Effect of additives on the rehydration of Saccharomyces cerevisiae wine strains in active dry form: influence on viability and performance in the early fermentation phase

The effect of five additives on the rehydration process of three commercial Saccharomyces cerevisiae wine strains, in the form of active dry yeast, was tested using the approach of design of experiments. The response to additives was monitored by observing the viability, measured using fluorescence methodology at the end of the rehydration experiments, and fermentative performance, focusing attention on the first phase of fermentation, assessed based on ethanol production and the total number of cells after 48 h from the time of inoculation in synthetic must. The results showed a correlation between viability and the presence of magnesium in the rehydration medium. However, improvement in viability was not associated with better fermentation performance, which was not affected or in some cases significantly reduced. Among the additives examined, only rehydration with inactive dry yeast and ammonium showed a positive effect on the subsequent fermentations, but not for all of the strains tested. In general, considering all of the additives tested, no relationship was found between viability at the end of rehydration and fermentation performance. These findings suggest that the viability of the rehydrated yeast cells may not be a good index of fitness in the subsequent fermentation. Copyright © 2014 The Institute of Brewing & Distilling     

Rehydration of active dried yeast: impact on strength and stiffness of yeast cells measured using microelectromechanical systems

This study investigated the rehydration of active dried yeast and the impact of temperature and wort density on the strength and stiffness of individual cells using a microelectromechanical system. Dried yeast was rehydrated using a variety of methods, including direct pitching into wort (13.6°P) at 12, 22 and 30°C, as well as propagation using YEPD media (4.2°P). Cell viability was found to broadly correlate with measurement of cell strength and stiffness. Both wort density and temperature affected viability and physical characteristics of the cells after 1 h of rehydration. Yeast cells rehydrated at low temperature and high wort density burst at a lower force (0.26 ± 0.02 μN) than cells rehydrated using high temperature and low density media (0.50 ± 0.10 μN). Cells rehydrated at higher temperatures or using low density media showed no significant difference in strength and stiffness when compared with high viability, actively fermenting yeast. Changes in yeast physiology, owing to stress responses, may contribute to the observed differences in mechanical properties. These findings have application in brewery design, as pumping, centrifugation, storage and associated shear impart mechanical stress upon yeast cells. © 2018 The Institute of Brewing & Distilling     

Rehydration of Active Dry Brewing Yeast and its Effect on Cell Viability

The use of active dry yeast (ADY) in the brewing industry is becoming increasingly attractive due to several key features, including its capacity to be stored conveniently and to be prepared rapidly for use. However, some studies have reported that undesirable effects may occur when employing lager strains in the ADY form, such as abnormal flocculation, haze formation and a less stable foam structure. These effects have been linked to reduced viability, caused by cell death during the drying and rehydration processes. It is known that the means by which yeast is rehydrated is important to maintain membrane integrity and to prevent potentially lethal damage from occurring. In order to determine the impact of rehydration conditions on yeast viability, three industrially manufactured ADY strains were examined. Each strain was rehydrated using a variety of parameters and monitored for cell viability using slide culture and a variety of brightfield and fluorescent stains.     

Viability, efficacy, and storage stability of freeze-dried biocontrol agent Candida sake using different protective and rehydration media

Viability, efficacy against Penicillium expansum on Golden Delicious apples, and storage stability of freeze-dried Candida sake strain CPA-1 were studied. The effect of several protective agents and rehydration media was investigated in the freeze drying of C. sake. Skimmed milk at 10% concentration was a good rehydration medium for all protectants tested. In general, good viability results were obtained when the same solution was used as a protectant and as a rehydration medium. The best survival was obtained when C. sake cells were protected with 10% lactose + 10% skimmed milk and rehydrated with skimmed milk (85% viability). The potential for biocontrol of the best freeze-dried treatments against P. expansum on apples was compared with that of fresh cells. Freeze-dried treatments at 1 x 10(7) CFU/ml reduced the incidence of decay by 45 to 66%. The best biocontrol effect was obtained with cells that had been freeze dried using 10% lactose + 10% skimmed milk as a protectant and 1% peptone as a rehydration medium, with a 66% reduction in rot incidence. However, in all treatments, the efficacy of freeze-dried cells was significantly lower than fresh cells. The stability of freeze-dried samples decreased during storage and was influenced by storage temperature. In the best treatment, storage of C. sake cells for 60 days at 4 degrees C resulte in final concentrations of 2.5 x 10(8) CFU/ml, which was a 10-fold reduction in relation to the initial starting concentration of cells prior to freeze drying.     

