Influence of the hopping technology on the storage-induced appearance of staling aldehydes in beer

J. Inst. Brew. 116(4), 381-398, 2010 In this paper, the involvement of iso-alpha-acids in the appearance of stale flavour in beer during storage was examined. Flavour instability upon storage, by far the most important quality problem of beer, may be caused by a multitude of reactions, in particular, the degradation of trans-iso-alpha-acids is pivotal. In order to gain improved understanding of the beer ageing process, the behaviour of the stereoisomers of the bitter acids was studied for the first time in pilot beers at particularly high and low proportions of the trans-iso-alpha-acids concentration relative to the cis-iso-alpha-acids concentration. Therefore, pure trans- respectively cis-isomers were required and obtained on a pilot scale by the separation of trans-iso-alpha-acids as beta-cyclodextrin inclusion complexes from a commercial isomerised hop extract, permitting the quantitative dosage to beer in mg/L amounts. The relationship between the storage-induced degradation of these iso-alpha-acids in authentic beer samples and the increase in staling aldehydes, especially 2-methylpropanal, 2-methylbutanal and 3-methylbutanal, is the subject of further investigations. A remarkable increase in the relative concentration of cis-iso-alpha-acids was observed in the beers bittered with purified trans-iso-alpha-acids, which may be ascribed to partial conversion, i.e., reverse isomerisation, of trans-iso-alpha-acids via alpha-acids into cis-iso-alpha-acids. In spite of the trans-specific degradation observed during ageing, the decomposition of these bitter acids leading to volatile carbonyl compounds is of minor importance. Aldehyde formation as a function of forced ageing was irrespective of the mode of bittering, emphasising that malt quality and the brewing process itself are probably the most important factors regarding the flavour instability of beer

Analytical and sensory assessment of hoppy aroma and bitterness of conventionally hopped and advanced hopped pilsner beers

J. Inst. Brew. 116(4), 445-458, 2010 Analytical and sensory aspects of hoppy aroma of conventionally hopped and advanced hopped pilot Pilsner beers were investigated. Linalool and several sesquiterpenoids were used as analytical markers for the hoppy aroma of the beers. Levels of linalool and sesquiterpenoids in the fresh beers, as well as sensory characteristics of hoppy aroma (intensity and attributed aroma descriptor(s)) clearly depended on the applied hop aromatisation technology and on the type of hop oil fraction used in advanced hopping. The most pronounced hoppy aroma was observed for the advanced bittered beers, either aromatised post-fermentation using a polar hop essence or at the end of wort boiling using pellets (late-hopping). However, all refined hop oil fractions used in this study for advanced aromatisation clearly affected the hoppy aroma impression. Analytical data on staling indicators, combined with sensory evaluations, further suggest that hop oil preparations may also affect flavour stability of the resulting beers in a positive way. In general, it can be concluded that hop aromatisation, whether performed in the advanced or conventional way, appears to mask beer staling, as demonstrated by lower overall sensory ageing scores

Green Malt for a Green Future – Feasibility and Challenges of Brewing Using Freshly Germinated (Unkilned) Malt: A Review

In malting, the kilning step is by far the dominant user of energy and has thus become the main target in reducing the carbon footprint of malting operations. Brewing beer using ‘green’ (germinated, but not dried) malt, thus saving the substantial energy input associated with kilning and conserving the water contained in the green malt, could improve the energy and water efficiency of malting operations. Furthermore, the high enzyme complement in green malt could enable more efficient brewing using unmalted cereals (e.g. raw barley) to create highly attenuated beers, without the use of exogenous enzymes. The objective of this review is to unravel the major advantages, but also quality and technical challenges, which could serve as a base for future studies on successfully brewing with green malt. Furthermore, the aim is to evaluate the impacts of such a process on beer flavour and flavour (in)stability. This is important to establish because one can make arguments that such a process will either improve flavour stability (reduced heat load should reduce the pool of staling aldehydes) or worsen it (since lipoxygenase activity and dimethyl sulphide potential can be regulated by heat treatment during kilning)

Exploring aldehyde release in beer by 4-vinylpyridine and the effect of cysteine addition on the beer's pool of bound aldehydes

