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Unlike majority of sorts of alcoholic drinks beer is considered significantly un-stable. This thesis examines the factors influencing the stability of beer, especially phys-ical-chemical, primarily content of polyphenols and potential of components of beer to form haze. Twenty eight samples from differently large breweries were processed (Černá Hora, Poutník Pelhřimov, Pegas, Richard and minibrewery of Mendel University in Brno). The total content of polyphenols was determined using the Folin-Ciocalteu method (spectrophotometrically at 750 nm) and subsequently expressed in the content of ferulic acid, which served as a standard for purposes of this study. The average con-tent of polyphenols was in Černá Hora Sklepní 338,5 mg.l-1, in light lager beer Poutník 370 mg.l-1, in light lager beer Pegas 694,5 mg.l-1, in light lager beer Richard 726,3 mg.l-1, in wheat beer from Mendel University in Brno 562 mg.l-1 and in Rauch from Mendel University in Brno 817 mg.l-1. Turbidity of beer for consumption and potential of beer components to form haze using EBC test was also assessed. Both types of turbidity were measured by turbi-dimeter at 620 nm using Helm BaSO4 standard and based on the measured values were compared with the established range of haze. Finally, the results were discussed and assessed physical-chemical stability of observed beers.

The aim of this diploma thesis is to explore the aspects of gushing in malt house Bernard. The main focus of the theoretical part is on a description of production of malt and beer, the history of gushing and an overview of current information about problematics of over foaming. The practical part is divided into free parts. In the first part I monitored a gushing potential of malt produced in 2015 and 2016 in the malt house Bernard. In the second part I dealt with a connection of particular technological parts of malt production and an evolution of gushing potential of intermediates day after day. In the third part there were investigated various modifications of Carlsberg test and their effect on the intensity of gushing. Also, I analysed the factors influencing the outcomes measured in the same samples in the malt house and in the laboratory of a Research Institute of Brewing and Malting in Brno.

Presented diploma thesis is about malting barley as a initial ingredient for producing beer and about its negative effect called gushing. In the first part of dissertation is described technological procedure of malt production and defined term gushing. Also there are mentioned information about cause of initiation, reduction possibilities and methods to describe gushing phenomena. Practical part is mainly focused to define susceptibility of malting barley to gushing and for testing was chosen three days test Carlsberg. The gushing was monitored on differently treated vegetation of spring barley which was grown in seasons 2012 and 2013 in Hrubčice locality. On the performed 160 testing samples were evaluated influence of threads barley on degree of barley gushing.

In theoretical part of this diploma thesis "Study of beer gushing using malts from Bernard's malthouse" are introduced elemental theoretical information about barley, malting and beer making. Further description of fungi, which can infect barley, and their products - mycotoxins and hydrophobins, which can contaminate malt. Next chapter is about gushing in general, sortinting of gushing, principle and factors what influence him, also about possibillities of reduction and prediction. Practical part of diploma thesis is about measuring gushing pontencial by Carlsberg test and is divided into two parts. Aim of first part is gushing pontecional of each interrmediate product during malting in Malthouse Rajhrad. Second part is focused on/at? optimalization prediction method called Carlsberg test and factors whitch can have influence onto method's results.

Le giclage de la bière est un phénomène de surmoussage qui a lieu lors de l’ouverture de la bouteille. Ce phénomène va être dépendant des conditions de développement du grain d’orge, la matière première de la bière, et notamment des conditions climatiques. Ces dernières années, le phénomène est observé de manière plus fréquente, et les techniques actuelles, comme la méthode Carlsberg, ne prédisent qu’un risque potentiel de giclage de la matière première avec une importante incertitude. Un test de criblage rapide de la matière première permettant l’identification de facteurs responsables du giclage est donc primordiale pour détecter précocement le risque de ce phénomène. Néanmoins, un manque d’informations et de recul sur les composés impliqués dans le giclage limite le développement de méthodes de prédiction rapide du risque. L’objectif principal de cette étude est d’identifier un ou des composés pouvant être à l’origine du phénomène de giclage de la bière. L’étude a été réalisée sur différents malts industriels présentant un risque giclage ou non et des orges artificiellement contaminées par des moisissures. Les extraits de malt obtenus sont des mélanges éminemment complexes. Ils ont été fractionnés par des procédés appropriés selon les propriétés de leurs constituants : par la taille, les propriétés moussantes et l’hydrophobie. Une réduction de la complexité de l’extrait a été nécessaire et obtenue par des techniques de séparation membranaire. Néanmoins, les macromolécules tels les glucides, les protéines et les polyphénols n’ont pas pu être isolés par ce procédé. La séparation par chromatographie de phase inverse a permis d’obtenir de bonnes informations sur la diversité des protéines présentes dans l’extrait mais l’analyse du potentiel giclage en aval reste limitée. Pour simuler des conditions réelles « comme au champ », une contamination artificielle de l’orge suivie d’une extraction en surface ont été réalisées. Le potentiel giclage des molécules issues de cette extraction a ensuite été analysé. Une purification de phase inverse a permis d’isoler une fraction concentrant les propriétés giclantes. Cette fraction contient des protéines très hydrophobes qui semblent être impliquées dans le giclage. L’identification des protéines après séparation en gel bidimensionnel a montré que ces protéines proviennent de la moisissure. Une protéine avec des propriétés proches des hydrophobines (hydrophobie et taille comparables) appelée Epl 1 a été identifiée et pourrait être un bon candidat responsable du giclage de la bière. En conclusion, la méthodologie développée dans la thèse a permis d’acquérir une meilleure connaissance des composés produits par les moisissures en surface d’orge et est applicable à d’autres orges contaminées ainsi qu’à du malt industriel / Beer gushing is an explosive over-generation of foam following the opening of a bottle. It is highly dependent on barley growing and harvesting climatic conditions and has been observed more frequently over the past years. Current technics, such as the modified Carlsberg test, only provide informations on a predictive gushing potential of malt with a large uncertainty. A rapid screening test on raw material leading to the identification of actual factor(s) responsible for the gushing is consequently highly required by the brewing industry. But a lack of informations about the compounds involved in gushing limits the development of such a technic. The initial goal of this study was to identify the compounds involved in beer gushing. This approach has been applied to industrial malts presenting gushing potential or not and artificially contaminated barleys in order to set a procedure to isolate compounds which may trigger gushing. In a first time, malt extracts, which are complex mixtures, have been produced and fractionated according to the properties of compounds such as their size, their foaming capacity or hydrophobicity. A good reduction of complexity of sample has been obtained after membrane filtration. Nevertheless, compounds like carbohydrates, proteins and polyphenols could not have been separated. Besides, separation by hydrophobicity has provided good information about the diversity of proteins but the analysis of their gushing potential remains difficult. Afterwards, in order to investigate the production of compounds by fungus at the surface of barley simulating real field crop production conditions, an artificial contamination was achieved and surface extraction with ultrapure water has been performed. Extracted molecules have been screened for their gushing activity. Thus, a purification of molecules by reverse phase chromatography allowed to isolate a gushing fraction from the surface extract. This fraction, which concentrates the gushing properties, is composed by proteins with high hydrophobicity which may be involved in gushing. This fraction was analyzed more in depth with a 2DE, and led to the identification of proteins all produced by fungus family. Among them, a protein called Epl1 appears to be of interest and could be a good candidate thanks its properties closed to hydrophobins (size and hydrophobicity). In conclusion, this methodology is developed to acquire a better knowledge about compounds produced by fungi at the surface of barley as well as to some industrial malt