Growth and survival of foodborne pathogens in beer

This work aimed to assess the growth and survival of four foodborne pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, Listeria monocytogenes, and Staphylococcus aureus) in beer. The effects of ethanol, pH, and storage temperature were investigated for the gram-negative pathogens (E. coli O157:H7 and Salmonella Typhimurium), whereas the presence of hops ensured that the gram-positive pathogens (L. monocytogenes and S. aureus) were rapidly inactivated in alcohol-free beer. The pathogens E. coli O157:H7 and Salmonella Typhimurium could not grow in the mid-strength or full-strength beers, although they could survive for more than 30 days in the mid-strength beer when held at 4°C. These pathogens grew rapidly in the alcohol-free beer; however, growth was prevented when the pH of the alcohol-free beer was lowered from the "as received" value of 4.3 to 4.0. Pathogen survival in all beers was prolonged at lowered storage temperatures.     

FUNDAMENTALS OF IMMOBILISED YEAST CELLS FOR CONTINUOUS BEER FERMENTATION: A REVIEW

Recent fundamental research conducted on immobilised cells with a focus on continuous primary beer fermentation is presented in this review. The knowledge of whole-cell immobilisation, continuous fermentation, yeast biochemistry associated with beer flavour production, and bioreactor engineering design is required to apply immobilised yeast cells for industrial scale beer production. Understanding how immobilisation and continuous bioreactor operation affect yeast cell metabolism and viability will provide the groundwork for optimising beer quality. The latest studies on immobilised cell carriers, viability, vitality, mass transfer characteristics and bioreactor design indicate that an industrial scale immobilised cell system for primary beer fermentation may soon be a reality in the modern brewery .     

啤酒酵母絮凝机理研究进展

啤酒酵母絮凝机理的假说有絮凝共生假说、类外源凝集素假说、类外源絮凝素假说等。啤酒酵母絮凝表型可分为FLO1型和NewFLO型;对啤酒酵母絮凝基因的研究有结构基因——见O基因家族、调节基因及其他相关絮凝基因。对啤酒酵母絮凝性状的改良研究可应用于调控啤酒酵母絮凝性状,利于啤酒生产;利用酵母絮凝性状构建絮凝选择栽体;利用絮凝素蛋白构建酵母细胞表层展示体系;利用酵母絮凝蛋白对细菌的吸附,应用于医疗行业。     

无酒精啤酒的研究

<正> 无酒精啤酒是一种酒精度低于1 w/w％的饮料,它具有啤酒的色、香、味。因其酒精度低特别适于司机、运动员、孕妇、儿童及老年人饮用。无酒精啤酒的生产方法已有许多,但各自又存在着一定的问题,本论文的目在: 1.选出控制或除去酒精的有效方法。 2.以气相色谱法测定风味物质,对产品的风味进行改善。     

Optimisation of High Gravity and Diet Beer Production in a German Brewery by Flow Cytometry

Increasing the quantity of beer production without diminishing the quality of the product is a key concern of the beer producing industry. Modifications to the brewery's equipment and settings are the most commonly used methods to improve the brewing process, while the supreme importance of the physiological state of the beer producing organisms, the yeast cells, for the productivity of the brewing process is often poorly recognised. The work described here was designed to optimise two processes: the inoculation regime used to produce high gravity bottom-fermenting beer, and the production of high quality diet beer. To achieve these aims, flow cytometry was used to follow changes in the distribution of DNA, neutral lipid and 3β-hydroxsterol contents in Saccharomyces carlsbergensis strains during inoculation, fermentation and storage. This allowed potential time-saving alterations in the process to be identified. Double staining techniques proved that vigorous fermentative activity and long-term survival capacity during main and secondary fermentation requires intense multiplication of the yeast cells during inoculation. The production of high gravity beer was then enhanced by altering the schedule of the wort additions, and thus increasing the yeast's activities related to multiplication. To produce diet beer, oligosaccharides that remain after the standard brewing process are degraded by adding small amounts of wort, usually during secondary fermentation. However, during this period of fermentation the physiological activity of the yeast cells is hampered by low carbon and high ethanol concentrations. Adding small batches of wort at carefully defined time points and in optimised amounts, even during the main fermentation, improves the physiological state of the yeast cells and rapidly decreases the carbon concentration within the fermentation tank. Both of these factors help to promote quick fermentation to a high quality diet beer. Thus, the flow cytometric investigations provided a reliable basis for identifying effective means of improving the process regime for brewing both of these products.     

