The use of reduced iso-alpha-acids in brewing has become more widespread in past years, although their characteristics during beer ageing are not completely known. During our investigations, important differences in ageing characteristics were detected not only between the categories of reduced and non-reduced hop extracts, but also within the group of beers containing reduced hop products. Forced ageing in the absence of light had the strongest impact on beers hopped with CO2-extract, followed by iso-alpha-extracts. Rho, Tetra and Hexa showed a significantly better stability with the tendency to improve from Rho- over Tetra- to Hexahydro-isohumulone. Under light exposure, besides showing lightstruck flavour, beers hopped with CO2-extract were the first to show cardboardy oxidation aroma, while beers containing only reduced hop products were virtually unaffected. Extended periods of light exposure, however, led to the formation of methyl-furfuryl-disulphide (MFDS) off-flavour, also in light-stable beers, as previously reported [1]. The findings from sensory analysis could he confirmed by instrumental analysis of chemiluminescence behaviour. The results indicate clearly that the choice of hop products has a decisive influence on beer flavour stability.

The lipoxygenase isoenzymes LOX1 and LOX2 from green malt were separated by isoelectric focusing, and their catalytic properties regarding complex lipids as substrates were characterized. The regio- and stereoisomers of hydroperoxy octadecadienoates (HPODE) resulting from LOX1 and LOX2 enzymatic transformations of linoleic acid, methyl linoleate, linoleic acid glycerol esters monolinolein, dilinolein, and trilinolein, and 1-palmitoyl-2-linoleoyl-glycero-3-phosphocholine (PamLinGroPCho) were determined. In addition, biotransformations of polar and nonpolar lipids extracted from malt were performed with LOX1 and LOX2. The results show that LOX2 catalyzes the oxidation of esterified fatty acids at a higher rate and is more regioselective than LOX1. The dual position specificity of LOX2 (9-HPODE:13-HPODE) with trilinolein as the substrate (6:94) was higher than the resultant ratio (13:87) when free linoleic acid was transformed. A high (S)-enantiomeric excess of 13-HPODE was analyzed with all esterified substrates confirming the formation of 13-HPODE through the LOX2 enzyme; however, 9-HPODE detected after LOX2 biotransformations showed (R)-enantiomeric excesses. PamLinGroPCho was oxygenated by LOX1 with the highest regio- and stereoselectivities among the applied substrates.

The characterisation of lipoxygenases LOX1 and LOX2 and hydroperoxyoctadecadienoic acid (HPODE) degrading enzymes from barley green malt is reported. Hydroxylapatite chromatography (HAC) and isoelectric focussing (IEF) were performed to separate and purify LOX isoenzymes. The regio- and stereoselectivity of LOX1 and LOX2 towards linoleic acid as substrate was characterised. HAC purified isoenzyme LOX1 showed a 9-HPODE:13-HPODE ratio of 75:25 and LOX2 a ratio of 39:61. IEF separated LOX1 and LOX2 transformed linoleic acid to 9-:13-HPODE ratios of 90:10, and 13:87, respectively. 9-HPODE stereoisomers from LOX1 exhibited a S:R ratio of 93:7 and 13-HPODE from LOX2 a S:R ratio of 89:11. However, the minor regioisomers were analysed with S:R = 48:52 (LOX1, 13-HPODE) and 40:60 (LOX2, 9-HPODE). These results indicate a complete LOX isoenzyme separation by IEF. Hydroperoxide-metabolising enzymes, which were investigated in the IEF fractions, did not interfere with the dual position specificities of LOX isoenzymes.

La determination du comportement de floculation des levures de brasserie represente un aspect important pour l'assurance qualite a l'interieur d'une entreprise. Un changement dans le pouvoir floculent exerce une influence directe sur le deroulement de la fermentation, de la filtrabilite de la biere et sur la qualite de la biere. On a teste trois methodes de laboratoire de determination de la floculation des levures pour une application pratique. Pour la comparaison on a utilise des fermentations paralleles dans des tubes EBC et tanks cylindre-coniques en acier inoxydable. Les methodes appropriees etaient la determination de l'hydrophobicite de la surface cellulaire d'apres Akiyama-Jibiki et le test modifie de Helm suivant d'Hautcourt et Smart. En utilisant les deux methodes, il etait possible d'evaluerrapidement et facon sure, le comportement de floculence. Le test modifie de Helm par Mota et Soares etait moins approprie car il presentait des incertitudes plus importantes.

