Brewer's Yeast Research Articles

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Hydrolyzed proteins are used as attractive agents in McPhail traps for monitoring of fruit flies (Tephritidae). There has been no defined role for monitoring of insects belonging to the Lonchaeidae family. Currently, there is a great concern in using most efficient and low-cost attractive materials. Thus, this study aimed at assessing the attractiveness of solid and liquid baits in capturing of frugivorous flies (Tephritidae and Lonchaeidae). Therefore, we carried out four trials in coffee plantations (Coffea arabica L.) during two different periods (May/ 2013 and July/ 2014). A randomized block design with four treatments and five replications was used in the first period, and ten treatments with four replications the following year. Two distinct experiments were carried out, one using baits in solid and another in liquid form, which consisted of applying 10 g for trap (solid) or 200 mL solution of the same compounds diluted in water (5%: p/ v). In 2013, we tested yeast extract with and without sugar, brewer's yeast, citrus pulp and hydrolyzed protein as control. In 2014, five additional baits were tested: acai, plum and grape flours, passion fruit fiber and poultry feces. In all experiments, a 5% hydrolyzed protein solution was used as control. Eight days after being set, traps were assessed. Even the yeast extract, with and without sugar, and the brewer's yeast, in solid form, were as attractive as control treatment in capturing flies. The poultry feces and yeast extract, with and without sugar in solution form, can be used to replace hydrolyzed protein in capturing tephritids. Lonchaeids are barely attracted by the hydrolyzed protein. Additionally, yeast extract and poultry feces can be used for monitoring and biodiversity studies of the Lonchaeidae fauna. Key words: Fruit growing, monitoring, trap, protein.

Genomics: History of brewer's yeast revealed.

Genomics: History of brewer's yeast revealed.

Degradation of spent craft brewer's yeast by caprine rumen hyper ammonia-producing bacteria.

Spent yeast from craft beers often includes more hops (Humulus lupulus L.) secondary metabolites than traditional recipes. These compounds include α-and β- acids, which are antimicrobial to the rumen hyper ammonia-producing bacteria (HAB) that are major contributors to amino acid degradation. The objective was to determine if the hops acids in spent craft brewer's yeast (CY; ~ 3·5mgg(-1) hops acids) would protect it from degradation by caprine rumen bacteria and HAB when compared to a baker's yeast (BY; no hops acids). Cell suspensions were prepared by harvesting rumen fluid from fistulated goats, straining and differential centrifugation. The cells were re-suspended in media with BY or CY. After 24h (39°C), HAB were enumerated and ammonia was measured. Fewer HAB and less ammonia was produced from CY than from BY. Pure culture experiments were conducted with Peptostreptococcus anaerobiusBG1 (caprine HAB). Ammonia production by BG1 from BY was greater than from CY. Ammonia production was greater when exogenous amino acids were included, but similar inhibition was observed in CY treatments. These results indicate that rumen micro-organisms deaminated the amino acids in CY to a lesser degree than BY. Spent brewer's yeast has long been included in ruminant diets as a protein supplement. However, modern craft beers often include more hops (Humulus lupulus L.) than traditional recipes. These compounds include α- and β- acids, which are antimicrobial to the rumen hyper ammonia-producing bacteria (HAB) that are major contributors to amino acid degradation. This study demonstrated that hops acids in spent craft brewer's yeast protected protein from destruction by HABinvitro. These results suggest that the spent yeast from craft breweries, a source of beneficial hops secondary metabolites, could have value as rumen-protected protein.

Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae.

Lignocellulosic bioethanol from renewable feedstocks using Saccharomyces cerevisiae is a promising alternative to fossil fuels owing to environmental challenges. S. cerevisiae is frequently challenged by bacterial contamination and a combination of lignocellulosic inhibitors formed during the pre-treatment, in terms of growth, ethanol yield and productivity. We investigated the phenotypic robustness of a brewing yeast strain TMB3500 and its ability to adapt to low pH thereby preventing bacterial contamination along with lignocellulosic inhibitors by short-term adaptation and adaptive lab evolution (ALE). The short-term adaptation strategy was used to investigate the inherent ability of strain TMB3500 to activate a robust phenotype involving pre-culturing yeast cells in defined medium with lignocellulosic inhibitors at pH 5.0 until late exponential phase prior to inoculating them in defined media with the same inhibitor cocktail at pH 3.7. Adapted cells were able to grow aerobically, ferment anaerobically (glucose exhaustion by 19 ± 5 h to yield 0.45 ± 0.01 g ethanol g glucose−1) and portray significant detoxification of inhibitors at pH 3.7, when compared to non-adapted cells. ALE was performed to investigate whether a stable strain could be developed to grow and ferment at low pH with lignocellulosic inhibitors in a continuous suspension culture. Though a robust population was obtained after 3600 h with an ability to grow and ferment at pH 3.7 with inhibitors, inhibitor robustness was not stable as indicated by the characterisation of the evolved culture possibly due to phenotypic plasticity. With further research, this short-term adaptation and low pH strategy could be successfully applied in lignocellulosic ethanol plants to prevent bacterial contamination.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0234-8) contains supplementary material, which is available to authorized users.

