Yeast Starter Cultures Research Articles

Improving the Taste of Robusta Coffee by Fermentation with Yeast Inoculum and Its Effect on Caffeine Content

Harvesting coffee process by farmers generally executed entirety, resulting rainbow harvest. Coffee fermentation with yeast starter cultures Saccharomyces cerevisiae Y612, Candida parapsilosis Y207 and Torulospora delbrueckii Y594 was executed separately to determine the role of starter cultures on caffeine and robusta coffee taste at different maturity levels. The study was conducted at the Indonesian Industrial and Beverage Crops Research Institute in Sukabumi,, from June to November 2022. The experiment used a factorial complete randomized design. The first factor was the maturity level of the coffee and starter culture as the second factor. Fermentation was implemented for 48 hours inoculated with 108 cells/mL starter culture. The results showed that the temperature fluctuated, the pH value always decreased to 4.50 and T. delbrueckii was the starter culture with the highest activity during fermentation. Inoculum-fermented robusta coffee caffeine content was higher than non-inoculum. The lowest caffeine content was found in spontaneously fermented red fruit of 1.39%, while the highest caffeine content was produced by red fruit samples inoculated with C. parapsilosis of 2.7%. Robusta coffee with S. cerevisiae inoculation brought the best taste of robusta coffee with 82.10%, there was no significant difference between the red harvest coffee fruit and the fermented rainbow color with a starter culture. Keywords: Caffeine, Harvest, Inoculation, Maturity level, Starter cultures

Yeast Starter Culture Identification to Produce of Red Wines with Enhanced Antioxidant Content.

Grape variety, quality, geographic origins and phytopathology can influence the amount of polyphenols that accumulate in grape tissues. Polyphenols in wine not only shape their organoleptic characteristics but also significantly contribute to the positive impact that this beverage has on human health. However, during the winemaking process, the total polyphenol content is substantially reduced due to the adsorption onto yeast wall polymers and subsequent lees separation. Despite this, limited information is available regarding the influence of the yeast starter strain on the polyphenolic profile of wine. To address this issue, a population consisting of 136 Saccharomyces cerevisiae strains was analyzed to identify those with a diminished ability to adsorb polyphenols. Firstly, the reduction in concentration of polyphenolic compounds associated to each strain was studied by assaying Total Phenolic Content (TPC) and Trolox Equivalent Antioxidant Capacity (TEAC) in the wines produced by micro-scale must fermentation. A total of 29 strains exhibiting a TPC and TEAC reduction ≤ 50%, when compared to that detected in the utilized grape must were identified and the nine most-promising strains were further validated by larger-scale vinification. Physico-chemical analyses of the resulting wines led to the identification of four strains, namely ITEM6920, ITEM9500, ITEM9507 and ITEM9508 which showed, compared to the control wine, a TPC and TEAC reduction ≤ 20 in the produced wines. They were denoted by a significant (p < 0.05) increased amount of anthocyanin, quercetin and trans-coutaric acid, minimal volatile acidity (<0.2 g/L), absence of undesirable metabolites and a well-balanced volatile profile. As far as we know, this investigation represents the first clonal selection of yeast strains aimed at the identifying "functional" fermentation starters, thereby enabling the production of regional wines with enriched polyphenolic content.

Selecting autochthonous lactic acid bacteria for co-inoculation in Chinese bayberry wine production: Stress response, starter cultures application and volatilomic study

