations. This was conducted using a series of laboratory-scale fermentations with worts of 13°P, 18°P and 24°P, pitched using lager and ale yeast strains. Fermentation performance was assessed with respect to the uptake of wort sugars and the production of key carbon-based metabolites, leading to a calculation of yeast central carbon flux. Analysis of carbon assimilation and dissimilation revealed that changes in intracellular trehalose, glycogen, higher alcohols and esters were observed, however the production of yeast biomass acted as the major trade-off with ethanol production. The data presented here shows for the first time the requirements of yeast populations during HG and VHG conditions and the factors that have a major impact on key performance indicators. This data has major significance for fermentation-based industries globally and is especially important for those sectors seeking to maximize yield from existing resources through high gravity fermentations.

Influence of ammonia and lysine supplementation on yeast growth and fermentation with respect to gluten‐free type brewing using unmalted sorghum grain

SummaryBecause gluten‐free type brewing with unmalted sorghum does not provide adequate nitrogen for complete fermentation, wort supplementation with ammonia (as diammonium phosphate, DAP) or lysine on yeast performance was investigated. By Phenotype Microarray, under aerobic conditions, greater yeast growth was indicated with DAP than lysine both as a single source and combined with sorghum wort amino acids. With sorghum fermentation, both DAP and lysine improved maltose and maltotriose uptake. However, DAP supplementation also maintained yeast numbers (24.0–21.3 × 106 cells mL−1), whereas there was a decline with lysine supplementation. Lysine supplementation also resulted in adverse effects on yeast cell morphology. Neither DAP nor lysine supplementation resulted in evident genetic change to the yeast, but the change in substrate from barley malt wort to unmalted sorghum wort slightly altered the yeast genetically. Therefore, ammonia as DAP has potential as a nitrogen supplement for improving yeast fermentation performance in sorghum gluten‐free brewing.

Serial re-pitching: its effect on yeast physiology, fermentation performance, and product quality

Serial re-pitching is a term given to a practice whereby yeast harvested at the end of fermentation is re-used in subsequent fermentations. The purpose of this paper was to review and summarize existing literatures, research data, and case studies to illustrate the effect of re-pitching on the physiology and fermentation performance of brewing yeast and the resulting quality of beer. Data related to biomarkers used to assess yeast physiology and fermentation performance and quality of beer were compared for various articles. And comparison of the results was done with caution as many of the studies were conducted using different yeast strains, wort gravity, pitching rate, and other fermentation conditions. This study confirms that serial re-pitchings aggravate the effect of pitching rate, wort gravity, cell age, yeast oxygenation, and yeast strain on yeast cell physiology, fermentation performance, and quality of final beer. However, further empirical research at molecular level is crucial.

Effects of Metal Ion Addition on Acetic Acid Removal by Saccharomyces cerevisiae during Lychee Wine Fermentation

Abstract Acetic acid (AA) is the main component of the volatile acidity of lychee wine. It can be generated by yeast, contaminated lactic acid, and AA bacteria at any time during lychee wine fermentation. AA has a negative impact on yeast fermentative performance and affects the quality of lychee wine when present above a given concentration. Thus, excessive amounts of AA should be removed to control the quality of lychee wine. This study investigated the effects of supplementing lychee juice with different concentrations of metal (magnesium, potassium, and calcium) ions on AA removal during lychee wine fermentation at 20 °C. All treatments of metal ion addition negatively affected yeast growth. The addition of either magnesium or potassium ions decreased the AA content, and the lowest values were attained with the addition of 4 mM magnesium ions and 6 mM potassium ions. By contrast, the addition of calcium ions increased the AA content. The addition of metal ions significantly affected metabolites, because more succinic acid, more malic acid, more glycerol, and less acetaldehyde were produced with increasing activities of acetaldehyde dehydrogenase, acetyl-CoA synthetase, isocitrate lyase, and malate synthase. Moreover, the addition of metal ions significantly modified the aroma components of deacidified lychee wine. These findings offer insight into the mechanism of yeast utilization of AA and suggest that selectively adding metal ions may be used a tool to modulate the AA content of lychee wine.

A vertical ball mill as a new reactor design for biomass hydrolysis and fermentation process

A vertical ball mill (VBM) reactor was evaluated for use in biomass conversion processes. The effects of agitation speed (100–200 rpm), number of glass spheres (0–30 units) and temperature (40–46 °C) on enzymatic hydrolysis of rice straw and on glucose fermentation by a thermotolerant Kluyveromyces marxianus strain were separately studied. The results revealed an important role of the spheres during biomass' fiber liquefaction and yeast's fermentative performance. For hydrolysis, the spheres were the only variable with significant positive impact on cellulose conversion, while for fermentation all the variables have influenced the ethanol volumetric productivity (QP). For QP, the spheres showed an interactive effect with temperature, being obtained a maximum of 2.16 g/L.h when both variables were used in the lowest level. By applying the needed adjustments on the levels of the variables for each process (hydrolysis and fermentation), the VBM reactor could be efficiently used for biomass conversion into ethanol.