Spent brewer's yeast extract as an ingredient in cooked hams

This work describes the effect of the incorporation of 1% spent yeast extract into cooked hams. Physical/chemical/sensorial characteristics and changes during 12 and 90days storage were evaluated on control and treated cooked hams processed for 1.5, 2.0, 2.5 or 3h. Spent yeast extract addition increased hardness, chewiness, ash, protein and free amino acid content. Similar volatile profiles were obtained, although there were some quantitative differences. No advantages were observed for increased cooking time.No significant differences were observed for physical and sensorial parameters of cooked hams with spent yeast extract at 12 and 90days post production, but His, aldehydes and esters increased at the end of storage. This behaviour was similar to that observed for control hams.The higher hardness of cooked ham with 1% yeast extract was due to the stronger gel formed during cooking and was maintained during storage. This additive acts as gel stabilizer for cooked ham production and could potentially improve other processing characteristics.

Growth and feed utilization of goldfish (Carassius auratus) fed graded levels of brewers yeast (Saccharomyces cerevisiae)

In this study, a feeding trial was conducted to examine the potential of replacing fish meal with brewers yeast in practical diet of goldfish (Carassius auratus). Five isoproteic (37% CP) and isocaloric (3350 kcal/kg) diets were formulated to contain graded levels of brewers yeast. Fish meal protein was replaced by 0%, 15%, 25%, 35%, and 45% of yeast. Each diet was randomly allocated to triplicate groups of 20 fish (initial average weight of 0.56 g fish-1) in glass aquarium (65L). Fish were fed three times per day to apparent satiation for 84 days. At the end of the experiment, weight gain, specific growth rate (SGR), feed conversion ratio (FCR), protein efficiency ratio (PER), condition factor (CF), survival rate (SR), hepatosomatic indices (HSI) and body composition of goldfish fry were determined. According to the results, weight gain, SGR, FCR and PER of fish fed the diet including yeast replaced 35% of the fish meal were better than those of fish fed the other diets. There were no significant differences in SR and HSI values among fish fed diets (p >0.05). However, CF among fish fed the experimental diets was significantly differ (p >0.05). Whole body composition was similar among fish fed different diets. The optimal replacement level of fishmeal protein by brewers yeast was determined by second-order polynomial regression to be (y= 2, 2237- 0,0004x2 + 0,0279x; R² = 0,9977) 34.875%, on the basis of SGR

Biomass-derived porous heteroatom-doped carbon spheres as a high-performance catalyst for the oxygen reduction reaction

A high-performance, spherical, heteroatom-doped carbon catalyst for the oxygen reduction reaction (ORR), with a porous structure and a high surface area, has been prepared through a hydrothermal treatment process and subsequent carbonization procedures using brewer's yeast powder, ferric chloride, and ammonium hydroxide as precursors. We found that the addition of iron had a significant effect on the catalyst's spherical morphology and ORR activity. Electrochemical measurements demonstrated that the catalyst has excellent ORR performance, with a half-wave potential 28 mV more positive (0.861 V vs. RHE) than that of commercial 20 wt.% Pt/C (0.833 V vs. RHE) in an alkaline medium. The catalyst also displays remarkable methanol tolerance and durability. The abundance of active N and P species and the porous structure may be responsible for this catalyst's high ORR performance. The present work provides a facile way of using economical, environmentally friendly, and renewable biomass to develop a high-activity cathode electrocatalyst for fuel cell applications.

Effects of different ratios and storage periods of liquid brewer's yeast mixed with cassava pulp on chemical composition, fermentation quality and in vitro ruminal fermentation.

