Influence of the time of bilberry (Vaccinium myrtillus L.) addition on the phenolic and protein profile of beer.

Background: In recent years, there has been an increased fruit addition to the brewing process, especially in craft breweries. Fruit addition leads to changes in the organoleptic characteristics and chemical composition of beers. Bilberries are rich in phenolic compounds and possess significant antioxidant capacity. The effects of bilberry addition and brewing process parameters on the changes in the phenolic and protein profile of beer have not been sufficiently studied. The aim of this research was to investigate the changes in the individual phenolic compounds and the protein fractions in beer when bilberries were added at different maturation stages.

Methods: An infusion mashing method was applied for the purpose of obtaining wort with an original extract of 14°P after boiling. Pilsner malt, bitter and aromatic hops 60/40 (Perle and Cascade, respectively), dry yeast Saccharomyces pastorianus (carlsbergensis) Saflager W 34/70, and bilberries (Vaccinium myrtillus L.) were used. All processes were conducted in a Home Brew 50 all-in-one 50 dm3 brewing system. The fermentation was carried out in a stainless steel cylindroconical fermenter at a temperature of 14°C. The “green beer” was transferred to small stainless-steel fermenters after 60% of the original wort extract had been fermented. The maturation continued for 14 days at 14°C, and the beer lagering for 5 days at 2°C. The bilberries were pasteurised in a water bath for 10 minutes at 70°C. After cooling, they were added to small fermenters at a concentration of 167 g/dm3 at the beginning and on the seventh day of beer maturation. All variants were carried out in duplicate. After lagering, the beer was bottled using a “beer gun”. The beer samples from the experiments were filtered on the day of bottling and frozen until analysis. HPLC/UV-VIS and electrophoresis were used to determine the phenolics and proteins, respectively. The total monomeric anthocyanins were determined by the pH differential method. The original wort extract and alcohol concentration were evaluated, and the sensory analysis was performed according to EBC standard methods.

Results: The changes in 10 phenolic acids, 7 flavonoids, and 10 protein fractions in beer with bilberries added at the beginning and on the seventh day of maturation were studied. The addition of bilberries led to an increase in the phenolic acid (3-fold) and flavonoid (6.2-fold) concentrations. The highest enrichment was observed in terms of rutin, chlorogenic, caffeic, and 3,4-dihydrobenzoic acids. Rosmarinic acid and monomeric anthocyanins were only detected in the bilberry beers. Chlorogenic and neochlorogenic acids, rutin, and catechin dominated in the bilberry beers. Neochlorogenic and gallic acids, epicatechin, and catechin dominated in the bilberry-free beers. The addition of bilberries reduced the protein content by 93 to 96%. The number of protein fractions decreased from 10 to 4. The influence of the bilberry addition time on the phenolics and proteins was different, and it affected the individual protein fractions in a different way. More phenolic acids and flavonoids were determined when bilberries were added at the beginning of maturation. The losses of some protein fractions were higher at the beginning of maturation and of others on the seventh day of maturation, whereas the addition time did not matter for some of the fractions.

Conclusions: This study provides new information related to the changes in the phenolic and protein profile of beer with bilberries depending on the time of bilberry addition during beer maturation. The protein concentration and number of protein fractions decreased dramatically. In spite of the significant protein losses, the bilberry addition improved the phenolic profile of the beer and its organoleptic characteristics. The presence of more phenolic compounds is related to the antioxidant capacity respective to the biological value of beer. Further research in this direction is needed.