Y. ZHOU (1), Z. Lin (1), Y. Wang (1), H. Sun (1), S. Chen (1);
(1) Technical Centre, Beijing Yanjing Brewery Group Co. Ltd., Beijing, China
Technical Session 5 - Foam
Monday, June 15
10:45 a.m.–12:00 p.m.
Flores 1–2
In this study, protein analyzer and high performance gel filtration chromatography (HPGFC) were applied for qualitative and quantitative analysis of protein components in beer to investigate the influence of protein components on colloidal stability and foam stability and identify haze-active and foam-positive components. Comparing the changes in protein distribution and content in beer samples after a forcing test, total nitrogen in beer decreased and the content of protein under 25 kDa molecular weight (MW) was obviously reduced, while the proteins with an apparent MW >45 kDa were increased. The results demonstrated that proteins with an MW <25 kDa in beer were prone to oxidation and polymerization or interaction with other substances, forming macromolecular substances or insoluble haze particles in beer. Stepwise regression analysis showed proteins with an MW of 9.5 kDa and 0.9 kDa had a positive correlation with a sensitive protein. The higher the content of protein at 9.5 kDa in beer, the higher the EBC turbidity value. It suggested that when the 9.5 kDa protein exceeds 90 mg/L the shelf life of a beer would be affected. The content of protein components with an MW >5 kDa decreased significantly at around 30% in the foam-removed sample compared with the original beer. It revealed that beer foam contains high levels of proteins with an MW >5 kDa. It was worth noticing that the lower the content of MW 5–25 kDa proteins, the worse the beer foam performance. Therefore, beer foam-positive proteins mainly were distributed in the range of 5–25 kDa. The correlation of protein components and other physical-chemical parameters with beer head retention was analyzed. It indicated that the 43 kDa and 9.5 kDa proteins had a positive correlation with foam retention, while pH in the range of 4.0–4.6 had a negative influence. CO2 content had a significantly positive effect, while the impact of total polyphenols was not obvious. More beer samples (100) were determined for investigating the influence of protein components and iso-α-acid on foam retention using partial least squares regression (PLSR). Results suggested that protein components with an MW of 43 kDa, 9.5 kDa, and 2 kDa and iso-α-acid had more impact on foam retention, of which the 9.5 kDa protein was an important foam-positive protein and the advised level is 80–90 mg/L. Further study on protein components in wort after boiling was also carried out. Protein contents in Congress wort prepared by eight varieties of malts and in the wort after boiling for 30 min were measured. The results illustrated the >45 kDa proteins in wort decreased significantly after boiling. Metcalfe, Baudin, and Gan Pi #4 had relatively higher foam-positive protein contents in Congress wort, while Gan Pi #4, Metcalfe, and Scarlett had relatively higher foam-positive protein content in boiled wort. It is interesting that Metcalfe showed the least protein content variation after boiling, while Gairdner presented the largest variation.
Zhou Yunyun was born in 1987. She graduated with a master’s degree in bioengineering from Jiangnan University in 2013. Since 2013 she has been employed in the Technical Centre, Beijing Yanjing Brewery Group Co. Ltd., Beijing, China.