Within an experiment concerning the influence of barley and malt storage on their general quality and lipid oxidation in particular different spring and winter barley varieties of the crops 1999 and 2000 were processed. In addition to malting the barleys the produced malts were also used for brewing purposes. The flavour stability of the resulting beers was evaluated by a trained taste panel by comparing the fresh ones with those that were stored for four weeks at 28 degreesC. Five different raw material batches were analysed: Fresh barley and malt, barley and malt stored for six months and malt produced from barley which has been stored for six months. Three different beers have been produced using these five batches: Beer from fresh malt, beer from a half year stored malt and beer from malt which was produced from stored barley. It could be shown that there is only a slight influence of a suitable six month storage period of the raw materials on their standard parameters: Only the moisture content of the raw materials of all three batches increases slightly (respiration, hygroscopicity etc.) and the proteolysis of the malts produced from stored barleys was a little bit more intensive than that produced from the fresh ones. The flavour stability of the beers produced from stored raw materials was not found to be worse than that produced from fresh barley resp. malt although the amount of free and triglyceride-bonded hydroxy fatty acids, especially trihydroxy fatty acids (THOE), was noticeable influenced by the storage period. In particular the THOE of barley and malt could be a suitable marker for ageing processes on the base of lipid oxidation.

Although immobilised main fermentation has clear advantages, insufficient long-term stability of product quality is the main reason that it is still awaiting its breakthrough. Therefore immobilised main fermentations in pilot scale with varying reactor types, carrier materials and aeration rates were applied in order to evaluate measures to improve long-term stability. A comprehensive set of data including beer analyses, taste testing and analyses of yeast vitality during fermentation was collected. It is shown that long term stability is manageable, and a toolset of technological measures is presented to overcome the existing limitations of this technology.

The determination of the flocculation behaviour of brewers' yeast represents an important part of brewery quality management, because alterations of this characteristic yeast property will directly influence the fermentation process, filterability of beer, and final beer quality. In this research work, three laboratory methods for measuring yeast flocculation were tested and evaluated. As a comparison, we simultaneously conducted fermentation trials in EBC-Fermentation Test Tubes and stainless steel CCTs. Both the determination of cell surface hydrophobicity according to Akiyama-Jibiki and the modified Helm's Test according to D'Hautcourt und Smart were practical and reliable methods, which therefore can be recommended. As a result of our findings, the modified Helm's Test according to Mota und Soares was less suitable because of its partly inaccurate results.

In a previous report from the same authors it was shown that the major part of hydroxy fatty acids is esterified as triacylglycerols in barley and malt. Moreover in most of the analysed samples a maximum of oxidized linoleic acid substances was found in barley and not in the corresponding malt. Examination of four different barley varieties concerning the evolution of mentioned stale flavour precursor during malting indicates a rapid increase of their concentration during germination with a maximum at the fifth or sixth day. A longer germination period leads to a lower content of all esterified hydroxy fatty acids in most cases. During withering a strong decrease of the level of oxygenated fatty acids can be detected, followed by an increase at the kilning process again. Comparison of three different kilning temperatures, in particular 70 degreesC, 85 degreesC and 100 degreesC gives lowest values of THOE at 85 degreesC. Variation of other malting parameters, e.g. germination time and temperature or steeping degree gives a considerable change in hydroxy fatty acid concentration, but an optimal malting procedure leading to low amounts of especially THOE, for all barley varieties, cannot be given yet.