As a continuation of our previous work, which concerned the binding of aldehydes to bisulfite and cysteine, this article presents more results on the applicability of 4-vinylpyridine addition to beer prior to analysis aiming at release of aldehydes from these preformed bound states, thus making them quantifiable with the headspace solid-phase microextraction method combined with gas chromatography-mass spectrometry. This article also presents the first results on spiking beer samples with cysteine prior to forced-aging, pointing to the important role of cysteine in beer flavor stability. Both the levels in free and bound aldehydes show a relatively large degree of variation among different beers, but also between marker aldehydes. For some aldehydes (e.g., hexanal), the bound amount was shown to increase rather strongly upon forced beer aging, whereas for others (e.g., 2-methylpropanal), large amounts appeared to already be present in a bound state in the fresh samples. Spiking beer samples with cysteine prior to aging significantly lowered the aldehyde levels compared with nonspiked samples. Flavor stability of the cysteine-spiked beers was thereby greatly improved through aldehyde-cysteine adduct formation. It was further hypothesized that, in addition to efficient binding of aldehydes, cysteine also inhibits the formation of furfural during beer aging from Maillard reaction intermediates

Microwave-assisted production of biodiesel

ncreasing popularity of sour beer urges the development of novel solutions for controlled fermentations both for fast acidification and consistency in product flavor and quality. One possible approach is the use of Saccharomyces cerevisiae in co-fermentation with Lactobacillus species, which produce lactic acid as a major end-product of carbohydrate catabolism. The ability of lactobacilli to ferment beer is determined by their capacity to sustain brewing-related stresses, including hop iso-α acids, low pH and ethanol. Here, we evaluated the tolerance of Lactobacillus brevis BSO464 and Lactobacillus buchneri CD034 to beer conditions and different fermentation strategies as well as their use in the brewing process in mixed fermentation with a brewer’s yeast, S. cerevisiae US-05. Results were compared with those obtained with a commercial Lactobacillus plantarum (WildBrewTM Sour Pitch), a strain commonly used for kettle souring. In pure cultures, the three strains showed varying susceptibility to stresses, with L. brevis being the most resistant and L. plantarum displaying the lowest stress tolerance. When in co-fermentation with S. cerevisiae, both L. plantarum and L. brevis were able to generate sour beer in as little as 21 days, and their presence positively influenced the composition of flavor-active compounds. Both sour beers were sensorially different from each other and from a reference beer fermented by S. cerevisiae alone. While the beer produced with L. plantarum had an increased intensity in fruity odor and dried fruit odor, the L. brevis beer had a higher total flavor intensity, acidic taste and astringency. Remarkably, the beer generated with L. brevis was perceived as comparable to a commercial sour beer in multiple sensory attributes. Taken together, this study demonstrates the feasibility of using L. brevis BSO464 and L. plantarum in co-fermentation with S. cerevisiae for controlled sour beer production with shortened production time.publishedVersio

Brewing with 100% green malt – process development and key quality indicators

Brewing with undried, germinated (green) malt has the potential to lower energy and water usage in the malting and brewing chain. However, doing so introduces technical and biochemical (flavour) challenges. Beers were brewed using 100% green malt (n = 3) or kilned pilsner malt (n = 3), prepared from the same batch in each case, utilising the pilot brewery at KU Leuven (2.5 hL). Three further pairs of beers were brewed whereby the green malt was pre‐steeped under deaerated water for 1 hour; this procedure was previously shown to lower LOX activity in green malt. Six green malt beers were brewed with acceptable specifications in terms of pH, alcohol content, foam stability and colour. No significant taints or obvious defects were detected in green malt beers. Increased S‐methyl methionine levels were measured in worts and beers made from green malt, however DMS concentrations in the finished beers did not differ significantly from the reference beers. Furthermore, the results demonstrated promising indicators for flavour stability, such as reduced TBI, lower residual FAN and trihydroxy fatty acid (THFA) levels in brews using untreated green malt. Using re‐steep water in green malt brewing (for reasons of water economy), however, increased THFA levels, possibly because oxygen uptake was not adequately controlled at this step. Whilst further process optimisations are undoubtedly required, it is shown that an acceptable lager style beer could be brewed to a specification not dissimilar to that of a kilned malt control beer, using 100% green malt with intact rootlets. © 2020 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distillin

On the contribution of malt quality and the malting process to the formation of beer staling aldehydes: a review