Investigating the Antimicrobial Efficacy of a Lactococcal Bacteriocin for the Development of Microbiologically Stable Beer

Barley isolate Lactococcus lactis M30 produces an antimicrobial proteinaceous activity, which at least under laboratory conditions was shown to target beer spoiling lactic acid bacteria, including Lactobacillus brevis BSH9. The aim of this study was to investigate the application of this antibacterial activity at various stages of the brewing process and in packaged beer. Lactococcus lactis M30 was shown to produce the antimicrobial activity during growth under specific conditions in fortified unhopped wort. However, this activity was lost during wort boiling and yeast fermentation. When the bacteriocin was added directly to beer it retained in vitro activity following pasteurisation, while it was also shown to inhibit growth in situ when pasteurised beer was challenged with low levels of the beer spoiling Lactobacillus brevis BSH9 culture. The capacity of the bacteriocin to prevent microbial spoilage of beer was tested at various temperatures over a period of seven weeks. Storage of bacteriocin‐containing beer at 30°C or room temperature resulted in a decrease in antimicrobial activity over time, but when refrigerated or frozen, this beer retained sufficient activity to be effective against Lactobacillus brevis BSH9.     

Yeast flocculation: Flocculation onset and receptor availability

Flocculent strains of brewing yeast grow and ferment as single cells and flocculate in the stationary phase of growth. The switch from single-celled yeast growth to multi-celled aggregation, flocculation onset, is of critical importance to the brewing industry. Yeast flocculation involves adhesion of surface-lectins on flocculent cells to carbohydrate receptors on neighbouring cell-walls. The presence of carbohydrate receptors, outer-chain mannan side-branches, was monitored throughout growth of flocculent and non-flocculent strains of Saccharomyces cerevisiae, with particular attention to the growth phases where flocculation is normally developed. Receptors were probed by coflocculation with flocculent strains and by aggregation with concanavalin A, a lectin shown to use the same receptors as flocculation. While considerable variation was found in coflocculation and concanavalin A aggregation between strains, little or no change in receptor availability was found throughout the growth of all yeast strains. Yeast cells could easily be coflocculated at any growth stage. It was concluded that receptor availability is not involved in the process of flocculation onset.     

SUPPRESSION OF α-ACETOLACTATE FORMATION IN BREWING WITH IMMOBILIZED YEAST

Immobilized yeast cells extensively produced the diacetyl precursor, α-acetolactate, during alcohol fermentation. The activity of acetohydroxy acid synthetase, which is responsible for the formation of α-acetolactate from pyruvic acid, was high in cell-free extracts of immobilized yeast cells compared with that of free yeast cells. It was suggested that the expression of AHA synthase of immobilized yeast cells was increased during growth in the carrier as compared with free yeast cells. When the initial immobilizing yeast cell concentration was changed from 1.0 × 10⁶ cells/ml to 1.0 × 10⁹ cells/ml, production of α-acetolactate was reduced from 0.94 mg/l to 0.30 mg/l. Furthermore, during continuous fermentation for 10 d, the concentration of α-acetolactate in beer was 0.30 mg/l.     

NEW DEVELOPMENTS IN THE BREWING INDUSTRY USING IMMOBILISED YEAST CELL BIOREACTOR SYSTEMS*

The use of immobilised yeast cell systems in industry has been extensively reported in the literature. The brewing industry is closely examining immobilisation technology and evaluating its merits. Various immobilisation methods are available to researchers and the nature of the application often dictates the choice of an immobilisation matrix. Industrial scale systems utilising immobilised yeast cells adsorbed to pre-formed carriers have been used for the production of low alcohol beers and for maturation or secondary fermentation of beer. Research relating to the primary fermentation of beer continues and several groups have developed laboratory scale systems. An overview of the respective technologies is provided and several relevant industrial applications cited .     

无醇啤酒的生产工艺及其质量特性

本文比较了市售无醇啤酒、自制的限制发酵无醇啤酒和正常啤酒的理化指标,总结了各种生产工艺的特点。企业应该根据自身情况确定无醇啤酒生产方法。     

啤酒酵母絮凝影响因素及改善途径的研究概况

啤酒酵母的絮凝性对啤酒生产具有重要意义,不仅影响啤酒的发酵过程也会影响啤酒口感和风味。对啤酒酵母絮凝的国内外最新研究进展和成果进行综述,包括絮凝机理假说,影响絮凝因素,酵母絮凝对啤酒品质和风味影响,改善絮凝途径,期望解决实际啤酒工业生产中酵母异常絮凝出现的一系列问题。     