ObjectiveThis study aims to evaluate the chemical composition, fermentation quality and in vitro ruminal fermentation of various ratios and storage periods of liquid brewer’s yeast (LBY) mixed with cassava pulp (CVP).MethodsFour mixtures of fresh LBY and CVP were made (LBY0, LBY10, LBY20, and LBY30 for LBY:CVP at 0:100, 10:90, 20:80, and 30:70, respectively) on a fresh matter basis, in 500 g in plastic bags and stored at 30 to 32°C. After storage, the bags were opened weekly from weeks 0 to 4. Fermentation quality and in vitro gas production (IVGP) were determined, as well as the dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), neutral detergent fiber, acid detergent fiber and acid detergent lignin contents.ResultsThe contents of CP and EE increased, whereas all other components decreased, in proportion to LBY inclusion (p<0.01). The DM and OM contents gradually decreased in weeks 3 and 4 (p<0.05), while EE contents were lowest in week 0. The pH, ammonia nitrogen per total nitrogen (NH3-N/TN) and V-score in each mixture and storage period demonstrated superior fermentation quality (pH≤4.2, NH3-N/TN≤12.5%, and V-score>90%). The pH increased and NH3-N/TN decreased, with proportionate increases of LBY, whereas the pH decreased and NH3-N/TN increased, as the storage periods were extended (p<0.01). Although IVGP decreased in proportion to the amount of LBY inclusion (p<0.01), in vitro organic matter digestibility (IVOMD) was unaffected by the mixture ratios. The highest IVGP and IVOMD were observed in week 0 (p<0.01).ConclusionThe inclusion of LBY (as high as 30%) into CVP improves the chemical composition of the mixture, thereby increasing the CP content, while decreasing IVGP, without decreasing fermentation quality and IVOMD. In addition, a preservation period of up to four weeks can guarantee superior fermentation quality in all types of mixtures. Therefore, we recommend limiting the use of CVP as a feed ingredient, given its low nutritional value and improving feed quality with the inclusion of LBY.

A New Approach for Detecting Spoilage Yeast in Pure Bottom-Fermenting and Pure Torulaspora Delbrueckii Pitching Yeast, Propagation Yeast, and Finished Beer

Beer quality is highly dependent upon yeast condition. Consequently, breweries should consider the quality of the pitching yeast. Spoilage yeasts such as wild types of Saccharomyces cerevisiae, S. cerevisiae var. diastaticus, and some non-Saccharomyces yeasts occur occasionally in pitching yeast and as secondary final-product contaminants. They negatively impact pitching yeast fermentation and beer flavor. In this study we used a novel device to measure the pressure in small-scale fermentation vessels and to detect five spoilage yeast strains of S. cerevisiae var. diastaticus in four pure pitching yeast strains of the brewing yeast Torulaspora delbrueckii. We investigated a method to detect the five spoilage yeasts in pure pitching yeast of four S. pastorianus strains. Pitching yeast was chosen for its high cell density, activity, adaptability, and therefore stress resistance, and because it could produce false positive results in the detection method. Cultivation in the vessel at 37°C in YM broth inhibited all the pitching yeasts but increased the spoilage yeast. Real-time polymerase chain reaction validated the method. Low spoilage yeast concentrations of 10 cells/mL and contaminated industrial samples were reliably detected. Minimal time was needed to prepare the sample and detect spoilage yeasts.

Suitability of monotypic and mixed diets for Anopheles hermsi larval development.

The developmental time and survival to eclosion of Anopheles hermsi Barr & Guptavanij fed monotypic and mixed diets of ten food types were examined in laboratory studies. Larvae fed monotypic diets containing animal detritus (freeze-dried rotifers, freeze-dried Daphnia pulicaria, and TetraMin® fish food flakes) and the mixotrophic protistan Cryptomonas ovata developed faster and survived better than larvae that were fed other monotypic diets. Survival to adulthood of larvae fed several concentrations of the diatom Planothidium (=Achnanthes) lanceolatum was poor (<13%) and larval development time was approximately twice that of larvae fed TetraMin® fish food flakes, the standard laboratory diet. Larvae fed monotypic diets containing prokaryotes (bacteria [Bacillus cereus] and cyanobacteria [Oscillatoria prolifera]) and brewer's yeast (Saccharomyces cerevisiae) failed to survive beyond the 1(st) and 2(nd) instar, respectively. Larvae fed only chlorophytes, single-celled Chlamydomonas reinhardtii and filamentous Spirogyra communis, failed to complete larval development, regardless of the concentration tested. Cohorts fed a combination of food types (mixed diets) usually developed better than cohorts fed monotypic diets. Food types that failed to support complete development when fed alone often facilitated development to adulthood when fed in combination with food types containing >1% C20 polyunsaturated fatty acids as total fat, but regardless of essential fatty acid content, algae that produced mucilage and filaments that sank out of the feeding zone were poor quality diets.