Application of Plackett-Burman experimental design for investigating the effect of wort amino acids on flavour-active compounds production during lager yeast fermentation

Aroma-active higher alcohols and esters are produced intracellularly in the cytosol by fermenting lager yeast cells, which are of major industrial interest because they determine aroma and taste characteristics of the fermented beer. Wort amino acid composition and their utilization by yeast during brewer's wort fermentation influence both the yeast fermentation performance and the flavour profile of the finished product. To better understand the relationship between the yeast cell and wort amino acid composition, Plackett–Burman screening design was applied to measure the changes in nitrogen composition associated with yeast amino acids uptake and flavour formation during fermentation. Here, using an industrial lager brewing strain of Saccharomyces pastorianus, we investigated the effect of amino acid composition on the accumulation of higher alcohols and volatile esters. The objective of this study was to identify the significant amino acids involved in the flavour production during beer fermentation. Our results showed that even though different flavour substances were produced with different amino acid composition in the fermentation experiments, the discrepancies were not related to the total amount of amino acids in the synthetic medium. The most significant effect on higher alcohol production was exercised by the content of glutamic acid, aromatic amino acids and branch chain amino acids. Leucine, valine, glutamic acid, phenylalanine, serine and lysine were identified as important determinants for the formation of esters. The future applications of this information could drastically improve the current regime of selecting malt and adjunct or their formula with desired amino acids in wort. Copyright © 2017 The Institute of Brewing & Distilling

Comparative transcriptomic analysis reveals similarities and dissimilarities in Saccharomyces cerevisiae wine strains response to nitrogen availability.

Nitrogen levels in grape-juices are of major importance in winemaking ensuring adequate yeast growth and fermentation performance. Here we used a comparative transcriptome analysis to uncover wine yeasts responses to nitrogen availability during fermentation. Gene expression was assessed in three genetically and phenotypically divergent commercial wine strains (CEG, VL1 and QA23), under low (67 mg/L) and high nitrogen (670 mg/L) regimes, at three time points during fermentation (12h, 24h and 96h). Two-way ANOVA analysis of each fermentation condition led to the identification of genes whose expression was dependent on strain, fermentation stage and on the interaction of both factors. The high fermenter yeast strain QA23 was more clearly distinct from the other two strains, by differential expression of genes involved in flocculation, mitochondrial functions, energy generation and protein folding and stabilization. For all strains, higher transcriptional variability due to fermentation stage was seen in the high nitrogen fermentations. A positive correlation between maximum fermentation rate and the expression of genes involved in stress response was observed. The finding of common genes correlated with both fermentation activity and nitrogen up-take underlies the role of nitrogen on yeast fermentative fitness. The comparative analysis of genes differentially expressed between both fermentation conditions at 12h, where the main difference was the level of nitrogen available, showed the highest variability amongst strains revealing strain-specific responses. Nevertheless, we were able to identify a small set of genes whose expression profiles can quantitatively assess the common response of the yeast strains to varying nitrogen conditions. The use of three contrasting yeast strains in gene expression analysis prompts the identification of more reliable, accurate and reproducible biomarkers that will facilitate the diagnosis of deficiency of this nutrient in the grape-musts and the development of strategies to optimize yeast performance in industrial fermentations.

Preliminary Evidence of Inositol Supplementation Effect on Cell Growth, Viability and Plasma Membrane Fluidity of the Yeast Saccharomyces Cerevisiae

Inositol is known to initiate positive effects on yeast fermentation performance, cell growth and tolerance against environmental stresses, especially high ethanol concentration. The precise mechanisms by which inositol improves such parameters are yet to be elucidated. The present study was performed to investigate the effect of inositol supplementation on growth, fermentation performance and plasma membrane fluidity during normal gravity fermentation. Yeast cells were grown in a chemically defined fermentation medium with 15% (w/v) glucose, lacking inositol and with 0.1 or 0.4g/L inositol supplementation. Cell density, cell viability, glucose consumption and ethanol production were monitored for 96hours. Plasma membrane fluidity was monitored at 24hours fermentation, representing the respiro-fermentative growth phase, by measuring generalized polarization (GP) of laurdan. The effect of ethanol on membrane fluidity also monitored by measuring GP after exposing cell to 18% (v/v) ethanol. The results of the present experiment indicated that although inositol supplementation did not seem to improve fermentation performance as assessed by glucose consumption and ethanol production, it did improve cell growth leading to higher cell densities. While inositol-supplemented cells had higher growth rates and cell density, they had significantly lower viability, thus the viable cell counts were similar with and without supplementation. There is also evidence that inositol supplementation leads to increased membrane fluidity with significantly lower GP values for yeast cells grown in the inositol supplemented media. However when exposed to high ethanol concentrations, inositol-supplemented yeasts showed a greater GP decrease than those grown without inositol. Thus, interestingly, the non- supplemented yeasts with lower baseline membrane fluidity seemed to better withstand the fluidizing effects of ethanol. We are in the process of confirming the viability of ethanol-treated cells as well as furthering the investigations on inositol effects on stress tolerance and other physiological parameters.

The Brewing Process: Optimizing the Fermentation

Beer is a carbonated alcoholic beverage obtained by alcoholic fermentation of malt wort boiled with hops. Brown beer obtained at Beer Pilot Station of University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca was the result of a recipe based on blond, caramel and black malt in different proportions, water, hops and yeast. This study aimed to monitorize the evolution of wort in primary and secondary alcoholic fermentation in order to optimize the process. Two wort batches were assambled in order to increase the brewing yeast fermentation performance. The primary fermentation was 14 days, followed by another 14 days of secondary fermentation (maturation). The must fermentation monitoring was done by the automatic FermentoStar analyzer. The whole fermentation process was monitorized (temperature, pH, alcohol concentration, apparent and total wort extract).