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The growing group of health-conscious consumers drives the development and sales in the market of low- or non-alcoholic beverages. In particular, sales in alcohol-free beer (AFB) has drastically gained in recent years, giving the incentive to further advance alcohol-free products. This thesis comprises the development of a new technology to produce an alcohol-free beer with an improved flavour, that is, an AFB with a significantly lower concentration in Strecker aldehydes. Despite the fact that Strecker aldehydes are present at trace concentrations of a few micrograms per litre, these compounds are majorly associated with the characteristic wort offflavour in alcohol-free beer. In the first stage, the origin of wort flavours is elucidated, and furthermore, the impact of the changed production process in comparison to regular beer and its resulting changes in the product is discussed. The most significant pathways of origin are the Maillard reactions and Strecker degradation, however, many other formation pathways have been suggested. While alcohol-free beers produced through regular fermentation and subsequent dealcoholisation are generally low in wort off-flavour, biologically produced AFBs exhibit a rather strong wortiness. This is because yeast’s activity during the fermentation is restricted to prevent alcohol formation, having the side effect that other compounds such as aldehydes are not converted to neutral or characteristic beer flavours. As it is impossible to prevent the formation of wort flavour, selective removal is required to produce an alcohol-free beer with improved flavour profile (balance). Subsequently, technologies applied to remove aldehydes from aqueous streams are investigated. Mechanisms that can be exploited for such removal are various – from separation based on size or volatility (distillation, pervaporation or membrane filtration) through sorption or conversion – past research has nearly studied all removal techniques available for aldehydes. However, most of the available techniques are not selective enough for a complex matrix such as beer, or not suitable for the application in the food industry. Nonetheless, adsorption is identified as the most promising technique to facilitate selective aldehyde removal. As a benchmark system, a dealcoholisation plant (spinning cone column) is studied with special focus on wort flavour removal. While volatile aldehydes such as 3-methylbutanal can relatively easily be reduced, methional, having a high boiling point, is not sufficiently separated from the end-product. Furthermore, due to the impact of heat, and ergo, the continuous formation and evaporation of these flavours, a plateau in their concentration is observed, where no further removal seems possible. This theory is proven by spiking a reactive sugar into the base and forming the mass balance over the system. Hence, in order to achieve a high reduction on high boiling wort flavours, another technology, such as adsorption, is required. To test, whether a suitable adsorbent can be identified, a wide screening experiment covering three adsorbent types (amine-functionalized polymers, hydrophobic resins and zeolites) and a total of 21 materials is performed. ZSM-5 type zeolites prove to have a superior selectivity as well as a relatively high capacity compared to other adsorbents. The choice of the right pore size and hydrophobicity is crucial for the separation success. Adsorption of the compounds of interest is non-competitive within the design space and robust against small changes in the beer matrix. The process is transferred to pilot scale, where it is shown that the zeolite effectively reduces wort off-flavour while maintaining the original character of the beverage. The reduced wort flavour concentration is also maintained over a period of 4 months ageing. Interestingly, the formation rates of aldehydes related to ageing are similar for the treated and reference product, with the exception of trans-2-nonenal, which is manifold lower in the treated AFB. A trained sensory panel confirms the difference in taste for both, the fresh and the aged product. In order to upscale this process to industrial scale, also the dynamics of the adsorption process on granular, binderless ZSM-5 zeolite is studied. The homogenous surface diffusion model is employed to regress the intraparticle diffusivity. The so obtained parameters indicate strong intraparticle mass transfer limitations as well as an inverse correlation of the effective diffusion coefficient to the molecules’ hydrophobicity. To avoid this process bottleneck, material improvements such as smaller crystal size and smaller granules are recommended. Finally, all obtained parameters are translated into a unit operation design. With a simple packed-bed operation of crushed particles, the production costs can be as much as 40 % lower than thermal dealcoholisation unit. Nonetheless, several assumptions still need to be verified, such as the material regenerability as well as other non- process-related factors such as material stability and food safety. Concluding, the newly developed technology for selective wort flavour removal in AFB in combination with restricted fermentation represents a great alternative to conventionally produced AFB.
...
