Unfilterable Beer Haze Part II: Identifying Suspect Cell Wall Proteins

Abstract

The use of various diagnostic techniques has been previously utilized in the assessment of a commercially available India Pale Ale with cases of sporadically occurring unfilterable haze. The results from Part 1 suggested that β-glucans and proteins were the cause of the unfilterable haze and it was postulated that cell wall mannoproteins may also be a culprit of the unfilterable beer haze. In this follow-up study, proteins from high haze and low haze beer samples were precipitated and assessed using SDS-PAGE. Polyphenol interferences observed on the SDS-PAGE indicated that protein purification and targeted analysis was required. Proteins from high haze and low haze samples were fractionated and qualitatively identified via LC-MS. A library was built from FASTA sequences of targeted yeast proteins to qualitatively analyze the high haze and low haze samples. The protein fractionation was successful at purifying and isolating proteins from high and low haze samples. Two protein peaks were observed in the high haze sample, while one protein peak was observed in the low haze sample. The targeted LC/MS analysis discovered the presence of yeast cell wall mannoproteins and flocculation proteins, particularly Flo1 and Flo9. Understanding the source of these hazes can provide an opportunity for brewers to mitigate against their formation by adjusting brewing and yeast management practices.

The Influence of Biomolecule Composition on Colloidal Beer Structure

“…Polyphenols, sugars and reducing substances, bitter resins, etc., accompanying protein substances play the role of accompanying compounds in the formation of a colloidal structure, supporting the spatial structure of protein molecules, the so-called “buffering capacity” both with respect to foam proteins and other protein structures [ 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 ].…”

“…The content of mannose polymers, expressed as mannan, for beer was at the level of 120–180 mg/L and is a consequence of the use of grain raw materials and microorganisms in the process [ 80 ]. Mannans in the structure of beer can be linked with proteins and represent compounds of yeast cells—mannoproteins involved in the haze formation [ 81 ].…”

Effects of Dry-Hopping on Beer Chemistry and Sensory Properties—A Review

“…Huismann et al [ 139 , 140 ] found in unfilterable dry-hopped India Pale Ale, that the haze was caused by β-glucans and proteins. The authors suggested that this type of haze was due to the presence of unfilterable yeast cell wall mannoproteins in the beer.…”

Proteomics and glycoproteomics of beer and wine

“…A proteomics based study of commercial India Pale Ale diagnosed that overall protein and β‐glucan content were associated with this haze, and postulated that cell wall mannoproteins secreted by yeast were the primary cause [56]. A follow‐up study used protein fractionation, SDS‐PAGE and LC‐MS to reveal that both yeast cell wall mannoproteins and flocculins Flo1 and Flo9 were the most abundant proteins associated with unfilterable haze, providing avenues for future research to avoid problematic haze formation [57].…”