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With the sustained popularity of hazy IPAs, brewers have explored multiple approaches to maximizing stable haze that will remain in suspension throughout the shelf life of the beer. Our recent investigations into yeast-dependent haze have uncovered specific brewing yeast strains that promote the formation of haze in heavily dry-hopped beer styles. These brewing strains have been termed "haze-positive" and furthermore, the timing of dry hop additions has been found to be another key factor in producing this stable haze. Classical genetics have identified YIL169C (herein referred to as HZY1) as both necessary and sufficient for the haze-positive phenotype in the yeast strain most widely used for Hazy IPAs. HZY1 encodes a candidate glycoprotein and our recent findings suggest it is localized to the cell wall through a GPI anchor. Surprisingly, using long-read sequencing data we uncovered extensive genetic variation in HZY1 across brewing strains. The haze-positive phenotype correlates with an expansion in the N-terminal serine-rich region. We propose that the Hzy1 glycoprotein is a critical component to yeast-dependent colloidal haze and the genetic variation in this locus contributes the range of haze phenotypes observed across industrial brewing strains. [ABSTRACT FROM AUTHOR]

Metabolic dysregulation leading to sugar-phosphate accumulation is toxic in organisms ranging from bacteria to humans. By comparing two models of sugar-phosphate toxicity in Saccharomyces cerevisiae, we demonstrate that toxicity occurs, at least in part, through multiple, isomer-specific mechanisms, rather than a single general mechanism.

Chemical preservatives are ubiquitously used to suppress the growth of or kill microorganisms across numerous industries, including the food industry. Utilizing yeast functional genomic techniques, genes and their functions can be observed at a genomic scale to elucidate how environmental stressors (e.g., chemical preservatives) impact microbial survival. These types of chemical genomics approaches can reveal genetic mutations that result in preservative resistance or sensitivity, assist in identification of preservative mechanism of action, and can be used to compare different preservatives for rational design of preservative mixtures. In this proof‐of‐concept study, we performed deletion and high‐copy genetic expression screens to identify mutants that confer drug resistance to sodium benzoate, potassium sorbate, rosemary extract, and Natamax. By observing overlapping mutant genes between genetic screens, we were able to identify functional overlap between chemical preservatives and begin to explain mechanisms of action for these compounds. [ABSTRACT FROM AUTHOR]

Auxotrophic strains starving for their cognate nutrient, termed auxotrophic starvation, are characterized by a shorter lifespan, higher glucose wasting phenotype, and inability to accomplish cell cycle arrest when compared to a "natural starvation," where a cell is starving for natural environmental growth‐limiting nutrients such as phosphate. Since evidence of this physiological response is limited to only a subset of auxotrophs, we evaluated a panel of auxotrophic mutants to determine whether these responses are characteristic of a broader range of amino acid auxotrophs. Based on the starvation survival kinetics, the panel of strains was grouped into three categories—short‐lived strains, strains with survival similar to a prototrophic wild type strain, and long‐lived strains. Among the short‐lived strains, we observed that the tyrosine, asparagine, threonine, and aspartic acid auxotrophs rapidly decline in viability, with all strains unable to arrest cell cycle progression. The three basic amino acid auxotrophs had a survival similar to a prototrophic strain starving in minimal media. The leucine, tryptophan, methionine, and cysteine auxotrophs displayed the longest lifespan. We also demonstrate how the phenomenon of glucose wasting is limited to only a subset of the tested auxotrophs, namely the asparagine, leucine, and lysine auxotrophs. Furthermore, we observed pleiotropic phenotypes associated with a subgroup of auxotrophs, highlighting the importance of considering unintended phenotypic effects when using auxotrophic strains especially in chronological aging experiments. Take‐away: Amino acid auxotrophs under auxotrophic starvation display variable survival rates.Glucose wasting is limited to a subset of amino acid auxotrophs.Some amino acid auxotrophs display pleiotropic effects. [ABSTRACT FROM AUTHOR]