The growing group of health-conscious consumers drives the development and sales in the market of low- or non-alcoholic beverages. In particular, sales in alcohol-free beer (AFB) has drastically gained in recent years, giving the incentive to further advance alcohol-free products. This thesis comprises the development of a new technology to produce an alcohol-free beer with an improved flavour, that is, an AFB with a significantly lower concentration in Strecker aldehydes. Despite the fact that Strecker aldehydes are present at trace concentrations of a few micrograms per litre, these compounds are majorly associated with the characteristic wort offflavour in alcohol-free beer. In the first stage, the origin of wort flavours is elucidated, and furthermore, the impact of the changed production process in comparison to regular beer and its resulting changes in the product is discussed. The most significant pathways of origin are the Maillard reactions and Strecker degradation, however, many other formation pathways have been suggested. While alcohol-free beers produced through regular fermentation and subsequent dealcoholisation are generally low in wort off-flavour, biologically produced AFBs exhibit a rather strong wortiness. This is because yeast’s activity during the fermentation is restricted to prevent alcohol formation, having the side effect that other compounds such as aldehydes are not converted to neutral or characteristic beer flavours. As it is impossible to prevent the formation of wort flavour, selective removal is required to produce an alcohol-free beer with improved flavour profile (balance). Subsequently, technologies applied to remove aldehydes from aqueous streams are investigated. Mechanisms that can be exploited for such removal are various – from separation based on size or volatility (distillation, pervaporation or membrane filtration) through sorption or conversion – past research has nearly studied all removal techniques available for aldehydes. However, most of the available techniques are not selective enough for a complex matrix such as beer, or not suitable for the application in the food industry. Nonetheless, adsorption is identified as the most promising technique to facilitate selective aldehyde removal. As a benchmark system, a dealcoholisation plant (spinning cone column) is studied with special focus on wort flavour removal. While volatile aldehydes such as 3-methylbutanal can relatively easily be reduced, methional, having a high boiling point, is not sufficiently separated from the end-product. Furthermore, due to the impact of heat, and ergo, the continuous formation and evaporation of these flavours, a plateau in their concentration is observed, where no further removal seems possible. This theory is proven by spiking a reactive sugar into the base and forming the mass balance over the system. Hence, in order to achieve a high reduction on high boiling wort flavours, another technology, such as adsorption, is required. To test, whether a suitable adsorbent can be identified, a wide screening experiment covering three adsorbent types (amine-functionalized polymers, hydrophobic resins and zeolites) and a total of 21 materials is performed. ZSM-5 type zeolites prove to have a superior selectivity as well as a relatively high capacity compared to other adsorbents. The choice of the right pore size and hydrophobicity is crucial for the separation success. Adsorption of the compounds of interest is non-competitive within the design space and robust against small changes in the beer matrix. The process is transferred to pilot scale, where it is shown that the zeolite effectively reduces wort off-flavour while maintaining the original character of the beverage. The reduced wort flavour concentration is also maintained over a period of 4 months ageing. Interestingly, the formation rates of aldehydes related to ageing are similar for the treated and reference product, with the exception of trans-2-nonenal, which is manifold lower in the treated AFB. A trained sensory panel confirms the difference in taste for both, the fresh and the aged product. In order to upscale this process to industrial scale, also the dynamics of the adsorption process on granular, binderless ZSM-5 zeolite is studied. The homogenous surface diffusion model is employed to regress the intraparticle diffusivity. The so obtained parameters indicate strong intraparticle mass transfer limitations as well as an inverse correlation of the effective diffusion coefficient to the molecules’ hydrophobicity. To avoid this process bottleneck, material improvements such as smaller crystal size and smaller granules are recommended. Finally, all obtained parameters are translated into a unit operation design. With a simple packed-bed operation of crushed particles, the production costs can be as much as 40 % lower than thermal dealcoholisation unit. Nonetheless, several assumptions still need to be verified, such as the material regenerability as well as other non- process-related factors such as material stability and food safety. Concluding, the newly developed technology for selective wort flavour removal in AFB in combination with restricted fermentation represents a great alternative to conventionally produced AFB.