Vitamins in wine: Which,what for,and how much?

Vitamins are essential compounds to yeasts, and notably in winemaking contexts. Vitamins are involved in numerous yeast metabolic pathways, including those of amino acids, fatty acids, and alcohols, which suggests their notable implication in fermentation courses, as well as in the development of aromatic compounds in wines. Although they are major components in the course of those microbial processes, their significance and impact have not been extensively studied in the context of winemaking and wine products, as most of the studies focusing on the subject in the past decades have relied on relatively insensitive and imprecise analytical methods. Therefore, this review provides an extensive overview of the current knowledge regarding the impacts of vitamins on grape must fermentations, wine-related yeast metabolisms, and requirements, as well as on the profile of wine sensory characteristics. We also highlight the methodologies and techniques developed over time to perform vitamin analysis in wines, and assess the importance of precisely defining the role played by vitamins in winemaking processes, to ensure finer control of the fermentation courses and product characteristics in a highly complex matrix.     

Rapid Assessment of Yeast Viability and Yeast Vitality During Alcoholic Fermentation

A flow cytometric method based on the measurement of the efflux percentage of carboxyfluorescein after staining of yeast cells with carboxyfluorescein diacetate is reported. This efflux percentage was followed throughout alcoholic fermentations performed with various pH and temperature conditions. The results obtained show that the efflux percentage is a good indicator of the energetic state of yeast cells and varies through the fermentation in a similar manner to the specific ethanol production rate. These results suggest that this flow cytometric method can be applied to assess viability and to predict vitality of yeast cells in alcoholic fermentations.     

葡萄酒活性干酵母的研究 Ⅰ.葡萄酒活性干酵母的生产和应用

以2株葡萄酒酵母1450(Saccharomyces cerevisiae)和Am_(-1)(saccharomyces bayanus)为试验菌株,进行了活性干酵母的培养和干燥等工艺条件的研究。对活性干酵母在酿酒中的应用技术也进行了研究。试验结果表明,活性干酵母的制备工艺是可行的。活性干酵母1450和Am_(-1)适用于酿制干型葡萄酒和其它果酒。与野生酵母的自然发酵结果相比,干酵母发酵平稳彻底,发酵时间较短,发酵结束时,干酵母的沉淀较好,原酒含残糖量和挥发酸量低,酿制的酒质量和风味较好。     

Differential synthesis of fermentative aroma compounds of two related commercial wine yeast strains

The specific impact of the yeast strain on the wine flavour and aroma has not been well characterised yet because this effect is usually combined with other variables during the winemaking. In this study, the contribution to wine flavour of two Saccharomyces cerevisiae strains widely used in wine production, VIN13 and EC1118, was evaluated after fermentation at 15 °C. Chemical defined grape juice media fermented with the EC1118 strain showed higher solvent, fatty and pineapple aroma attributes, while that fermented with the VIN13 strain exhibited higher banana, fruity, yeasty and green attributes. Sensorial and chemical analyses evidenced that the production of flavour-active compounds is significantly affected by the yeast strain, as well as by the temperature of fermentation, as shown by comparing the former data with those from fermentations carried out at 28 °C under identical culture conditions.     

The enumeration and identification of acetic acid bacteria from South African red wine fermentations

Acetic acid bacteria are microorganisms that can profoundly influence the quality of wine. Surprisingly, little research has been done on these microorganisms in the winemaking field. The object of this study was to investigate the occurrence of acetic acid bacteria in South African red wine fermentations and to identify the dominant species occurring. Acetic acid bacteria were isolated and enumerated from small-scale and commercial red must fermentations in 1998 and 1999, respectively. The initial occurrence of acetic acid bacteria in the must was shown to vary with cell numbers ranging from 10(6)-10(7) to 10(4)-10(5) cfu/ml for the 1998 and 1999 musts, respectively. The acetic acid bacteria decreased to 10(2)-10(3) cfu/ml in musts having a low pH (< or = 3.6), whereas in some musts having a high pH (> or = 3.7), the cell numbers increased during fermentation. During the process of cold soaking, the cell numbers of acetic acid bacteria also increased until inoculation with commercial wine yeast. Gluconobacter oxydans dominated in the fresh must and Acetobacter pasteurianus and A. liquefaciens during fermentation. This study showed that A. liquefaciens and A. hansenii were present in significant numbers, which has not been reported before.     