This study focused on isolating and characterising autochthonous lactic acid bacteria (LAB) from spontaneously fermented Chinese bayberry (CB) and their potential application in CB wine fermentation in co-inoculation with yeast starter cultures. Numerous LAB, including Lactiplantibacillus (Lp.) plantarum (9), Limosilactobacillus (Lb.) fermentum (6), Lactococcus (Lc.) lactis (3), Enterococcus (Ec.) hirae (1), Leuconostoc (Le.) mesenteroides (1), and Weissella (Ws.) cibaria (1), were isolated and identified. The isolated strains Lp. plantarum ZFM710 and ZFM715, together with Lb. fermentum ZFM720 and ZFM722, adapted well to unfavourable fermentation environment, including ethanol, osmolality, and acidity stresses, were selected for producing CB wine by co-inoculation with Saccharomyces cerevisiae. During fermentation, the presence of LAB promoted the development of S. cerevisiae, while the population dynamics of LAB in different groups at different stages showed strain-specific differences. Fermentation trials involving LAB yielded a lower ethanol concentration except for Lp. plantarum ZFM715. Compared to the pure S. cerevisiae fermented sample, the addition of LAB led to a clear modulation in organic acid composition. Lb. fermentum strains in co-fermentation led to significant decreases in each classified group of aroma compounds, while Lp. plantarum ZFM715 significantly increased the complexity and intensity of aroma compounds, as well as the intensities of fruity and floral notes. The study selects interesting strains for the design of starter cultures for use in CB wine production, underlining the interest in the selection of autochthonous LAB in fruit wines, with the aim of improving the adaptation of bacteria to specific environmental conditions and shaping the unique traits of the finished products.

Effect of Solar Pre-Drying and Yeast Starter Inoculation Treatments on the Chemical Composition of Cocoa (Theobroma cacao L.) Beans from Southwestern Colombia.

In Southwestern Colombia, cocoa clones are cultivated in which productivity characteristics predominate over bean quality. In this study, cocoa beans of the CCN-51 clone harvested in the Tumaco region (Nariño, Colombia) were fermented following four different treatments: (1) spontaneously (at room temperature for 120 h) in traditional conditions (Control); (2) traditional processing with a pre-drying (sun-dried for 24 h) treatment (PD); (3) with fermentation (for 120 h) after inoculation of a yeast starter culture (YS); and (4) including both treatments, pre-drying and yeast inoculation (PD + YS). Chemical composition, fatty acids, total polyphenol, methylxanthines (theobromine and caffeine) and lactic acid content of cocoa beans were determined. Chemical and fatty acid composition and theobromine content were not affected by the different fermentation treatments applied (p > 0.05). When analyzing total polyphenol content, YS (16.62 mg/g) and PD + YS (17.74) treatments significantly decreased (p < 0.05) the content of these compounds at the end of the fermentation process, affecting cocoa flavour, while PD treatment decreased (p < 0.05) the caffeine content (0.68 mg/g) of cocoa beans. Finally, lactic acid content decreased because of both inoculation of yeast starter (1.11 mg/g) and mainly the pre-drying treatment (0.60). In conclusion, solar pre-drying in the open air and the inoculation of yeast starter treatments could improve the final quality of cocoa beans.

Species identification and strain discrimination of fermentation yeasts Saccharomyces cerevisiae and Saccharomyces uvarum using Raman spectroscopy and convolutional neural networks.

The use of S. cerevisiae and S. uvarum yeast starter cultures is a common practice in the alcoholic beverage fermentation industry. As yeast strains from different or the same species have variable fermentation properties, rapid and reliable typing of yeast strains plays an important role in the final quality of the product. In this study, Raman spectroscopy combined with CNN achieved accurate identification of S. cerevisiae and S. uvarum isolates at both the species and strain levels in a rapid, non-destructive, and easy-to-operate manner. This approach can be utilized to test the identity of commercialized dry yeast products and to monitor the diversity of yeast strains during fermentation. It provides great benefits as a high-throughput screening method for agri-food and the alcoholic beverage fermentation industry. This proposed method has the potential to be a powerful tool to discriminate S. cerevisiae and S. uvarum strains in taxonomic, ecological studies and fermentation applications.