Fermentation is a critical step in the production of coffee when following standard wet processing, one of the most common methods used to remove the mucilage layer from coffee cherries. During this step, the de-pulped coffee cherries undergo fermentation with native yeast that modifies the flavor profile of the resultant coffee. This study aimed to ferment green coffee beans using commercial yeast strains from beer and wine prized for their ability to produce specific flavors, and subsequently evaluate the aroma and flavor of the coffee using coffee consumers. Four Saccharomyces cerevisiae strains were used: Belgian Ale, Sourvisiae, 71 B, and Tropical IPA, along with one non-Saccharomyces, Toluraspora delbrueckii (Biodiva), and a non-inoculated control sample. The green coffee beans underwent a controlled wet fermentation for 72 h, followed by roasting, grinding, and brewing. Results showed that flavor profiles varied broadly by yeast strain, suggesting that producing novel flavors in coffee through fermentation is feasible and that these flavors survive the roasting process; however, higher liking scores were still reported for the control sample compared to the fermented samples. Biodiva, a strain used in wine to produce esters and fruity flavors, resulted in coffee with highly fruity notes, and all strains were rated more floral than the control, while the sample fermented with Sourvisiae yeast used in the brewing of sour ales resulted in coffee that was both perceived as more sour and had the lowest pH, likely due to the degree of lactic acid this strain is engineered to produce. Further, there were significant color differences between the samples. In conclusion, fermenting green coffee beans with brewing and winemaking yeast strains strongly impacted the flavor and aroma of the resultant coffee; however, evaluating larger panels of strains or optimizing strain performance may yield flavor profiles more suitable for coffee. [ABSTRACT FROM AUTHOR]

Wine and alcoholic apple cider are commonly back-sweetened with unpasteurized juice to produce fresh, natural, and palatable sweetened alcoholic beverages. Foodborne pathogens may be introduced from unpasteurized juice into alcoholic beverages through this back-sweetening process. Although foodborne pathogens generally do not survive under low pH conditions or a high alcohol environment, the die-off of these pathogens has not been established to ensure the microbiological safety of the products. To establish the holding conditions that would provide the required 5-log pathogen reduction requirements for these back-sweetened beverages, we evaluated the survival of three common foodborne pathogens, E. coli O157:H7, Salmonella enterica, and Listeria monocytogenes, in modified white grape juice and apple juice models. White grape juice and apple juice were modified with hydrochloric acid and sodium hydroxide and with ethanol to achieve conditions that are similar to back-sweetened white wine and alcoholic apple cider in regard to pH and ethanol content. Foodborne pathogen cocktails were inoculated separately into modified juice models, and their survival in the juice models was recorded over a 96-h period. Our results show that a combination of low pH and high ethanol content resulted in faster pathogen die-off compared with higher pH and lower ethanol conditions. The holding times required for different combinations of pH and ethanol concentration for each juice model to achieve a 5-log reduction were reported. This research provides data to validate pathogen die-off to comply with juice hazard analysis and critical control point 5-log pathogen inactivation requirements for backsweetened wine and alcoholic apple cider. [ABSTRACT FROM AUTHOR]

Diastatic yeasts are a major contamination risk to packaged beer. Brewery quality control programs rely on selective microbial growth media and molecular detection of the STA1 gene; however, there is a wide functional range of diastatic activity that remains unresolved by these current methods. Herein, a comprehensive analysis of diastatic yeast selection media using our collection of STA1+ strains is provided. For the preparation of microbial selection media, several factors to control including plate age, autoclave cycling conditions, cupric sulfate, and dipotassium phosphate concentrations are highlighted. Further several functional assays that confirm the variation in diastatic activity across STA1+ strains and show a clear correlation with earlier onset and increasing strength in strains that contain an intact STA1 promoter are presented. Furthermore, a robust and simple plate-based assay to confirm diastatic activity of potential contaminants has been developed. Collectively, these functional assays provide improved risk assessment of re-fermentation in packaged product with the potential for determining contaminant thresholds for different STA1+ strains and weighing in on the decision to destroy beer or issue a product recall. [ABSTRACT FROM AUTHOR]