Biogenic amines and the importance of starter cultures for malolactic fermentation

Biogenic amines are compounds produced mainly by microorganisms from the decarboxylation of some amino acids which may cause several health issues in susceptible people. In the winemaking process, one of the factors with the greatest impact on the final concentration of biogenic amines in wine is the malolactic fermentation, which mainly involves the action of lactic acid bacteria. This article gathers scientific literature on the importance of the use of inoculation in winemaking, especially for the potential formation of biogenic amines in spontaneous fermentations, with emphasis on malolactic fermentation. It establishes the set of attributes that influence the formation of biogenic amines in winemaking and aspects related to their toxicity, especially histamine and tyramine. With the growing interest of the market in products with less chemical appeal, the safety of wines, whether from non‐conventional or traditional winemaking, must increasingly be observed. Therefore, the importance of using cultivated starter cultures is discussed, along with the safety of organic wines and the presentation of articles that seek to reconcile the production of organic wine with the preservation of the ‘microbiological terroir’ in a safe way, using selected wild yeasts and lactic acid bacteria.     

复水温度对香菇复水特性及品质的影响

香菇是中国产量最高和市场消费量最大的食用菌。干制是香菇的主要加工方式,而干香菇需复水后才能作为原料被烹调或进一步加工。本研究将热风干燥的香菇分别在25,45,65℃和85℃下复水,研究香菇复水过程中复水比、外观、质构和风味品质的变化。结果表明,在45℃复水270 min,干香菇吸水后表面的褶皱较为舒展,微观结构显示其菌丝恢复膨胀且伸展。同时,其复水比稳定保持在3.88,剪切力(1 290.28 g)、弹力(0.66 g)和复原力(0.34 g)适中,咀嚼性(656.02 g)最大,说明香菇复水完全且质地柔软适中,易被切开。此外,45℃复水香菇所含特征含硫化合物的含量较高,以1,2,3,5,6-五硫杂环庚烷(67.02%)和1,2,4-三硫环戊烷(39.06%)为主,风味较浓郁。综上,复水温度显著影响香菇复水后的食用品质,将干香菇在45℃复水270 min可获得品质较好的复水香菇。     

Phenolic profile of blackberry wine produced using Korean winemaking techniques in earthenware jars

This research evaluated the winemaking potential of ‘Natchez’ and ‘Triple Crown’ blackberries grown in Oklahoma and examined the phenolic composition of blackberry wines made using modified Korean traditional winemaking techniques. The winemaking variables were fermentation temperature (21.6 vs 26.6°C), and fermentation type (yeast inoculation vs wild fermentation). High‐performance liquid chromatography was used to examine the phenolic compounds in blackberry juice and wine. The phenolic compounds consisted of anthocyanins (kuromanin, keracyanidin, delphinidin) and phenolic acids (gallic acid, catechin, caffeic acid, epicatechin, p‐coumaric acid). The ‘Natchez’ berries had higher concentrations of anthocyanins (kuromanin) while ‘Triple Crown’ berries had higher levels of phenolic acids (p‐coumaric acid). For many compounds, a higher fermentation temperature generally corresponded to higher concentrations of the phenolic compound in the wine after three months aging, but this was not universally observed. Accordingly, fermentation temperature may best be matched with individual cultivars via experimentation in order to maximise extraction and retention of phenolic compounds in the finished wines. Overall, the Korean traditional winemaking technique may be a good technique to add value to wines made from blackberries suited for production in a mid‐continental climate such as the central USA. © 2018 The Institute of Brewing & Distilling     

Effect of freeze drying and protectants on viability of the biocontrol yeast Candida sake

The effects of freezing method, freeze drying process, and the use of protective agents on the viability of the biocontrol yeast Candida sake were studied. Freezing at -20 degrees C was the best method to preserve the viability of C. sake cells after freeze drying using 10% skim milk as a protectant (28.9% survival). Liquid nitrogen freezing caused the highest level of damage to the cells with viability < 10%. Different concentrations of exogenous substances including sugars, polyols, polymers and nitrogen compounds were tested either alone or in combination with skim milk. There was little or no effect when additives were used at 1% concentration. Galactose, raffinose and sodium glutamate at 10% were the best protective agents tested alone but the viability of freeze-dried C. sake cells was always < 20%. Survival of yeast cells was increased from 0.2% to 30-40% by using appropriate protective media containing combinations of skim milk and other protectants such as 5% or 10% lactose or glucose, and 10% fructose or sucrose.     