Continuous automated microbial monitoring in laboratory-scale winemaking experiments

The management of microbial flora is a key element of the winemaking process. It impacts process time, fermentation quality (e.g., production of alcohol, development of aroma compounds, absence of undesirable microorganisms) and the overall quality of the final wine product. In microbial flora management, real-time microbial monitoring is crucial. When applying currently used classical methods (e.g., cultivation on plates) or more recent technologies (e.g., flow cytometry), the flora sampling frequency is not optimal and taking around-the-clock measurements involves high labour costs. The objective of this study was to evaluate the feasibility of automated microbial monitoring based on an online flow cytometry system for different laboratory-scale applications in the field of winemaking. Initially, a protocol for automated sampling, double-staining and analysis was validated on yeast and bacterial populations after rehydration of the starter cultures. The system was then tested on a variety of increasingly complex biological systems, simulating its applications in the winemaking process. First, a yeast starter culture preparation for “prise de mousse” was tested. Then, a mixed-culture alcoholic fermentation was monitored. Finally, a microbial-focused observation of wine aging was emulated. By overcoming specific constraints linked to the must medium (e.g., sugars, alcohol contents, production of gas, fermentation duration), the results show the potential of this technology for (1) automated yeast or bacterial monitoring in a wide range of laboratory-scale wine environments, (2) simultaneous monitoring of both total and intact populations of multiple microorganisms, (3) long observation periods, and (4) high sampling frequencies for high-resolution data. It could be particularly useful for facilitating and improving control of potential contaminants or stuck fermentations, as well as better piloting starter preparations, alcoholic fermentations, or malolactic fermentations.

Unlocking the Aromatic Potential of Native Coffee Yeasts: From Isolation to a Biovolatile Platform.

Postharvest processing of coffee has been shown to impact cup quality. Yeasts are known to modulate the sensory traits of the final cup of coffee after controlled fermentation at the farm. Here, we enumerated native coffee yeasts in a Nicaraguan farm during dry and semidry postharvest processing of Arabica and Robusta beans. Subsequently, 90 endogenous yeast strains were selected from the collected endogenous isolates, identified, and subjected to high-throughput fermentation and biovolatile generation in a model system mimicking postharvesting conditions. Untargeted volatile analysis by SPME-GC-MS enabled the identification of key aroma compounds generated by the yeast pool and demonstrated differences among strains. Several genera, including Pichia, Candida, and Hanseniaspora, showed both strain- and species-level variability in volatile generation and profiles. This fermentation platform and biovolatile database could represent a versatile opportunity to accelerate the development of yeast starter cultures for generating specific and desired sensory attributes in the final cup of coffee.

Isolation, Identification and Determination of Saccharomyces cerevisiae Yeast Species from The Wines Made by Spontaneous Fermentation Using Papazkarası Grapes from Thrace Region

Especially in large-scale commercial wine production, fermentation is usually carried out by using the species of Saccharomyces cerevisiae yeast cultures. Standard wine yeast starter cultures are brought from abroad and used in industrial winemaking in our country. Thus, in course of time, the wines of all producers began to show similar properties. Today, studies focus on terroir wines production with local characteristics by using the countries' own local wine yeasts as a starter. Within the scope of this study Papazkarası grapes were collected from 4 vineyards with different characteristics, such as viticulture practices, microclimatic conditions and locations in the borders of Edirne and Kırklareli. In addition, the grapes were also collected from the vineyard in Tekirdağ Viticulture Research Institute. Spontaneous fermentation was done by crushing the collected grapes in the laboratory. At the end of the fermentation, yeast isolations were made from the musts to YPD medium and a total of 66 isolates were obtained as a result of purification. Fermentation rate, H2S production amount, growth at high temperature, growth at high sugar concentration, resistance to high ethanol, ability to grow at low pH values, resistance to SO2, and volatile acid analysis were done to determine whether they meet the technological requirements for basic winemaking, together with two commercial wine yeasts. DNA sequencing analyzes were made by selecting 15 of the isolates that were found to have the necessary characteristics and it was determined that they belonged to the Saccharomyces cerevisiae species. DNA fingerprinting analysis was performed using delta 12-21 primers to determine the strain differences of the isolates determined to belong to the same species. By DNA fingerprint analysis, it was determined that 9 out of 15 isolates were different strains.

Carbohydrate Sources Influence the Microbiota and Flavour Profile of a Lupine-Based Moromi Fermentation.