L'oxydation de l'acide linoleique semble etre le mecanisme de reaction le plus important pour la formation des precurseurs des carbonyles de vieillissement actifs sur le plan sensoriel, par exemple le (E)-2- nonenal connu dans la biere. Sur cette base, il est usuel dans la recherche brassicole, de doser les acides gras hydroxyles libres a tous les stades de la fabrication de la biere dans le but de pouvoir tirer des conclusions sur le comportement de vieillissement du produit fini. A l'aide d'une nouvelle methode d'analyse il a ete possible, pour la premiere fois, de demontrer qu'une partie importante des acides gras hydroxyles etaient deja presents dans l'orge et dans le malt, ceci sous forme de triacylgycerols esterifies. A l'aide de cette methode de mesure, huit groupes de substances de l'acide linoleique oxyde ont ete identifies par CPG/SM : deux acides monohydroxyoctadecadieniques (HOD), deux acides dihydroxyoctadeceniques (DHOE) et quatre acides trihydroxyoctadeceniques (THOE). L'examen de plus de vingt orges commerciales et des malts fabriques a partir de ces orges a montre que dans la majorite des cas, un maximum d'acides gras hydroxyles lies aux triglycerides etaient deja presents dans l'orge. La repartition moyenne dans l'orge et le malt des differents groupes est la suivante : 50 % HOD, 30 % DHOE et 20 % THOE. En liaison avec les domaines de concentration des acides gras hydroxyles on a trouve des valeurs de 50 ppm jusqu'a 110 ppm HOD, 20 ppm jusqu'a 90 ppm DHOE et 10 ppm jusqu'a 65 ppm THOE sur matiere seche dans les matieres premieres brassicoles. De plus on a trouve une forte influence des parametres variete, provenance et annee sur la quantite des precurseurs possibles des flaveurs de vieillissement.

The oxidation of linolic acid appears to be one of the most significant reaction mechanisms for the development of first forerunner taste active aging carbonyl such as, for example, the known (E)-2-nonenal. in beer. As a result of this it has been usual practice for some time now in scientific brewery research to measure the free given hydroxy fatty acids in all possible stages when producing beer to be able in this way to come to possible conclusions as to the aging behaviour of the finished product. With the help of a unique method of analysis it has now been possible to evidence for the first time that a considerable proportion of hydroxy fatty acids are already in barley and malt and namely esterfied in the to of triacylglycerole. By means of this analytical measurement it is possible to evidence eight groups of substances in oxidised linolic acid through the GUMS: two monohydroxyoctadecadecane acids (HOD), two dihydroxyoctadecane acids (DHOE) and four trihydroxyoctadecane acids (THOE). The study of over twenty commercial barleys and the malt made from these revealed that in the majority of cases a maximum of triglyceride-bonded hydroxy fatty acids are already to be found in the barley. Moreover the average distribution of the different groups reveals approx. 50% HOD, 30% DHOE and 20% THOE in barley and malt. As far as the concentration ranges of the esterfied hydroxy fatty acids to be found in the dry substance of the brewery raw materials are concerned these were values from 50 ppm to 110 ppm HOD, 20 ppm to 90 ppm DHOE and 10 ppm to 65 ppm THOE. Over and above this it A as found that the variety, provenience and year parameters have a considerable influence on the quantity of this possible aging taste forerunner.

Based on the trials applied in the first part of this paper working with defined aeration and variation of carrier material in a fixed bed reactor, further tests were developed. Here in the main trial a loop reactor with silicon-carbide modules as an immobilization matrix, the so called MPI-reactor, was used for immo-main fermentation. In the first time effects which were known from former trials like pH-increase, reduced synthesis of higher alcohols and minimized FAN-consumption were found. These developments were slightly retarded in the MPI-reactor in comparison to fixed bed reactor. After 25 days the aeration rate was increased in order to counteract against the described changes of beer quality. After this in general it was possible to produce beers of a relatively constant quality over the reactor operation period of 92 days which could be proved by results of chemical-technical as well as sensory analysis. As expected a two-week interruption of reactor operation lead to a noticeably changed quality of the beer that remained in the reactor during this time. But after restarting the reactor it was possible to produce beer of the original quality within a few days. In preliminary tests the yeast was exposed to forced starvation. By this means expressiveness and practical feasibility of methods for the evaluation of yeast vitality were to be determined. The concentration of acid-soluble glycogen proved to be an expressive criterion. Also the intracellular pH-value appeared to be interesting, but it was not possible to give a final evaluation with the available results. The Acidification-Power-value shows correct tendencies but it suffers from its weak reproducibility. By none of the mentioned methods, which were applied in the main trial, too, a lasting and continous decline of yeast vitality could be shown during the long-term trial in the MPI-reactor. Also the determination of yeast viability from cell samples taken at the reactor outlet support these results.