Increased flavour diversity of Chardonnay wines by spontaneous fermentation and co-fermentation with Hanseniaspora vineae

Discovery, characterisation and use of novel yeast strains for winemaking is increasingly regarded as a way for improving quality and to provide variation, including subtle characteristic differences in fine wines. The objective of this work was to evaluate the use of a native apiculate strain, selected from grapes, Hanseniaspora vineae (H. vineae) 02/5A. Fermentations were done in triplicate, working with 225 L oak barrels, using a Chardonnay grape must. Three yeast fermentation strategies were compared: conventional inoculation with a commercial Saccharomyces cerevisiae strain, ALG 804, sequential inoculation with H. vineae and then strain ALG 804 and spontaneous fermentation. Yeast strain identification was performed during fermentation, in which the apiculate strain was found to be active, until 9% of alcohol in volume, for the co-fermentation and the spontaneous fermentation was completed by three native S. cerevisiae strains. Basic winemaking parameters and some key chemical analysis, such as concentration of glycerol, biogenic amines, organic acids, and aroma compounds were analysed. Sensory analysis was done using a trained panel and further evaluated with professional winemakers. Sequential inoculation with H. vineae followed by S. cerevisiae resulted in relatively dry wines, with increased aroma and flavour diversity compared with wines resulting from inoculation with S. cerevisiae alone. Wines produced from sequential inoculations were considered, by a winemaker’s panel, to have an increased palate length and body. Characteristics of wines derived from sequential inoculation could be explained due to significant increases in glycerol and acetyl and ethyl ester flavour compounds and relative decreases in alcohols and fatty acids. Aroma sensory analysis of wine character and flavour, attributed to winemaking using H. vineae, indicated a significant increase in fruit intensity described as banana, pear, apple, citric fruits and guava. GC analysis of the relative accumulation of 23 compounds to significantly different concentrations for the three fermentation strategies is discussed in relation to aroma compound composition.     

Effect of oenological practices on microbial populations using culture-independent techniques

Sulphur dioxide (SO(2)) addition and yeast inoculation are well-established practices in winemaking for restricting the growth of indigenous yeasts and bacterial populations. The effect of these oenological practices on wine microbial populations has been evaluated using culture-independent methods. These are quantitative PCR (qPCR) for the enumeration of yeasts, lactic acid bacteria (LAB) and acetic acid bacteria (AAB), and PCR-DGGE to determine the yeast and bacteria species diversity. The PCR-DGGE method detected a low yeast and bacteria species diversity. On the contrary, the specificity of the primers designed for the qPCR allowed that minor microbial groups such as Hanseniaspora were accurately quantified regardless of a large presence of other microbial groups such as Saccharomyces. From an oenological point of view, inoculation increased the proportion of Saccharomyces vs. non-Saccharomyces in a shorter time. Hanseniaspora increased during the first phase and decreased during the latter phases of the process, especially in the sulphited fermentations. Both yeast inoculation and SO(2) kept the LAB populations at very low level, while the AAB populations were hardly affected by these two practices.     

A Dynamic Analysis of Higher Alcohol and Ester Release During Winemaking Fermentations

Isobutanol, isoamyl acetate and ethyl hexanoate production during winemaking fermentations was precisely described. Volatile compound concentrations and their rates of change and losses in the exhausted gas were determined throughout the fermentation. Negligible amounts of isobutanol were lost, whatever the fermentation temperature. In contrast, 56 % of the ethyl hexanoate and 34 % of the isoamyl acetate were stripped by CO₂ when the temperature profile simulated red winemaking conditions. Even at a moderate temperature of 20 °C, typical of white wine fermentations, 40 % of the ethyl hexanoate and 21 % of the isoamyl acetate were lost. The effect of temperature on the production of the volatile compounds was assessed by running fermentations at different temperatures, with the same medium and strain. By taking into account the volatile compound losses in the exhausted gas, changes in volatile compound production were found to be smaller than those usually calculated from the concentrations in the wine. These findings highlight the potential importance of knowledge concerning aroma gas–liquid balances for both an understanding of yeast metabolism and the identification of innovative control strategies minimizing aroma losses.     