BACKGROUND: Recently, a new process concept has been proposed to selectively adsorb wort off-flavours, i.e. aldehydes, from alcohol-free beers with hydrophobic zeolites. RESULTS: In this work, we investigated the uptake of a mixture of wort flavour compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, furfural, and methional), from a model solution onto binderless hydrophobic ZSM-5 zeolite granules in order to quantify mass transfer parameters and identify bottlenecks. Subsequently, the homogenous solid diffusion model was employed to regress the effective diffusion coefficients for each molecule and experimental condition, which ranged between 10−15 and 10−13 m2 s−1, indicating strong intraparticle mass transfer limitation. Furthermore, it was found that the effective diffusion coefficient is inversely correlated to the molecules' hydrophobicity, expressed as the logD value and its isotherm affinity constant. CONCLUSION: These results give valuable insight to design and improve the adsorbent material and an off-flavour removal unit at industrial scale.
...
BACKGROUND: Recently, a new process concept has been proposed to selectively adsorb wort off-flavours, i.e. aldehydes, from alcohol-free beers with hydrophobic zeolites. RESULTS: In this work, we investigated the uptake of a mixture of wort flavour compounds (2-methylpropanal, 2-methylbutanal, 3-methylbutanal, furfural, and methional), from a model solution onto binderless hydrophobic ZSM-5 zeolite granules in order to quantify mass transfer parameters and identify bottlenecks. Subsequently, the homogenous solid diffusion model was employed to regress the effective diffusion coefficients for each molecule and experimental condition, which ranged between 10−15 and 10−13 m2 s−1, indicating strong intraparticle mass transfer limitation. Furthermore, it was found that the effective diffusion coefficient is inversely correlated to the molecules' hydrophobicity, expressed as the logD value and its isotherm affinity constant. CONCLUSION: These results give valuable insight to design and improve the adsorbent material and an off-flavour removal unit at industrial scale.
The increasing popularity of alcohol-free beers (AFBs) fosters the industry interest in delivering the best possible product. Yet, a remaining sensory defect of AFBs is the over-perception of wort flavour, caused by elevated concentrations of small volatile flavour compounds (i.e. aldehydes). Previously, molecular sieves (hydrophobic ZSM-5 type zeolites) were found most suitable to remove these flavours by adsorption with high selectivity from the AFBs. In this work, a flavour-improved beer is produced at pilot-scale using this novel technology, and its chemical composition, sensory profile and stability are evaluated against a reference. Aldehyde concentrations in the flavour-improved product were found 79–93% lower than in the reference. The distinct difference was confirmed with a trained sensory panel and could be conserved even after three months ageing at 30 °C. Future work will focus on the process design to scale up this technology.
...
The increasing popularity of alcohol-free beers (AFBs) fosters the industry interest in delivering the best possible product. Yet, a remaining sensory defect of AFBs is the over-perception of wort flavour, caused by elevated concentrations of small volatile flavour compounds (i.e. aldehydes). Previously, molecular sieves (hydrophobic ZSM-5 type zeolites) were found most suitable to remove these flavours by adsorption with high selectivity from the AFBs. In this work, a flavour-improved beer is produced at pilot-scale using this novel technology, and its chemical composition, sensory profile and stability are evaluated against a reference. Aldehyde concentrations in the flavour-improved product were found 79–93% lower than in the reference. The distinct difference was confirmed with a trained sensory panel and could be conserved even after three months ageing at 30 °C. Future work will focus on the process design to scale up this technology.
A common sensory deficiency of alcohol-free beers (AFB) is caused by the presence of worty aldehydes. The aim of this study was to develop and proof the concept of a selective adsorption step, facilitating the removal of aldehydes from AFB. Therefore, the performance of 21 adsorbents (amine-functionalized polymers, hydrophobic resins and zeolites) was tested in wort. Among the studied adsorbents, hydrophobic ZSM-5 type zeolites (CBV28014, HiSiv3000 and ZSM-5 P-360) showed the best selectivity due to their 2-dimensional separation characteristics. Consequently, the obtained multicomponent isotherms in unhopped AFB revealed a linear adsorption behavior for all aldehydes, indicating non-competitive adsorption within the design space. The logarithms of the adsorption affinity constants were found to be linearly correlated to the compounds’ hydrophobicity and solubility. The concept was proven at pilot scale of 150 L, resulting in a reduction of aldehydes between 43.7–70.2 %, while conserving bitterness, pH and color of the AFB. Future work will focus on the sensory evaluation of the flavor-improved product.