Lupine-based seasoning sauce is produced similarly to soy sauces and therefore generates a comparable microbiota and aroma profile. While the koji state is dominated by Aspergillus oryzae, the microbiome of the moromi differs to soy moromi, especially in yeast composition due to the absence of Zygosaccharomyces rouxii and Debaryomyces hansenii as the dominant yeast. In this study, we monitored the addition of a carbohydrate source on the microbiome and aroma profile of the resulting sauce. Compared to previous studies, the usage of a yeast starter culture resulted in a sparsely diverse microbiota that was dominated by D. hansenii and T. halophilus. This led to a pH below 5 even after four months of incubation and most of the measured aroma compounds were pyrazines and acids. The addition of wheat and buckwheat resulted in a temporary change in the yeast consortium with the appearance of Z. rouxii and additional bacterial genera. The aroma profile differs in the presence of pyrazines and esters. Since no significant differences in the taste and odour of wheat-added and buckwheat-added sauce was sensed, both substrates influence the lupine sauce in a similar way.

THE USEFULNESS OF FERMENTED KOMBUCHA TEA FOR THE PRODUCTION OF LOW-ALCOHOLIC DRINKS

Background. Consumers' growing interest in fermented food contributes to the development of the market in functional drinks, which are rich in biologically active compounds that positively affect the human body. One of such drinks is the fermented Kombucha tea, appreciated for its taste and beneficial health properties. The study aimed to select suitable yeast starter culture for the production of fermented low-alcohol beverages based on Kombucha having good microbiological and sensory quality and high antioxidant activity. The scope of the research included developing a technological process for the Kombucha tea drink with the addition of wine, brewing and probiotic yeast, and subsequently, determining the quality of the designed drinks. The research methodology included the analysis of pH value, alcohol content, microbiological analysis, antioxidant activity, total polyphenol content and a sensory analysis. Result and conclusion. Based on the research conducted, it was found that obtaining low-alcohol fermented beverages based on Kombucha is possible, and the quality of these products depended on the yeast starter cultures. They significantly impacted all the tested parameters of the final products. The lowalcohol drinks obtained were characterized by a low level of alcohol and a high content of antioxidant compounds, as well as the desired microbiological and sensory quality. The results obtained are a pilot for further research into the usefulness of fermented Kombucha tea for the production of low-alcohol beverages.

Interactions among Relevant Non-Saccharomyces, Saccharomyces, and Lactic Acid Bacteria Species of the Wine Microbial Consortium: Towards Advances in Antagonistic Phenomena and Biocontrol Potential

The topic of microbial interactions is of notable relevance in oenology, being connected with their impact on microbial biodiversity and wine quality. The interactions among different couples of microorganisms, in particular yeasts and lactic acid bacteria representative of the must/wine microbial consortium, have been tested in this study. This interaction’s screening has been implemented by means of plate assays, using culture medium, grape juice, and wine agar as substrates. Different antagonistic phenomena have been detected, belonging to the following interaction categories: yeast-yeast, yeast-bacteria, bacteria-yeast, and bacteria-bacteria. In general, the inhibitory activity has been observed in all three media agar used as substrates, resulting in more frequent on culture medium, followed by grape juice and, finally, wine. Specifically, the work is one of the first reports demonstrating the reciprocal interactions between non-Saccharomyces yeasts (NSY) and malolactic bacteria. The findings shed new light on the co-inoculation of the yeast starter culture with malolactic bacteria, as well as the biocontrol potential of Lactic Acid Bacteria (LAB) strains. Highlighted microbial interactions are relevant for the management of alcoholic fermentation, malolactic fermentation, and the development of distinctive aroma profiles, control of spoilage yeasts, and the selection of tailored mixed starter cultures. In addition, the plate assay method could be a fast, cheap, and suitable method to exclude negative interactions among Saccharomyces spp., NSY, and malolactic bacteria during trials from regional spontaneous fermentations with the aim to select tailored mixed starter cultures.