Sexual receptivity ofAnastrepha obliqua(Diptera: Tephritidae) wild females affected by nutrition and egg load

The influence of feeding, egg load and stage of ovarian development on the sexual receptivity of some insect species has been reported. This work investigated the effects of different brewer's yeast concentrations in the diet offered to females of West Indian fruit fly, Anastrepha obliqua, on their sexual receptivity. Wild females were fed on artificial diets containing 2.0 g brewer's yeast per 100 mL of water (low-yeast diet, LY diet), 6.5 g yeast per 100 mL of water (high-yeast diet, HY diet) or only sucrose (Su diet) and then placed with the males. Female sexual receptivity tests were carried out in acrylic boxes in the laboratory under controlled conditions (temperature, humidity and light). Females fed on the HY diet were more sexually receptive to male courtship than the other females. Additionally, when fed on the same diet (HY diet), those females with higher egg load were more sexually receptive. The data suggest that the ingestion of a protein source is essential for increasing sexual receptivity and that egg load is the most important factor affecting sexual receptivity of A. obliqua females.

Genome annotation of a Saccharomyces sp. lager brewer's yeast

The genome of lager brewer's yeast is a hybrid, with Saccharomyces eubayanus and Saccharomyces cerevisiae as sub-genomes. Due to their specific use in the beer industry, relatively little information is available. The genome of brewing yeast was sequenced and annotated in this study. We obtained a genome size of 22.7Mbp that consisted of 133 scaffolds, with 65 scaffolds larger than 10kbp. With respect to the annotation, 9939 genes were obtained, and when they were submitted to a local alignment, we found that 53.93% of these genes corresponded to S. cerevisiae, while another 42.86% originated from S. eubayanus. Our results confirm that our strain is a hybrid of at least two different genomes.

Defective quiescence entry promotes the fermentation performance of bottom-fermenting brewer's yeast

One of the key processes in making beer is fermentation. In the fermentation process, brewer's yeast plays an essential role in both the production of ethanol and the flavor profile of beer. Therefore, the mechanism of ethanol fermentation by of brewer's yeast is attracting much attention. The high ethanol productivity of sake yeast has provided a good basis from which to investigate the factors that regulate the fermentation rates of brewer's yeast. Recent studies found that the elevated fermentation rate of sake Saccharomyces cerevisiae species is closely related to a defective transition from vegetative growth to the quiescent (G0) state. In the present study, to clarify the relationship between the fermentation rate of brewer's yeast and entry into G0, we constructed two types of mutant of the bottom-fermenting brewer's yeast Saccharomyces pastorianus Weihenstephan 34/70: a RIM15 gene disruptant that was defective in entry into G0; and a CLN3ΔPEST mutant, in which the G1 cyclin Cln3p accumulated at high levels. Both strains exhibited higher fermentation rates under high-maltose medium or high-gravity wort conditions (20° Plato) as compared with the wild-type strain. Furthermore, G1 arrest and/or G0 entry were defective in both the RIM15 disruptant and the CLN3ΔPEST mutant as compared with the wild-type strain. Taken together, these results indicate that regulation of the G0/G1 transition might govern the fermentation rate of bottom-fermenting brewer's yeast in high-gravity wort.

Investigation of dependence of honey drinking physical, chemical and organoleptic characteristics from the raw materials chemical composition and conditions of fermentation process

The important task of drink fermented from honey production from local varieties of honey in this review is processed. The present state of drink growing was reviewed. New recipes by beverages has been processed. Data on the range of drink fermented from honey that are produced in Ukraine was shown. The suitability of Ukrainian varieties of honey for beverages production was found. This review describes the synthetic methodologies for drinks. The dynamics of the honey solution fermentation has been investigated. It was established, that the process of fermentation of honey wort is uneven. . The influence of the main factors (raw materials composition, concentration of yeasts) on the process of fermentation and physical as well as chemical properties obtained drink have been studed. To reduce the duration of fermentation using yeast it is recommended to use brewer's yeast genus Schizosaccharomyces, prepared by a special recipe, which greatly reduces the lag phase of yeast propagation, intensifies the flow of honey wort fermentation and positively affects the tasting characteristics of drink. Reviewed quality beverage received the results of sensory analysis. Depending on the raw material composition and production method the drink with broad range of taste can be obtained. The chemical composition and harmony of drink fermented from honey taste are optimized. The resulting drinks have improved organoleptic properties and can be offered for the production in the industry

