Optimization of microbrewing process for high quality gluten free beers production

Beer is one of the most ancient and consumed beverages worldwide. It is traditionally produced from water, barley, hop and yeast. However, barley contains gluten, the protein fraction from wheat, rye, barley, spelt, kamut, oats or their crossbred varieties, to which some persons are intolerant, as defined by Codex Alimentarius. For this reason, beer is not considered safe for coeliac people. In fact, the only therapy against the coeliac disease is to follow a strict gluten free (GF) diet, avoiding foods and beverages containing gluten. Although during all brewing process there is a natural gluten reduction, most of beers still contain a gluten content above the GF safe threshold (20 ppm) established by Codex Alimentarius. Therefore, different strategies for GF beers production have been developed in the last years, in order to satisfy the requirements of people with nutritional issues. The main approaches to produce GF beers are the use of GF cereals and pseudocereals and the application of gluten reduction treatments. Among these latter, the use of prolyl endopeptidase from Aspergillus niger (AN-PEP) is the most common and easiest solution to produce GF beer without excessively altering the conventional brewing process. However, there are conflicting opinions about the safety of the enzymatic-treated beers due to the possible presence of underestimated immunopathogenic peptides remaining in the final beer. Therefore, the replacement of barley malt with GF cereals or pseudocereals is a safer alternative to produce GF beer, even if the use of GF grains in brewing may alter the brewing parameters and sensory profile of the final beer. The aim of this Industrial PhD project is the development and optimization of a GF beer by replacing 40% of barley malt with GF grains, taking into account both technological and sensory aspects. This project was funded by the Basilicata Region (Italy) and it saw the involvement of “Birrificio 79 srl” in Matera (Italy) as Industrial partner, “Italian Brewing Research Centre (CERB)” with which the School of Agriculture, Forest, Food and Environmental Sciences (SAFE) has concluded a framework agreement for scientific and technical cooperation, and Ghent Technology Campus (Belgium) as Host Institution partner. PhD activities were carried out in a scale-up approach, from laboratory to micro-industrial scale, and they are described as follow: 1. Assessment of brewing attitudes of GF grains (sorghum, millet, buckwheat, quinoa and amaranth) on laboratory scale; 2. Laboratory scale optimization of grist composition and mashing conditions in order to develop the best performing beer with proper brewing parameters and the highest consumers acceptability; 3. Validation of the optimized formulation on pilot-scale at Ghent Technology Campus, with the aim to implement technological advances and to better control all of the brewing step that could promote a natural gluten reduction; 4. Development of a GF craft beer on micro-industrial scale at Birrificio 79 srl, industrial partner of this PhD project, brewed with unconventional GF grains, without the need to use processing aids. The first activity of the PhD project focused on the study of the scientific literature concerning the GF beer production: first of all, topics related to gluten-related disorders, official method for the determination of gluten in foods and beverages, legislation and market of GF products were detailed; then, a comprehensive overview of all GF brewing practices was provided, focusing on strengths and weaknesses of each of them, taking into account both physicochemical and sensory attributes (Chapter 1). The analysis of the literature showed that the use of non-gluten-containing grains in brewing could be a suitable approach in producing GF beer but still needed more-in-depth tools to optimize the brewing process. “American Pale Ale” beer style from the brewery “Birrificio 79 srl” (Matera, Italy), industrial partner of this PhD project, was chosen as control sample (all-barley malt beer) since it was the one with the lowest gluten content (39±8 ppm). For the laboratory scale (10L, University of Basilicata, Italy) activities, five unmalted GF grains were selected: sorghum, millet, buckwheat, quinoa and amaranth. The selection of the GF grains used was made according literature review and in order to meet the requirement of the Industrial partner of this PhD: in particular, amaranth was selected because there is a research gap since there are very few studies in literature concerning its use in brewing, and sorghum was selected because it was of interest for the microbrewery “Birrificio 79 srl”. They were used as adjuncts (barley malt substitutes) in the maximum concentration of 40%, which corresponds to the maximum concentration of barley malt that can be replaced, according to the Italian legal definition of beer. Each GF grain was used in brewing both with and without a pre-gelatinization step to evaluate the impact of gelatinization step on brewing attitudes of unmalted GF grains (Chapter 2). On the basis of the results of physicochemical and sensory analyses performed on final beers, sorghum and quinoa were selected for the subsequent activity. Central Composite Design (CCD) was performed to optimize the grist composition and mashing conditions to formulate a GF beer with proper brewing parameters and the highest sensory score in terms of consumers acceptability. Grist composition (X1), expressed as sorghum:quinoa ratio, was chosen as independent variable in order to individuate the proper combination between sorghum and quinoa that does not adversely affect both brewing parameters and hedonic ratings of final beer. In addition, it was hypothesized that a longer protein rest may enhance the protein breakdown, also influencing the gluten content. For this reason, time of protein rest was selected as independent variable (X2) (Chapter 3). The optimized formulation was subsequently validated on pilot-scale (5hL, Ghent Technology Campus, Belgium). At the same time, a comprehensive comparison among the main GF brewing approaches was carried out, with a focus on their gluten reduction ability and their impact on standard quality attributes and sensory acceptance. Moreover, the influence of a longer cold maturation on a natural reduction of gluten content was investigated in order to find out whether a gluten reduction is possible without the application of processing aids (Chapter 4). Then, the experimental design was transferred on micro-industrial scale (6hL, Birrificio 79 srl, Matera). The beer brewed with sorghum and quinoa and the enzymatic-treated sample were produced and characterized from physicochemical and sensory point of view. In addition, the influence of brewing process and raw materials information on consumers acceptability, willingness to buy, willingness to pay and consumers sensory perceptions was investigated (Chapter 5). Based on the results of this PhD project, it can be concluded that it is possible to produce a marketable GF craft beer simply by partially replacing barley malt with 6% of sorghum and 34% of quinoa and by taking practical measures in order to produce a wort with an original low gluten content, for example dilution of pre-boil wort as much as possible, vigorous boiling step, efficient lautering and whirlpool step. Therefore, reaching a gluten concentration below the GF threshold, even without the need to use enzymes generally used for gluten reduction purpose, allows to avoid the possible drawbacks of the enzymatic treatments. Therefore, this study provides promising results for the GF craft brewing sector creating greater differentiation in the market.