...
A common sensory deficiency of alcohol-free beers (AFB) is caused by the presence of worty aldehydes. The aim of this study was to develop and proof the concept of a selective adsorption step, facilitating the removal of aldehydes from AFB. Therefore, the performance of 21 adsorbents (amine-functionalized polymers, hydrophobic resins and zeolites) was tested in wort. Among the studied adsorbents, hydrophobic ZSM-5 type zeolites (CBV28014, HiSiv3000 and ZSM-5 P-360) showed the best selectivity due to their 2-dimensional separation characteristics. Consequently, the obtained multicomponent isotherms in unhopped AFB revealed a linear adsorption behavior for all aldehydes, indicating non-competitive adsorption within the design space. The logarithms of the adsorption affinity constants were found to be linearly correlated to the compounds’ hydrophobicity and solubility. The concept was proven at pilot scale of 150 L, resulting in a reduction of aldehydes between 43.7–70.2 %, while conserving bitterness, pH and color of the AFB. Future work will focus on the sensory evaluation of the flavor-improved product.
Although present in concentrations in microgrammes per litre level, aldehydes, in particular those derived from Strecker degradation, are known to majorly contribute to the undesired wort flavour of alcohol-free beers. In order to improve currently available products, one needs to understand the underlying cause for the over-prevalence and identify leverage points and methods to selectively reduce the aldehydes in alcohol-free beers. This work gives a short overview on relevant flavour-active wort flavours identified in alcohol-free beer and on their involved chemical formation pathways. Consequently, aldehyde removal technologies in general and in brewing industry are presented. Adsorptive removal of off-flavours by aldehyde-scavenging groups is already widely exploited in the packaging industry and may achieve reduction of these components to near depletion, depending on the process conditions. Its principles are adaptable to recovering off-flavours before filling. Also, supercritical CO2 extraction has been successfully applied to separate flavours from food matrices. In brewing, the focus has been set to biologic conversion by restricted fermentation steps, but the reduction of key components of more than 70% is not achieved. Newer developments focus on thermal separation techniques that not only include non-specific physical dealcoholisation but also more selective technologies such as pervaporation, where aldehydes are reduced to near depletion. However, for most unit operations, selectivity and capacity are not yet investigated. Future research should explore the shortcomings of current techniques and overcome bottlenecks either by developing more specific methods for aldehyde removal and/or a clever combination of unit operations to optimise the separation and process integration.
...
Although present in concentrations in microgrammes per litre level, aldehydes, in particular those derived from Strecker degradation, are known to majorly contribute to the undesired wort flavour of alcohol-free beers. In order to improve currently available products, one needs to understand the underlying cause for the over-prevalence and identify leverage points and methods to selectively reduce the aldehydes in alcohol-free beers. This work gives a short overview on relevant flavour-active wort flavours identified in alcohol-free beer and on their involved chemical formation pathways. Consequently, aldehyde removal technologies in general and in brewing industry are presented. Adsorptive removal of off-flavours by aldehyde-scavenging groups is already widely exploited in the packaging industry and may achieve reduction of these components to near depletion, depending on the process conditions. Its principles are adaptable to recovering off-flavours before filling. Also, supercritical CO2 extraction has been successfully applied to separate flavours from food matrices. In brewing, the focus has been set to biologic conversion by restricted fermentation steps, but the reduction of key components of more than 70% is not achieved. Newer developments focus on thermal separation techniques that not only include non-specific physical dealcoholisation but also more selective technologies such as pervaporation, where aldehydes are reduced to near depletion. However, for most unit operations, selectivity and capacity are not yet investigated. Future research should explore the shortcomings of current techniques and overcome bottlenecks either by developing more specific methods for aldehyde removal and/or a clever combination of unit operations to optimise the separation and process integration.