Growth performance, serum thiocyanate and haematological indices of pigs fed whole cassava chips supplemented with brewer's yeast

An experiment was conducted to evaluate the growth performance, serum thiocyanate and haematological indices of pigs fed Whole Cassava Chips (WCC) supplemented with brewer's yeast as substitute to maize in a twelve weeks feeding trial. Forty-eight crossbred growing pigs of Landrace and Hampshire breeds averaging 21.14kg liveweight and approximately 12 wk old were allotted to three dietary treatments with four replicates each of four pigs per replicate. The dietary treatments are Diet 1 which is a maize based Positive control(MB), Diet 2 was a Whole Cassava chips based diet without supplementation Negative control(WCC) while Diet 3 contained whole cassava chips with brewer' s yeast respectively(WCC x BY).Results revealed a significant Average Feed Intake (AFI) ranged from (2.17 to 2.48kg/day). The Pigs fed WCC meal without brewer' s yeast (diet 2) had the highest AFI while pigs fed Diet 1 had the least intake. Daily weight gain increased with brewer' s yeast supplementation (0.400 to 0.463kg). The feed to gain ratio was significantly (p<0.05) affected by the dietary treatments with values ranging from 4.92to 5.90 and best value obtained with pigs fed WCC meal with brewer' s yeast (WCC x BY). The haematological indices such as Packed Cell Volume (PCV), Haemoglobin Concentration (Hb), White Blood Cell (WBC), and Red Blood Cell (RBC) counts obtained for the pigs fed MB and those on diet WCC x BY were significantly (p<0.05) better than those on WCC diet. Serum thiocyanate concentration of pigs fed diet 3 (WCC with brewer' s yeast) increased significantly (0.00 to 1.79mg/100ml). Results showed that supplementing whole cassava chips with 10% brewer' s yeast had a beneficial effect as an additive in diets of growing pigs. Keywords: Blood, Cyanogens, Growth, Nutritional effect.

Nutritional ingredients from spent brewer's yeast obtained by hydrolysis and selective membrane filtration integrated in a pilot process

Spent brewer's yeast is a natural surplus from brewing industry. In order to up-grade this by-product, isolation of compounds has been tentatively assessed. The main objective of this work focuses on the use of ultrafiltration and nanofiltration pilot system for recovering cell compounds. Initially, yeast was autolyzed and ultrafiltered with a 10 kDa cut-off, and the two fractions obtained were hydrolyzed with Cynara cardunculus extract and nanofiltered with 3 kDa cut-off. Four fractions with different molecular weights were obtained, with protein and sugar contents ranging between 30–69% and 20–48%, respectively. Sodium and potassium were the major minerals present, whereas glutamine, glutamic acid and alanine, the most representative free amino acids. Peptide profile showed peptides with hydrophilic and hydrophobic characteristics, usually associated with biological activities, including antihypertensive and antioxidant. Thus, based on their compositions, all fractions show technological and biological potential, and can be used as nutritional ingredients in food and feed.

Screening the Hydroxylation of Fatty Acids with Lactic Acid Bacteria Based on the Lactonization of the Hydroxylated Products

Hydroxyl fatty acids (HFAs) are used for the production of artificial food flavorings and alcoholic beverages. In this study, we screened a series of hydroxylating lactic acid bacteria (LAB) by using a rapid screening method based on the lactonization of the products with brewing yeast. γ-Lactones have a fruity aroma with a low detection threshold, meaning that they can be readily detected by sniffing without the need for GC-MS analysis. LAB can be used to hydroxylate fatty acids, which can be lactonized with brewing yeast for detection with the sniffing method. Commercial yeast strains were cultivated in the presence of HFAs, and lactone-producing strains were detected by sniffing. Beer brewing yeast T-58 gave the highest level of γ-lactone from ricinoleic acid (>90%). Strains of LAB capable of converting unsaturated fatty acids to HFAs were screened with T-58 yeast. The Y-20 strain was determined to be the best LAB and converted oleic acid to 10-hydroxystearic acid. It was subsequently identified as Lactobacillus sakei. Notably, this LAB hydroxylated over 90% of the oleic acid in the medium at 15°C after 30–48 h. These results therefore suggest that the Y-20 strain could be used to hydroxylate fatty acids for alcoholic beverages.