Simulation of vacuum distillation to produce alcohol-free beer

Several processes have been developed for producing alcohol-free beer while maintaining desirable sensory characteristics. One of the most popular thermal processes used is distillation, where not only ethanol but volatile aromatic components are partly or completely removed from the beer. Based on data from the literature and using the Aspen Plus simulator, this study evaluates and compares the aroma profiles of alcohol-free beers obtained by continuous vacuum distillation with different pressures and processes. Three processes were simulated at pressures of 60, 102, and 200 mbar. The first (Process A) was a standard continuous vacuum distillation, where the bottom product was an alcohol-free beer. In the second (Process B), the bottom product was blended with a standard beer that had not undergone any thermal process. In the third (Process C), part of the top stream was mixed with the bottom product. This study considered eight major compounds in beer: ethanol, propanol, isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol, ethyl acetate, diacetyl and isoamyl acetate. The three simulated pressure ranges showed similar results, indicating that reducing the pressure below 200 mbar did not improve separation. Further, vacuum distillation did not remove diacetyl from the beer. Processes B and C resulted in beer that was richer in flavour compounds. Furthermore, when these processes were compared to Process A, the concentration of esters was markedly higher. © 2019 The Institute of Brewing & Distilling     

SOME CONSIDERATIONS OF THE FLOCCULATION CHARACTERISTICS OF ALE AND LAGER YEAST STRAINS*

While some ale yeast strains are able to flocculate when cultured in a defined medium of glucose, ammonium salts, vitamins and ions, others require the presence of a nitrogen-containing inducer in the growth medium. On the other hand, all flocculent lager strains examined to date are able to flocculate after being cultured in a defined medium and do not appear to require the addition of inducer material to the growth medium. The inducer material present in wort has been identified as peptide. By the use of ion exchange chromatography the peptide fraction that induces flocculation has been found to contain a high level of acidic amino acid residues with a very similar structure to that reported for the α-factor involved in sexual agglutination of haploid α and a cells of Sacch. cerevisiae. Studies on the adsorption of Ca⁺⁺ ion by the cell wall failed to reveal any significant differences in total uptake between flocculent and non-flocculent cultures. It would appear that Ca⁺⁺ ions are bound less tightly by non-flocculent cells than by flocculent cells. The contribution of calcium to flocculation is not the absolute amount of this ion adsorbed by the yeast cell wall but rather the stereo-specific manner by which it is bound, i.e., its position relative to the three-dimensional structure of the yeast cell wall.     

Evaluation of the fermentative potential of Candida zemplinina yeasts for craft beer fermentation

The fermentative potential of Candida zemplinina Y.01667 and Y.01670 was evaluated to explore the potential use of these yeasts for craft beer fermentations. Fermentation experiments were carried out at different temperatures and soluble solid concentrations, using synthetic media with glucose syrup as a sugar source and with a laboratory malt wort plus different adjuncts. Results showed that both strains fermented well at 14 °C and had improved fermentative activity at 20 °C. The fermentative kinetics of C. zemplinina Y.01667 and Y.01670 were not affected when experiments at higher concentrations of soluble solids were conducted. Furthermore, C. zemplinina strains had better growth, higher viable cells counts, less free amino nitrogen consumption, lower sedimentation rates and slighter changes in pH values, when compared with results of the lager beer yeast Saccharomyces cerevisiae S‐23 in the synthetic medium tested. Fermentations in a malt wort with different adjuncts indicated that C. zemplinina Y.01670 could possibly be used as a yeast in craft beer production. Copyright © 2016 The Institute of Brewing & Distilling     

125th Anniversary Review: Yeast Flocculation and Sedimentation in Brewing

Flocculation is prerequisite for bulk sedimentation of yeast during brewery fermentation. Although single yeast cells gradually sediment in green beer, this sedimentation rate is too slow without formation of large yeast flocs. The present review concerns the major determinants of yeast flocculation and sedimentation in brewery fermentations. Flocculation characteristics of yeast are strongly strain‐dependent and largely defined by which FLO genes are functional in each strain. In addition to the genetic background, several environmental factors affect flocculation. These can be, somewhat arbitrarily, classified as physiological factors, such as the calcium availability, pH, temperature and ethanol and oxygen concentrations in the medium or physical factors, such as cell surface hydrophobicity, cell surface charge and the presence of appropriate hydrodynamic conditions for the formation of large flocs. Once yeast flocs are formed, their size, shape and density and the properties of the surrounding medium affect the rate at which the flocs sediment. Higher gravity worts usually result in green beers with higher viscosity and density, which both retard sedimentation. Moreover, environmental factors during yeast handling before fermentation, e.g., propagation, storage and cropping, influence the flocculation potential of yeast in subsequent fermentation. Premature yeast flocculation (PYF) and the role of PYF factors are discussed. In conclusion, some potential options available to adjust yeast flocculation are described.     

