The colloidal stability of craft beers obtained with gluten-free adjuncts: an assessment of aspects related to technology, composition and analysis

This project aims to study issues related to the physical and chemical stability of craft beers. Specifically, the plan is to analyze how some variables in the malting process (i.e., pH of the first steeping water) and formulation (use of gluten-free adjuncts) can contribute to the colloidal stability (shelf-life) of the final beer. The primary aim of the study was to carry out micro malting tests in the laboratory on four gluten-free cereals/pseudocereals (millet, amaranth, buckwheat and quinoa) in order to identify the optimal conditions for obtaining malts suitable for the production of craft beers. The use of an alkaline solution in the first steeping may facilitate the extraction of proteinaceous and phenolic fractions from seeds; for this reason the pH of the first steeping water was modified. Quality of malts was checked analysing diastatic power, beta glucans content and Kolbach index (soluble nitrogen content as a percentage of total nitrogen). Nine beers with different formulations were produced in the laboratory (2 L, micro-brewing): beer made with 100% barley malt (reference sample), beers with 40% substitute gluten-free malt using the best malts obtained from the micromalting tests and 60% of barley malt. The use of gluten-free substitutes was intended to reduce the base level of the protein fractions rich in proline. The evaluation of beer stability was carried out analyzing some indices validated by EBC (European Brewery Convention) (sensitive proteins and cold turbidity respectively), and two unconventional methods (gluten analysis and antioxidant activity, AA) to verify the possible correlation among these analyses and the official methods. Measurements of beer AA, which is mainly due to the polyphenol content, could give useful information on the colloidal stability of the final beer product. Subsequently, the experimental plan was transferred on a larger scale; three beers were produced at the pilot plant of University of Udine (capacity of 200 L) using only the malt with the highest diastatic power (buckwheat): the first with 100% malted barley (reference sample), the other two with increasing amounts of malted buckwheat (20 and 40%). The colloidal stability of beer samples was tested with the same four analyses used to verify physico-chemical stability of the laboratory produced samples. The results obtained from the micromalting tests were in line with the expectations: the four gluten-free cereal/pseudocereals were under-modified if compared to traditional malts, but potentially suitable as adjuncts (especially buckwheat). The unconventional methods used to study the physico-chemical stability of craft beers provided encouraging results: either gluten analysis or the crocin test (AA) data showed trends correlated with those obtained with the validated method (alcohol chill haze). Specifically, the gluten analysis discriminated the beers produced at the pilot plant better than sensitive proteins (EBC method). Based on the collected results, it can be concluded that the use of gluten-free adjuncts, combined with relevant process conditions (i.e. alkalinized first steeping water in the malting process), could lead to more stable final products with a gluten content less than 100 mg/L and so potentially suitable by coeliacs. The colloidal stability monitoring of the beers produced at the pilot plant has already been planned, as well as the descriptive sensory analysis of the same samples.