Characterization of YML020W in Saccharomyces cerevisiae

Saccharomyces cerevisiae is a single‐celled, eukaryotic yeast commonly known as baker's or brewer's yeast. As a model organism, genes can be easily inserted and removed allowing researchers to utilize deletion genetics to better understand the function of open reading frames (ORFs) within the S. cerevisiae genome. ORFs are characterized using gene ontology, which includes three categories: biological processes, cellular components, and molecular functions. The characterization of genes within the S. cerevisiae genome is of importance in order to understand the functionality of these uncharacterized genes. Through a better understanding of how genes and their products interact with one another, we can gain insight into the function of S. cerevisiae as a model organism. The purpose of this study is to characterize the S. cerevisiae ORF YML020W, which was first identified in a screen for resistance to the apoptosis‐inducing drug, KP1019. In order to further the understanding of the structure and function of this ORF, a deletion strain of YML020W was constructed. Genetic interactions with DUN1 and YML020W were characterized through the construction of a double deletion mutant. To determine the location of the gene within the cell, the protein product associated with YML020W was fluorescently labeled at the C‐terminus and observed using fluorescence microscopy where clusters of YML020Wp were visible. These strategies will add details to gene ontology and provide information concerning of the importance of YML020W in S. cerevisiae.Support or Funding InformationThis work was supported by Juniata College, Howard Hughes Medical Institute, and the National Science Foundation

Microbial Populations in Naked Neck Chicken Ceca Raised on Pasture Flock Fed with Commercial Yeast Cell Wall Prebiotics via an Illumina MiSeq Platform.

Prebiotics are non-digestible carbohydrate dietary supplements that selectively stimulate the growth of one or more beneficial bacteria in the gastrointestinal tract of the host. These bacteria can inhibit colonization of pathogenic bacteria by producing antimicrobial substances such as short chain fatty acids (SCFAs) and competing for niches with pathogens within the gut. Pasture flock chickens are generally raised outdoors with fresh grass, sunlight and air, which represents different environmental growth conditions compared to conventionally raised chickens. The purpose of this study was to evaluate the difference in microbial populations from naked neck chicken ceca fed with commercial prebiotics derived from brewer’s yeast cell wall via an Illumina MiSeq platform. A total of 147 day-of-hatch naked neck chickens were distributed into 3 groups consisted of 1) C: control (no prebiotic), 2) T1: Biolex® MB40 with 0.2%, and 3) T2: Leiber® ExCel with 0.2%, consistently supplemented prebiotics during the experimental period. At 8 weeks, a total of 15 birds from each group were randomly selected and ceca removed for DNA extraction. The Illumina Miseq platform based on V4 region of 16S rRNA gene was applied for microbiome analysis. Both treatments exhibited limited impact on the microbial populations at the phylum level, with no significant differences in the OTU number of Bacteroidetes among groups and an increase of Proteobacteria OTUs for the T1 (Biolex® MB40) group. In addition there was a significant increase of genus Faecalibacterium OTU, phylum Firmicutes. According to the development of next generation sequencing (NGS), microbiome analysis based on 16S rRNA gene proved to be informative on the prebiotic impact on poultry gut microbiota in pasture-raised naked neck birds.

Terminal acidic shock inhibits sour beer bottle conditioning by Saccharomyces cerevisiae

During beer fermentation, the brewer's yeast Saccharomyces cerevisiae experiences a variety of shifting growth conditions, culminating in a low-oxygen, low-nutrient, high-ethanol, acidic environment. In beers that are bottle conditioned (i.e., carbonated in the bottle by supplying yeast with a small amount of sugar to metabolize into CO2), the S. cerevisiae cells must overcome these stressors to perform the ultimate act in beer production. However, medium shock caused by any of these variables can slow, stall, or even kill the yeast, resulting in production delays and economic losses. Here, we describe a medium shock caused by high lactic acid levels in an American sour beer, which we refer to as “terminal acidic shock”. Yeast exposed to this shock failed to bottle condition the beer, though they remained viable. The effects of low pH/high [lactic acid] conditions on the growth of six different brewing strains of S. cerevisiae were characterized, and we developed a method to adapt the yeast to growth in acidic beer, enabling proper bottle conditioning. Our findings will aid in the production of sour-style beers, a trending category in the American craft beer scene.