Lipid Turnover During Inverse Flocculation in Saccharomyces cerevisiae UOFS Y‐2330

In this study we uncovered that Saccharomyces cerevisiae UOFS Y‐2330 does not only demonstrate inverse flocculation, but is also characterised by two different lipid turnover patterns. During Flo1 phenotype flocculation, this yeast showed two neutral lipid accumulating stages (i.e. at 8 h and from 12 h). This is probably triggered by flocculation, which can be regarded as a survival mechanism where cells accumulate predominantly neutral lipids as a reserve energy source — a similar mechanism is probably operative when cells enter stationary growth. Contrary to Flo1 behaviour, this strain in NewFlo phenotype mode demonstrates only a single lipid accumulation phase i.e. when cells enter stationary growth, which coincides with increase in flocculation. In addition, an increase in phospholipids was experienced during active growth in both flocculation behaviours i.e. Flo1 and NewFlo probably as a result of active membrane production.     

ON THE MEASUREMENT OF THE FLOCCULATION CHARACTERISTICS OF BREWERS' YEAST

The capacity of certain yeast strains to flocculate is important to the brewing industry. So is the determination of the flocculation characteristics of a yeast strain. In this study we subdivided the flocculation characteristics into three phenomena. A proposal for the most suitable method to quantify each phenomenon is given. For this, four parameters (bond strength, floc size, settling rate and number of single cells) that serve as a measure to these phenomena have been studied. Next to this, attention is payed to the influence of environmental conditions (temperature, calcium concentration, pH and the hydrodynamic conditions during the test) on the result of the test. During this part of the study the flocculence of the yeast cells was constant, so the effect of the yeast on the results of the test is excluded. It turned out that the temperature of the medium and the hydrodynamic conditions during the test most strongly influence floc formation. Next to this, medium viscosity is important if the flocculation characteristics are quantified via settling experiments.     

Lachancea thermotolerans as an alternative yeast for the production of beer

The ability of Lachancea thermotolerans strains to ferment brewer's wort has been investigated. Initial fermentations with three L. thermotolerans strains compared the use of maltose and maltotriose, as well as production of glycerol and lactic acid and pH evolution over the course of the fermentation. The most promising strain was subsequently tested for additional traits important for beer production, including pitching rate, generational capacity, foam stability, hop tolerance, vicinal diketone production, oxygen requirement and flocculation. These tests suggest that L. thermotolerans may be a good choice for producing sour beers in a single fermentation step without the use of lactic acid bacteria. Copyright © 2016 The Institute of Brewing & Distilling     

CALCIUM IN FLOCCULENCE OF SACCHAROMYCES CEREVISIAE

A quantitative method was adopted for measuring flocculation intensity of yeast photometrically. In three strongly flocculent strains of Saccharomyces cerevisiae examined with this method, flocculation intensity depended on ionic strength of the medium as well as on Ca concentration, and was maximum at about 0·01 ionic strength. At this optimum ionic strength, when free Ca concentration was varied in stabilized complexing systems, a transition occurred at about 10^?8 m Ca between flocculent and nonflocculent states. At higher Ca concentrations, flocculation intensity was nearly constant. The observed transition is at much lower Ca levels than other effects noted in the literature.     

STUDY OF THE FLOCCULATION OF SACCHAROMYCES DIASTATICUS NCYC 625

Yeast flocculation presents a great interest for the industry of fermentation but its mechanism is still not fully understood. In order to enlighten this mechanism, the flocculation of Saccharomyces diastaticus NCYC 625 was studied. As with other Saccharomyces strains, the effects of different factors affecting flocculation and deflocculation (pH, temperature, medium, EDTA, cations…) suggest a lectin-like binding between adjoining cells. The genetic determinism of flocculation is nuclear and not mitochondrial. Although Saccharomyces diastaticus NCYC 625 could be classified in the FLO1 phenotype according to Stratford and Assinder⁴², allelism tests show that the gene involved in the flocculation control is not allelic with FLO1 or FLO5 and possibly different from FLO8 .