Determination of microwave drying and rehydration kinetics of green peppers with the bioactive and textural properties

The aim of this study was to determine the effect of microwaves on drying and rehydration kinetics of green pepper varieties (sweet, green, and bell) and the bioactive and textural properties of dried and rehydrated peppers. Drying was performed at 90, 180, and 90 + 180 W and dried peppers were rehydrated at 25, 50, and 70°C. The best drying fits were obtained using the equations of both Sigmoid and Hii et al. for drying, and two term exponential decay was the most appropriate model for rehydration. The lowest and highest final rehydration ratio values were obtained for the peppers dried at 180 and 90 W, respectively at each temperature and pepper variety. Among peppers, bell pepper showed the lowest color change (ΔE) and it was the most potent to recover initial color in rehydration. Peppers had softer texture in both drying and rehydration treatment. Total phenolic content of peppers was reduced around 56–65% compared to the fresh pepper by drying and this decrement was reached up to 87% in rehydrated peppers. Results showed that drying at 180 W and rehydration at 70°C provided faster drying and rehydration as well maintained the quality characteristics of green peppers.     

Growth of non-Saccharomyces yeasts affects nutrient availability for Saccharomyces cerevisiae during wine fermentation

Yeast produces numerous secondary metabolites during fermentation that impact final wine quality. Although it is widely recognized that growth of diverse non-Saccharomyces (NS) yeast can positively affect flavor complexity during Saccharomyces cerevisiae wine fermentation, the inability to control spontaneous or co-fermentation processes by NS yeast has restricted their use in winemaking. We selected two NS yeasts from our Uruguayan native collection to study NS-S. cerevisiae interactions during wine fermentation. The selected strains of Hanseniaspora vineae and Metschnikowia pulcherrima had different yeast assimilable nitrogen consumption profiles and had different effects on S. cerevisiae fermentation and growth kinetics. Studies in which we varied inoculum size and using either simultaneous or sequential inoculation of NS yeast and S. cerevisiae suggested that competition for nutrients had a significant effect on fermentation kinetics. Sluggish fermentations were more pronounced when S. cerevisiae was inoculated 24h after the initial stage of fermentation with a NS strain compared to co-inoculation. Monitoring strain populations using differential WL nutrient agar medium and fermentation kinetics of mixed cultures allowed for a better understanding of strain interactions and nutrient addition effects. Limitation of nutrient availability for S. cerevisiae was shown to result in stuck fermentations as well as to reduce sensory desirability of the resulting wine. Addition of diammonium phosphate (DAP) and a vitamin mix to a defined medium allowed for a comparison of nutrient competition between strains. Addition of DAP and the vitamin mix was most effective in preventing stuck fermentations.     

Evaluating the Influence of Malolactic Fermentation Inoculation Practices and Ageing on Lees on Biogenic Amine Production in Wine

Biogenic amines are compounds, produced primarily by lactic acid bacteria (LAB) that negatively affect the wholesomeness of wine. Standard winemaking practices can greatly influence the levels of biogenic amines in wine. The aim of this study was to determine the relative contribution of different malolactic fermentation (MLF) practices and ageing of wines on fermentation lees to the final levels of biogenic amines. Wines were made on small scale over two harvest seasons with two red grape cultivars. Treatments included spontaneous MLF, co-inoculated MLF, MLF inoculated after alcoholic fermentation (conventional inoculation) and 4 months of ageing in the presence and absence of fermentation lees of all MLF treatments. Biogenic amine concentrations were measured by high-performance liquid chromatography at key winemaking stages and statistically analysed for the effects of MLF treatment and winemaking stage. Results indicate that the presence of indigenous LAB increased the risk of biogenic amine formation. Inoculation proved to reduce biogenic amine production over time compared to spontaneous MLF and co-inoculation even more than conventional inoculation. The presence of yeast lees during ageing generally led to higher final concentrations of biogenic amines in wines than the absence of lees. This study confirms other works that conclude that spontaneous MLF and uncontrolled ageing on yeast lees are generally unpredictable and pose a risk of biogenic amine contamination in finished wines.