Dans une precedente publication on a pu montrer qu'une importante partie des acides gras hydroxyles de l'orge et du malt se trouvait sous forme de triglycerides esterifies. Dans les echantillons d'orge examines on a en plus trouve une concentration en acides gras triglycerides oxygenes plus elevee que dans le malt correspondant. L'examen de quatre varietes d'orge differentes presentait une forte augmentation de la concentration en composes des potentiels des precurseurs du gout de vieillissement pendant le procede de germination avec un maximum au cinquieme ou sixieme jour de germination. Une germination plus longue conduisait, dans la majorite des cas, a une diminution des substances esterifiees mentionnees. Dans le cadre du fanage on a observe une forte diminution de toutes les classes d'acides gras hydroxyles, suivie d'une legere augmentation pendant le touraillage. La comparaison de trois temperatures de touraillage, c'est-a-dire, faible a 70°C, usuelle a 85 °C et elevee a 100 °C conduisait avec 85 °C a la concentration la plus faible pour les THOE (acides trihydroxyoctadeceniques). La variation d'autres parametres du maltage, par exemple la duree et la temperature de germination ou le degre de trempage conduisait a d'importantes variations dans la concentration des produits de l'acide linoleique oxyde. Toutefois on ne peut pas adapter pour toutes les varietes d'orge le meme diagramme de maltage qui conduit a de faibles quantites de THOE.

Pour un essai de faisabilite on a determine dans un reacteur a lit fixe avec de la cellulose DEAE les conditions d'experience pour l'aeration paraissant optimales dans le but d'ameliorer la stabilite de longue duree du reacteur. Des changements dans le debit d'aeration en une journee conduisait a des changements de la quantite et la composition des produits de fermentation formes. Dans un autre essai dans le lit fixe on a effectue l'aeration standard pendant toute la duree de l'experience et analyse de facon detaille la biere ainsi produite. En comparaison avec un essai de reference non aere, on a obtenu apres une duree du reacteur de 47 jours, une qualite de biere bien plus reguliere concernant les alcools superieurs aliphatiques et les esters. Il a pu etre toutefois tendentieux d'observe, egalement pour l'essai aere, une diminution de la consommation de l'azote amine libre (AAL) et d'une augmentation du pH. En plus la cellulose DEAE montrait une forte tendance de blocage ce qui conduit a la non-continuation des essais avec ce materiel. Dans une autre serie d'experiences on a compare le materiel de verre sinter avec un nouveau support en silicone, ces deux materiaux ont une similitude morphologique. Le taux d'immobilisation avec ce nouveau materiau etait plus faible compare au Siran® et l'absorption de composes amers etait plus elevee. Un grand avantage du support en silicone etait une grande stabilite mecanique. La repercussion des deux materiaux de support sur la qualite de la biere avec l'essai aere et non-aere pendant le deroulement du reacteur n'avait qu'une influence secondaire. L'aeration avait une plus grande influence que le materiel. On a observe dans ce cas un changement de la qualite de la biere dans la duree, de la meme facon que pour les essais aeres avec la cellulose DEAE. La tendance de blocage avec les deux materiaux etait moins importante qu'avec la cellulose DEAE.

Within a screening-test in a fixed bed reactor with DEAE-cellulose one aeration rate was determined that appeared to be Suitable for the chosen test conditions in order to improve the long term stability of the reactor operation by this means. Changes of the aeration rate had an effect on concentration and composition of fermentation by-products within one day. In a further fixed bed trial aeration was applied with the standard aeration-rate over the entire test period and the produced beer was analyzed comprehensively. Compared with an unaerated reference trial a considerably improved constance of beer quality concerning higher aliphatic alcohols and esters was found during the reactor operation period of 47 days. Nevertheless a tendency of reduced FAN-consumption and increased pH-value was found in the aerated trial, too. Furthermore DEAE-cellulose tended to clog and in consequence trials with this material were not continued. In an additional test series the sinterglass material SIRAN((R)) was compared with a novel carrier made of silicon, since both materials showed big similarities concerning their morphology. The immobilisation rate was smaller than that of SIRAN((R)) and more bittering substances were adsorbed by the new material, too. A great advantage of the silicon-carrier has been its good mechanical stability. During reactor operation in aerated and unaerated applications the influence of both carrier materials on beer quality was almost neglectable. Here the aeration had an considerably stronger influence than the used material. Like in the trials with DEAE-cellulose a slight change of beer quality was determinable in case of the aerated tests. On the other hand the tendency of clogging was lower for both materials in comparison to DEAE-cellulose.