Despite decades of extensive research, beer flavour instability remains a challenge for both brewing and malting industries. Malt impacts the brewing process as well as the quality of the final beer. It also affects the stability of beer flavour, as it delivers to the brewing process various compounds with the potential to compromise the desired flavour characteristics of beer. These include staling aldehydes and their precursors, such as amino acids, reducing sugars, α-dicarbonyls and bound-state aldehydes. In general, the content of these compounds depends on barley variety and quality, the malting regime and final malt quality. Malt that represents a low potential for beer staling, i.e. that has low values of Kolbach Index, heat load, colour, LOX activity, Strecker aldehydes, transition metal ions and high antioxidative activity, leads to beer with enhanced flavour stability. However, the consistent production of malt with the desired quality remains challenging. Approaches to achieve this include adjustment of steeping and germination conditions, allowing control of grain modification and thus, the reservoir of aldehydes precursors. Also, the application of alternative kilning technologies may reduce the applied heat load, responsible for the formation of staling aldehydes and triggering development of the oxidising free radical species. This review provides an evaluation of current knowledge on the contribution of the malting process and malt quality to the formation of beer staling aldehydes. © 2021 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling

Early protein flocculation to decrease boiling need of wort

status: accepte

System Changes in Wort Production for the Improvement of the Flavour Stability of Lager Beer