Effects of Saccharomyces cerevisiae and Starmerella bacillaris on the physicochemical and sensory characteristics of sparkling pear cider (Perry)

This study was aimed to produce pear cider (Perry), using small caliber pears cv Abate Fètel, fermented by Starmerella bacillaris and Saccharomyces cerevisiae in co-inoculated (COF) and sequential (SEF) mixed cultures in comparison with S. cerevisiae monoculture fermentation (AXF), evaluating the influence of yeast starter cultures on Perry characteristics. The perries were re-fermented in bottle by S. cerevisiae strain EC1118. During primary fermentation, growth and fermentation kinetics were different in the co-inoculated and sequential fermentations in comparison with pure S. cerevisiae fermentation; however, sugars were depleted, and 6% (v/v) ethanol was produced in all the trials. Glycerol content was significantly higher in mixed fermentations due to Starm. bacillaris metabolism (+ 20% in COF, and + 42% in SEF conditions). After re-fermentation in bottle, higher levels of 3-Methyl-1-butanol, 1-propanol, acetaldehyde and esters were detected in Perry from the mixed fermentations. All the Perries were accepted by the consumers (general liking values from 6.01 to 6.26). Perries’ appearance from mixed fermentations was described as less intense and more clear. The use of small caliber pears cv Abate Fètel and Starm. bacillaris in combination with S. cerevisiae in Perry production might be a suitable tool to obtain novel beverages with distinctive organoleptic features.

Functional yeast starter cultures for cocoa fermentation.

SummaryThe quest to develop a performant starter culture mixture to be applied in cocoa fermentation processes started in the 20th century, aiming at achieving high‐quality, reproducible chocolates with improved organoleptic properties. Since then, different yeasts have been proposed as candidate starter cultures, as this microbial group plays a key role during fermentation of the cocoa pulp‐bean mass. Yeast starter culture‐initiated fermentation trials have been performed worldwide through the equatorial zone and the effects of yeast inoculation have been analysed as a function of the cocoa variety (Forastero, Trinitario and hybrids) and fermentation method (farm‐, small‐ and micro‐scale) through the application of physicochemical, microbiological and chemical techniques. A thorough screening of candidate yeast starter culture strains is sometimes done to obtain the best performing strains to steer the cocoa fermentation process and/or to enhance specific features, such as pectinolysis, ethanol production, citrate assimilation and flavour production. Besides their effects during cocoa fermentation, a significant influence of the starter culture mixture applied is often found on the cocoa liquors and/or chocolates produced thereof. Thus, starter culture‐initiated cocoa fermentation processes constitute a suitable strategy to elaborate improved flavourful chocolate products.

Effect of Commercial Yeast Starter Cultures on Cabernet Sauvignon Wine Aroma Compounds and Microbiota.

Commercial Saccharomyces cerevisiae plays an important role in the traditional winemaking industry. In this study, the correlation of microbial community and aroma compound in the process of alcohol fermentation of Cabernet Sauvignon by four different commercial starters was investigated. The results showed that there was no significant difference in the fermentation parameters of the four starters, but there were differences in microbial diversity among the different starters. The wine samples fermented by CEC01 had higher microbial abundance. GC-MS detected a total of 58 aromatic compounds from the fermentation process by the experimental yeasts. There were 25 compounds in the F6d variant, which was higher than in other samples. The PCA score plot showed that 796 and F15 yeast-fermented wines had similar aromatic characteristic compositions. According to partial least squares (PLS, VIP > 1.0) analysis and Spearman’s correlation analysis, 11, 8, 8 and 10 microbial genera were identified as core microorganisms in the fermentation of 796, CEC01, CECA and F15 starter, respectively. Among them, Leuconostoc, Lactobacillus, Sphingomonas and Pseudomonas played an important role in the formation of aroma compounds such as Ethyl caprylate, Ethyl caprate and Ethyl-9-decenoate. These results can help us to have a better understanding of the effects of microorganisms on wine aroma and provide a theoretical basis for improving the flavor quality of Cabernet Sauvignon wine.