Today the production of "alcohol-free" and alcohol-reduced beers is based mainly on the removal of alcohol after fermentation. Besides the diffusion of alcohol through suitable membranes, evaporation under vacuum has widely established itself on the market. Falling film evaporation seems to be the most advantageous evaporation technique available, since it combines simple plant construction with a high efficiency. Over the past years, several membrane systems for beer dealcoholisation have been installed, assumingly following a not always objectively founded trend to avoid any thermal stress on beer. Although membrane systems deliver quite satisfactory results in the majority of cases, this does not at all indicate that membrane-based alcohol removal was fundamentally superior to evaporation methods, or that it would in principle yield alcohol-free and alcohol-reduced beers of higher quality. There are indeed studies on the influence of falling film evaporation on the quality of "alcohol-free" and alcohol-reduced beers, but a comparison of the impact of various process engineering parameters has not been published until now. This paper systematically covers the advantages and disadvantages of different working methods in alcohol removal from beer by falling film evaporation.

At the present rime "alcohol-free" and low-alcohol beers are mainly produced by subsequent removal of the alcohol from partially or fully fermented beers. Alcohol diffusion through suitable membranes as well as evaporation under vacuum have become market-established methods. Dialysis has gained particular significance among membrane methods. All membrane systems for dealcoholisation of beer feature complete absence of thermal product stress. However, this does not automatically mean that membrane technologies are generally superior to alcohol evaporation and that they would on principle lead to low-alcohol and "alcohol-free" beers of higher quality. The paper to hand is a systematic review of the advantages and disadvantages of different working methods for the dealcoholisation of beer by means of dialysis. Indeed studies on the effects of dialysis on the quality of beer when producing low-alcohol and "alcohol-free" beers have already been published, but up until now no comparison has been made of the effects of the different process engineering parameters.

As is known the physical pressure, i. e. CO2 partial pressure apart from the fermenting temperature (1-3) and the osmotic pressure (4.5), has also an influence on the fermenting behaviour of yeast. The increased concentration or the carbon dioxide dissolved in the fermenting medium leads to strong impairment of the metabolism. In this case the energy metabolism is restricted to a considerably less extent. The practical application of this interrelation is to ferment under pressure at comparably high temperatures without the aroma components (for example, high alcohols) typical for a forced yeast propagation. On the other hand the effects of physical pressure on the yeast vitality have not been researched adequately at all up to now. In the studies it was revealed that the influence of different CO2 partial pressures on the glycogenous metabolism between the effect on the crop and pitching yeast is different. Primarily different CO2 partial pressures influence the glycogenous concentration of the crop yeast.

Trials on the impact of flash pasteurization on beer quality showed that higher pasteurization temperatures with shorter holding times are favourable for beer quality. However, the killing effect in the temperature range up to 90 degrees C has not been elucidated so far. Pasteurization temperatures of 50 degrees; 60 degrees; 72 degrees; 84 degrees and 90 degrees C and pasteurization units of 0; 15; 80 and 500 PU were used. The associated residence times were calculated according to Del Vecchio et al.'s formula. The experiments with beer-relevant yeasts and bacteria showed that Saccharomyces yeasts are much easier to inactivate than Lactobacilli and Pediococci. Furthermore, it can be stated that the commonly used PU calculation according to Del Vecchio reflects that actual killing characteristics in the temperature range from 60 degrees to 72 degrees C quite precisely. Although flash pasteurization with low PU figures at temperatures higher than 72 degrees C and with very high amounts of bacteria may be insufficient, because the real inactivation effect is lower than indicated, there is no need to increase the PU load when changing to higher pasteurization temperatures and shorter holding times in practical application.