The objective of the research project is to study the impact of an innovative wort production method on flavour quality and flavour stability of lager beer. The innovation comprises 1) thick and fast mashing under anti-oxidative conditions to save time and energy; 2) high mashing-off temperature (95°C) compared to conventional mashing-off temperature of 78°C; 3) acidified sparging; and 4) in-line wort stripping with culinary steam and in-kettle stripping during filling of the kettle (till kettle is full) for continuously stripping of unwanted volatiles. After wort filtration and in-line stripping, no additional boiling is required. Special attention was paid to mashing-in conditions (O2, pH, temperature), in order to prevent early oxidation. During transfer of the mash to the mash vessel, the malt aldehydes are to be stripped off as much as possible. Clean steam injectors in combination with over-sized chimneys and condensate traps and high mashing-off temperatures should facilitate the release and stripping of unwanted volatile aldehydes. Mashing-off at temperatures above 95°C has three aims: 1. strip off unwanted volatile aldehydes; 2. partially degrade of SMM to DMS (flavour of Brussels sprouts); 3. coagulate and flocculate high molecular weight proteins. The holding time of the elevated mashing-off temperature will depend on these three items.The fastest and thickest mashing conditions were first evaluated to produce concentrated mashes in the shortest time frame. A thick mash results in smaller total volumes so that low water and reduced energy input is required during mashing. An efficient sparging will then lead to lowest volumes for boiling with highest extract content which is again beneficial in view of energy consumption and brewhouse capacity. Fine milling in combination with thinbed wort filtration resulted in highly comparable wort, beer, and ageing profiles compared to conventional coarse milling/lautertun operations. High mashing-off temperature resulted in a fast wort filtration, bright sweet wort and a low heat load (based on the TB-Index). Due to the high mashing-off and wort filtration temperature, SMM is already transformed into free DMS which evaporates partially at mashing-off. Sufficient conversion of SMM and removal of DMS is possible by in-line and in-kettle clean steam injection during filling of the combination vessel. Sparging with acidified water at high temperature minimised the extraction of extra proanthocyanidins during the sparging step ending up with comparable amounts compared to conventional wort production. High mashing-off temperature also resulted in decreased levels of haze sensitive proteins, in comparison with conventional mashing-off temperature. The use of steam to form and strip DMS however results in the formation of a low trub content, but the small protein flocks are difficult to remove. No striking differences have been found when comparing conventionally produced beers with the innovative beers. However, important differences have been observed when the beers were subjected to ageing. Due to the acidified sparging, high aldehyde contents have been found in the pitching wort upon innovative wort production. The low pH of sparging liquor seems to result in an enhanced release of imine-bound aldehydes. As apparent from analysis of pitching wort, these free aldehydes have not been efficiently stripped off (in contrast to DMS), but after fermentation, comparable levels of free aldehydes were found in the fresh beers. However, during ageing of the innovative beer, lower levels of aldehydes were found resulting in significantly lower overall ageing sensory scores. The release of aldehydes during acidified sparging, even at conventional sparge temperatures of 78°C, is also malt dependent. In conclusion, the innovative wort production, executed in less than 3.5 hours, results in a highly comparable fresh beer, but with an extended flavour stability compared to conventional beer production. Concentrated mashes and highest extract content due to low sparge rates will result in a decreased need of energy for wort production. The high throughput of the two vessel brewhouse with a thinbed filter will also reduce the investment cost.TABLE OF CONTENTS LIST OF ABBREVIATIONS AND SYMBOLS ix CONTEXT AND AIMS OF THIS STUDY xi CHAPTER I. WORT PRODUCTION: A REVIEW 1 I.1. Introduction to the conventional wort production 2 I.2. Milling and mashing 3 I.2.1. Impact of milling and mashing on wort quality 3 I.2.2. Fine milling technology 7 I.3. Lautering 9 I.3.1. The impact of milling and mashing on the lauter performance 9 I.3.2. Filter cycle in case of membrane assisted thinbed filter operations 13 I.4. Boiling 16 I.4.1. Introduction 16 I.4.2. Critical comments with regard to conventional wort boiling 17 I.4.3. Importance of the construction of a boiling kettle 19 I.4.4. Conventional Boiling systems 19 I.4.5.Wort ‘boiling’ with extra stripping 23 I.4.6. Advanced boiling systems 27 I.5. Relation between wort production and beer flavour stability 29 CHAPTER II. THE INFLUENCE OF VERY THICK AND FAST MASHING CONDITIONS ON THE WORT COMPOSITION 39 II.1. Introduction 40 II.2 Materials and Methods 40 II.2.1. Malt 40 II.2.2. Wort production at lab scale 41 II.2.3. Beer production 42 II.2.4. Wort analyses 42 II. 3. Results and discussions 45 II.3.1. Influence of milling, mashing-in temperature and pH on attenuation limit and FAN levels 45 II.3.2. Effect of mash thickness and short mashing programs on the extract yield, AAL, FAN levels and sugar composition 53 II.4 Conclusion 64 CHAPTER III. THE IMPACT OF WORT PRODUCTION ON THE FLAVOUR QUALITY AND STABILITY OF PALE LAGER BEER 65 III.1 Introduction 66 III.2. Materials and Methods 66 III.2.1. Conventional wort production - coarse milling (CM) 66 III.2.2. Conventional wort production - fine milling (FM) 67 III.2.3. Analyses 67 III. 3 Results and discussions 70 III.3.1. Brewing performance 71 III.3.2. Comparison of pitching wort 72 III.3.3. Comparison of fresh beers 76 III.3.4. Comparison of beer ageing 79 III.4 Conclusion 81 CHAPTER IV. SUFFICIENT FORMATION AND REMOVAL OF DMS WITHOUT CONVENTIONAL BOILING 83 IV.1 Introduction 84 IV.2. Materials and Methods 84 IV.2.1. Conventional wort production – coarse milling 84 IV.2.2. Conventional wort production – fine milling 85 IV.2.3. Innovative wort production 85 IV.2.4. Headspace SPME GC-PFPD analysis of DMS and DMS precursor in wort and beer 85 IV.2.5. Gas chromatographic analysis of trihydroxy fatty acids 86 IV.3 Results and discussions 86 IV.3.1. Determination of DMS 86 IV.3.2. Determination of DMS precursor 87 IV.3.3. The influence of milling on DMS formation and evaporation in conventional brewing trials 89 IV.3.4. DMS formation and evaporation during innovative brewing trials 92 IV.4 Conclusion 96 CHAPTER V. IMPACT OF HIGH MASHING-OFF TEMPERATURE ON LAUTER PERFORMANCE AND WORT COMPOSITION 99 V.1. Introduction 100 V.2. Materials and Methods 101 V.2.1. Conventional wort production - fine milling 101 V.2.2. Innovative wort production 101 V.2.3. Innovative wort production with additions to improve protein flocculation 101 V.2.4. Analyses 101 V.3. Results and discussions 102 V.3.1. Influence of high mashing-off temperature on wort composition 102 V.3.2. Improved protein flocculation and hot wort clarification 108 V.3.3. Evaluation of final beer quality 110 V.3.4. Energy consequences of mashing-off at 95°C 113 V.4. Conclusion 114 CHAPTER VI. PROLONGED BEER FLAVOUR STABILITY BY IMPLEMENTATION OH HIGH TEMPERATURE MASHING-OFF AND ACIDIFIED SPARGING 115 VI.1 Introduction 116 VI.2 Materials and Methods 116 VI.2.1. Conventional wort production - fine milling 116 VI.2.2. Innovative wort production 117 VI.2.3. Analyses 117 VI.3 Results and discussions 117 VI.3.1. Analysis of first wort 118 VI.3.2. Analysis of pitching wort 119 VI.3.3. Analysis of fresh beer 122 VI.3.4. Analysis of aged beer 124 VI.4 Conclusion 127 CHAPTER VII. GENERAL CONCLUSIONS AND FUTURE PERSPECTIVES 129 VII.1. General conclusions 130 VII.2. Future perspectives 135 References I Publication list XIXstatus: publishe

System changes to extend flavour stability

status: accepte