Glutathione production by non-Saccharomyces yeasts and its impact on winemaking: A review

Glutathione (GSH) is a non-protein thiol naturally present in grape berries and produced by yeasts during fermentation. It has a strong antioxidant activity; thus, the addition of pure GSH during winemaking is recommended to limit the oxidative phenomena of wine, preserving sensory characteristics and stability, ultimately promoting a healthier product by reducing the need for SO2 addition. A promising alternative approach considers the use of yeast starter cultures high producers of this compound in situ, during the fermentation process, in substitution of external GSH addition. Recent research showed that multistarter fermentations with non-Saccharomyces yeasts produce even higher concentrations of GSH compared to single Saccharomyces cerevisiae. Accumulation of GSH in yeast cells is also considered valuable during the growth and dehydration of biomass for starter production, aiding strains to overcome the stressful conditions of industrial process. Moreover, a current trend in oenology is the use during fermentation of inactivated dry yeasts preparations as a source of nutrients, and many of them contain GSH-enriched cells. The aim of this review was to assess the significance of GSH production for the exploitation of wine-related non-Saccharomyces yeasts, both in starter biomass production and during fermentations, which were until now studied in detail for S. cerevisiae. This compendium highlights an interesting new feature of non-conventional yeasts and upgrade the strategy of multistarter fermentation as a valuable tool to positively modulate wine composition.

Machine Learning Techniques Disclose the Combined Effect of Fermentation Conditions on Yeast Mixed-Culture Dynamics and Wine Quality.

The use of yeast starter cultures consisting of a blend of Saccharomyces cerevisiae and non-Saccharomyces yeasts has increased in recent years as a mean to address consumers’ demands for diversified wines. However, this strategy is currently limited by the lack of a comprehensive knowledge regarding the factors that determine the balance between the yeast-yeast interactions and their responses triggered in complex environments. Our previous studies demonstrated that the strain Hanseniaspora guilliermondii UTAD222 has potential to be used as an adjunct of S. cerevisiae in the wine industry due to its positive impact on the fruity and floral character of wines. To rationalize the use of this yeast consortium, this study aims to understand the influence of production factors such as sugar and nitrogen levels, fermentation temperature, and the level of co-inoculation of H. guilliermondii UTAD222 in shaping fermentation and wine composition. For that purpose, a Central Composite experimental Design was applied to investigate the combined effects of the four factors on fermentation parameters and metabolites produced. The patterns of variation of the response variables were analyzed using machine learning methods, to describe their clustered behavior and model the evolution of each cluster depending on the experimental conditions. The innovative data analysis methodology adopted goes beyond the traditional univariate approach, being able to incorporate the modularity, heterogeneity, and hierarchy inherent to metabolic systems. In this line, this study provides preliminary data and insights, enabling the development of innovative strategies to increase the aromatic and fermentative potential of H. guilliermondii UTAD222 by modulating temperature and the availability of nitrogen and/or sugars in the medium. Furthermore, the strategy followed gathered knowledge to guide the rational development of mixed blends that can be used to obtain a particular wine style, as a function of fermentation conditions.

Ecology and population dynamics of yeast starter cultures in cocoa beans fermentation.

This study aimed to investigate controlled fermentation of cocoa beans with selected yeasts as starter cultures via integrating microbiological, biochemical, and chromatographic analyses. The steps involved in the yeast starter culture test were of the following order: 1) counting, isolation, purification, and biochemical identification of yeasts, 2) selection of ethanol-producing yeasts, 3) selection of thermotolerant yeasts, and 4) evaluation of physicochemical parameters of the selected yeasts in controlled fermentation of cocoa (F1 - Saccharomyces ssp. and Hanseniaspora ssp. and F2 - spontaneous fermentation - control). A total of 32 yeasts were isolated from three sampling points (M1, M2, and M3), which comprised 50% Candida ssp., 9.4% Rhodotorula ssp., 18.8% Saccharomyces ssp., and 18.8% Hanseniaspora ssp. The yeasts identified as Saccharomyces ssp. (n = 6) were subjected to the ethanol production test. Saccharomyces spp. CLV09 showed the highest concentration of ethanol in the simulated cocoa medium (3.5% v/v). Hanseniaspora spp. CVL20 and CVL19 strains showed the highest thermotolerance at 42°C after 72 h of growth. The starter cultures with Saccharomyces ssp. and Hanseniaspora ssp. showed a similar growth rate of the mesophilic aerobic population in both F1 and F2. Fermentation of the starter culture showed a higher production of organic acids than spontaneous fermentation (F2). Thus, Saccharomyces ssp. and Hanseniaspora ssp. can be used as a starter culture in cocoa fermentation.

