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Fermented beverages such as beer are known for their relatively long shelf life. However, the main factor limiting their shelf life is the qualitative changes that occur during storage. From the moment the beer is produced, its characteristics, such as taste, aroma, and colloidal stability undergo continuous change. The intensity of these changes depends on the type of beer, storage conditions, and length of storage. While some degree of ageing can have a positive influence on sensory characteristics of a beer, beer stalling is seen as a significant problem. As it is currently understood, beer ageing is mainly caused by the formation of stalling aldehydes. At the same time, compounds which bestow the beer its flavour, such as esters, terpenes, and iso-α-acids undergo qualitative and quantitative changes. As a result, aroma discriminants such as freshness, fruitiness or florality are often lost over time. In their place, aromas described as ribes, cardboard, bread-like, honey-like or sherry-like appear. The article aims to present the changes in beer sensorial, physicochemical, and microbiological characteristics during storage and the factors that affect beer quality during ageing The article also describes the variables which according to the current literature, may alter the flavour stability of a beer.

Besides providing bitterness to beer, hops also impart a whole range of aromas, such as herbal, spice, floral, citrus, fruity and pine to this beverage. Although hops are usually added in relatively small amounts, they have a significant impact on the sensory characteristics of the product. Raw hop aroma significantly differs from the aroma resulting from its addition to the beer. The final aroma of the beer arises from substances in the malt, hops, other additives, and yeast metabolism. The biochemical transformation of hop compounds by yeast has become more and more popular in recent years. Knowledge of this process may allow more precise control over the final sensory characteristics of the beverage. The article describes the chemical composition of hops and discusses the influence of the hopping regime on the concentration of volatile compounds in the finished product. Moreover, the article describes the biotransformation of hop-derived compounds by traditionally used Saccharomyces cerevisiae yeast, as well as less commonly used non-Saccharomyces yeast. The paper outlines the current state of knowledge on biotransformation of hop-derived hydrocarbons, terpenoids, esters, sulfur compounds and glycosidically bound aroma precursors.

In recent years, demand for low-alcohol and alcohol-free beers has been rising. Of the many methods of producing such beers, many have expensive implementation requirements or drawbacks in terms of beer quality. The exploration of non-Saccharomyces yeast species presents a promising opportunity to overcome these challenges. These yeasts, with their diverse metabolic capabilities and unique flavor profiles, offer the potential to create innovative and flavorful low-alcohol beers. The study investigates the feasibility of using selected non-Saccharomyces yeasts for brewing low-alcohol beers, focusing on fermentation kinetics, physicochemical parameters, and the sensory attributes of the final product. The evaluated yeast species were Kluyveromyces lactis MG971263, Metschnikowia pulcherrima MG971247 and MG971250, Torulaspora delbrueckii MG971248, Wickerhamomyces anomalus MG971261, and W. onychis MG971246. Two strains of Saccharomyces cerevisiae were used as a control. The results of the study show that selected non-Saccharomyces yeast species might be used to produce low-alcohol beers. The non-Saccharomyces yeast allowed the researchers to obtain beers with an alcohol content in the range of 0.5–1.05%, while the control beer brewed with US-05 had an alcohol content of 3.77%. Among the evaluated strains, the strains M. pulcherrima MG971250 and T. delbrueckii MG971248 were found to be rated better in a sensory evaluation than the brewed and low-alcohol strains of S. cerevisiae. [ABSTRACT FROM AUTHOR]

Featured Application: Screening for new yeast species may to ease the production of no/low-alcohol beers or may enable the obtaining of beers with unique sensory characteristics. Among many methods to produce low/no-alcohol beers, using special yeasts has gained a substantial interest in the brewing industry. This approach relies on the fact that many non-Saccharomyces yeasts do not utilize maltose, which is the main sugar found in brewer's wort. Additionally, these yeasts may allow the production of a beer with unique sensory characteristics. The aim of the study was to evaluate the potential of 18 non-Saccharomyces yeast strains in the production of low-alcohol beer. As a control strain, S. cerevisiae US-05 was used. The study consisted of two parts: microbiological evaluation and small-scale fermentations. In the microbiological part, ability to ferment sugars found in a wort, resistance to stress factors, phenolic off-flavor production, and enzymatic activities of β-glucosidase and β-lyase were evaluated. In the second part of the study, yeasts were used to produce a beer from 9.3 °Plato wort. During the fermentation, its dynamics was analyzed. The obtained beers were analyzed regarding their alcohol content, pH, acidity, and color. All of the evaluated strains produced low levels of alcohol. Two of the evaluated strains were characterized by especially high β-glucosidase activity. Based on the obtained results, six of the evaluated strains are promising in brewing. [ABSTRACT FROM AUTHOR]

The objective of this paper was to test the potential of selected non-Saccharomyces strains for beer production, by using Saccharomyces cerevisiae as a control sample. For some of variants brewing enzymes were added to wort to increase the content of fermentable sugars. The non-Saccharomyces yeasts differed in the fermentation process rate. The basic beer physiochemical parameters were assessed, including: alcohol content, extract, free amino nitrogen, sugars, acidity, colour, and the profile of volatile compounds and metal ions. The use of enzymes caused an increase in alcohol and fusel alcohols concentration in beers obtained. Total acidity, free amine nitrogen content, colour and sugar content indicated that the tested non-Saccharomyces yeast allowed obtaining beers with the proper analytical parameters.

The study dealt with quantitative and qualitative analysis of yeast microbiota found during spontaneous fermentation of grape musts from the white grape varieties Hibernal, Bianca and Seyval Blanc. Yeast strains were differentiated by random amplification of polymorphic DNA and pre-identified by restriction fragment length polymorphism of the 5.8S-ITS rRNA gene region. Final identification was obtained by 5.8S-ITS rRNA gene region sequencing. Metschnikowia pulcherrima, Hanseniaspora uvarum, Saccharomyces cerevisiae, Zygoascus meyerae, Wickerhamomyces anomalus and Kluyveromyces lactis strains were identified in all fermented musts. Higher yeast counts were determined in fresh musts from 2012 season compared to 2013, which directly affected their quantitative composition during the process. Musts obtained from the grapes from the Spotkaniówka vineyard were characterized by a higher microbial content compared to those obtained from the Srebrna Góra vineyard. It could be related to the microclimatic conditions in the vineyard. The grape varieties currently grown in Poland are characteristic for the cool climate region. Detailed studies on the microbiota of grapes and grape must allow for identification of yeast strains characteristic for a specific terroir and defining the 'identity' of a regional wine. [ABSTRACT FROM AUTHOR]

This paper concerns the dynamical modeling of the microbiological processes that occur in the biofilms that are formed on fine inert particles. Such biofilm forms e.g. in fluidized-bed bio-reactors, expanded bed biofilm reactors and biofilm air-lift suspension reactors. An approximate model that is based on the Laplace–Carson transform and a family of approximate models that are based on the concept of the pseudo-stationary substrate concentration profile in the biofilm were proposed. The applicability of the models to the microbiological processes was evaluated following Monod or Haldane kinetics in the conditions of dynamical biofilm growth. The use of approximate models significantly simplifies the computations compared to the exact one. Moreover, the stiffness that was present in the exact model, which was solved numerically by the method of lines, was eliminated. Good accuracy was obtained even for large internal mass transfer resistances in the biofilm. It was shown that significantly higher accuracy was obtained using one of the proposed models than that which was obtained using the previously published approximate model that was derived using the homotopy analysis method. [ABSTRACT FROM AUTHOR]