Yeast ratio is a critical factor for sequential fermentation of papaya wine by Williopsis saturnus and Saccharomyces cerevisiae

Increase the Content of Ester Compounds in Blueberry Wine Fermentation with the Ester-Producing Yeast: Candida glabrata, Pichia anomala, and Wickerhamomyces anomalus

The co-fermentation of Saccharomyces cerevisiae and ester-producing yeasts is considered to be an effective way to improve the flavor and quality of fruit wine. In this study, three kinds of ester-producing yeasts (Candida glabrata NCUF308.1, Pichia anomala NCUF306.1, and Wickerhamomyces anomalus NCUF307.1) and S. cerevisiae NCUF309.2 were used to simulate blueberry wine co-fermentation at different ratios. The results showed that, compared with S. cerevisiae NCUF309.2 fermentation (S), the population of S. cerevisiae NCUF309.2 in co-fermentation samples decreased to varying degrees, and the content of ethanol also decreased. The results also showed that the co-fermentation of C. glabrata NCUF308.1 and S. cerevisiae NCUF309.2 at the ratio of 1:1 (CS1), co-fermentation of P. anomala NCUF306.1 and S. cerevisiae NCUF309.2 at the ratio of 5:1 (PS5), and co-fermentation of W. anomalus NCUF307.1 and S. cerevisiae NCUF309.2 at the ratio of 5:1 (WS5) could significantly increase the content of ester compounds (p < 0.05), which was 3.29, 4.75, and 3.04 times that of the S sample, respectively. Among them, the sample of CS1 was characterized by phenethyl acetate and isoamyl acetate, while the samples of CS5 and PS5 were characterized by propyl octanoate and ethyl decanoate, and the sample of WS5 was characterized by 3-methylbutyl hexanoate. However, the contents of odor active compounds were higher in the CS1 sample. Therefore, the samples of CS1 had the potential to create the distinctive flavor of blueberry wine.

Production of Coffee Cherry Spirits from Coffea arabica Varieties

Coffee pulp, obtained from wet coffee processing, is the major by-product accumulating in the coffee producing countries. One of the many approaches valorising this underestimated agricultural residue is the production of distillates. This research project deals with the production of spirits from coffee pulp using three different Coffea arabica varieties as a substrate. Coffee pulp was fermented for 72 h with a selected yeast strain (Saccharomyces cerevisiae L.), acid, pectin lyase, and water. Several parameters, such as temperature, pH, sugar concentration and alcoholic strength were measured to monitor the fermentation process. Subsequently, the alcoholic mashes were double distilled with stainless steel pot stills and a sensory evaluation of the products was conducted. Furthermore, the chemical composition of fermented mashes and produced distillates were evaluated. It showed that elevated methanol concentrations (>1.3 g/L) were present in mashes and products of all three varieties. The sensory evaluation found the major aroma descriptor for the coffee pulp spirits as being stone fruit. The fermentation and distillation experiments revealed that coffee pulp can be successfully used as a raw material for the production of fruit spirits. However, the spirit quality and its flavour characteristics can be improved with optimised process parameters and distillation equipment.

Fine tuning of medium chain fatty acids levels increases fruity ester production during alcoholic fermentation

Pichia fermentans Z9Y-3 and its intracellular enzymes were inoculated along with S. cerevisiae in synthetic grape must to modulate fruity ester production. The levels of ester-related enzymes, ester precursors, and fruity esters were monitored every 24 h during fermentation. Results showed that the levels of ethyl acetate, acetate higher alcohol esters (AHEs), short chain fatty acid ethyl esters (SFEs), and medium chain fatty acid ethyl esters (MFEs) were significantly enhanced in mixed fermentation. Pearson correlation analysis further revealed that higher alcohols and fatty acids played a more important role in fruity ester production than enzymes; Particularly, the correlation coefficient between fatty acids and MFEs was 0.940. In addition, supplementation of medium chain fatty acids (7.2 mg/L) at the metaphase of single S. cerevisiae fermentation improved ethyl acetate, AHE, SFE, and MFE production by 42.56%, 21.00%, 61.33%, and 90.04%, respectively, although the high level of ethyl acetate might result in off-flavors.

Investigating the Effect of Selected Non-Saccharomyces Species on Wine Ecosystem Function and Major Volatiles

Natural alcoholic fermentation is initiated by a diverse population of several non-Saccharomyces yeast species. However, most of the species progressively die off, leaving only a few strongly fermentative species, mainly Saccharomyces cerevisiae. The relative performance of each yeast species is dependent on its fermentation capacity, initial cell density, ecological interactions as well as tolerance to environmental factors. However, the fundamental rules underlying the working of the wine ecosystem are not fully understood. Here we use variation in cell density as a tool to evaluate the impact of individual non-Saccharomyces wine yeast species on fermentation kinetics and population dynamics of a multi-species yeast consortium in synthetic grape juice fermentation. Furthermore, the impact of individual species on aromatic properties of wine was investigated, using Gas Chromatography-Flame Ionization Detector. Fermentation kinetics was affected by the inoculation treatment. The results show that some non-Saccharomyces species support or inhibit the growth of other non-Saccharomyces species in the multi-species consortium. Overall, the fermentation inoculated with a high cell density of Starmerella bacillaris displayed the fastest fermentation kinetics while fermentation inoculated with Hanseniaspora vineae showed the slowest kinetics. The production of major volatiles was strongly affected by the treatments, and the aromatic signature could in some cases be linked to specific non-Saccharomyces species. In particular, Wickerhamomyces anomalus at high cell density contributed to elevated levels of 2-Phenylethan-1-ol whereas Starm. bacillaris at high cell density resulted in the high production of 2-methylpropanoic acid and 3-Hydroxybutanone. The data revealed possible direct and indirect influences of individual non-Saccharomyces species within a complex consortium, on wine chemical composition.