Physicochemical properties, antioxidant content, volatile organic compounds and sensory profile of cocoa beans fermented with yeast starter cultures

This study determined the influence of selected yeast starters on the antioxidant content, volatile organic compounds and sensory qualities of fermented cocoa beans. Cocoa beans fermented with Hanseniaspora thailandica (MH979675), Pichia kudriazevii (MH979681), or a mixture of both species in fermentation (20 kg) were highly reproducible based on the physicochemical parameters (temperature, pH of nibs, fermentation index and cut test). The usage of H. thailandica improved the total polyphenols content of cocoa beans with fermentation index around 1.24 and 1.33. The correlation analyses suggested that phenolics and flavonoids compounds may not be the main constituents that led to the antioxidant activities of the fermented samples. Principal Component Analysis showed distinct differences in VOC profiles between spontaneous and fermentation using yeast. Sweet and spicy notes were only found in sample fermented with yeast. The inoculation of yeast in fermentation influenced the sensorial and antioxidant properties of cocoa beans.

Selection of Indigenous Saccharomyces cerevisiae Strains and Exploitation of a Pilot-Plant to Produce Fresh Yeast Starter Cultures in a Winery

The inoculation of grape juice with Saccharomyces cerevisiae strains selected from indigenous yeast populations can be a suitable tool to control alcoholic fermentation, contributing to producing wines with typical flavor and aroma and, hence, the demand for native starter cultures is increasing. However, since low amounts of indigenous yeast biomasses are usually required for local winemaking, the industrial production of these yeasts can be expensive. Therefore, in this study, after selecting an indigenous S. cerevisiae strain based on relevant oenological and technological features, a pilot-plant for easy and rapid production of fresh yeast biomass directly in a winery located in Tuscany, was exploited. The selected yeast strain was used as a starter to carry out 25 and 100 hL fermentations and its enological performance was compared with that of the commercial starter normally used in the winery. Chemical and sensory analysis of the resulting wines showed that they differentiated according to the used yeast strain, with the wines produced by the indigenous S. cerevisiae strain being characterized by a distinctive aromatic and sensory profile. In conclusion, the pilot-plant effectively resulted in producing fresh yeast starter cultures in the winery to be successfully used to carry out alcoholic fermentations.

An indigenous &lt;I&gt;Saccharomyces cerevisiae&lt;/I&gt; yeast strain isolated from Paarl regional Shiraz grapes to enhance Shiraz wine typicity

Wine yeast starter cultures differ in their ability to release aroma-enhancing metabolites associated with typical varietal wines. Therefore, this study investigated an indigenous Saccharomyces cerevisiae isolated from Paarl regional Shiraz grapes for the release of, amongst others, volatile thiols (aroma compounds traditionally associated with white cultivars, especially Sauvignon blanc) during the 2016 and 2017 vintages using Shiraz grape must. Chemical analyses of final wines showed that the indigenous strain i.e., NI6 produced Shiraz wines lower volatile acidity (VA) and acetic acid concentrations than wines produced with reference strains i.e., WE372 and MERIT, respectively. This was further supported by descriptive sensory evaluations of wines, as NI6 wines had typical Shiraz varietal aromas and flavours, i.e.,“berry”, “jammy”, “smoky” and “spicy and peppery”. This yeast strain also produced wines with more 3-mercapto-1-hexanol (3MH), a volatile thiol that imparts black currant aromas in red wines, than both red wine reference strains in 2016. Both red wine reference strains, however, produced red wines with higher ester compounds (imparts “fruity” aroma) concentrations than strain NI6. Nonetheless, the ability of NI6 to consistently release volatile thiols during both vintages is advantageous for Shiraz wine typicity. Overall, this study showed that wines with a positive correlation with black and/or fruits aromas and flavours also had volatile thiol levels above its sensory detection thresholds, which indicates that ester compounds are not solely responsible for Shiraz wine fruity aromas and flavours as was traditionally reported.