Understanding the colloidal and aromatic stability of dry-hopped beer

Abstract

This thesis documents investigations of flavour stability and sporadic haze formation. Historical data was collected to statistically assess process derivations impacting sporadic increases in turbidity. Spearman’s rank-order correlation coefficients did not find significant relationships between brewing, conditioning, and filtration/packaging on the increase of turbidity. Therefore, diagnostic studies were used to gradually eliminate potential sources of observed sporadic spikes in turbidity. Concentrations of high molecular weight β-glucans, total protein, and polyphenol were measured in low (≤ 5.0 EBC), high (≥ 5.0 EBC), and control (different brand, always ≤3.0 EBC) samples. Additionally, beer samples were digested with Ultraflo®Max, amyloglucosidase, and pepsin to digest β-glucans, residual starches/dextrins, and protein, respectively. The enzymatic digestion studies saw the greatest differences pre and post digestion by the addition of pepsin. The wet-chemical tests revealed that only β-glucan contents were elevated in high haze samples. Results indicated that mannoproteins were a culprit of turbidity. The use of LC-QTOF-MS and an assay for D-mannose, D-fructose, and D-glucose confirmed this supposition. Flavour-stability studies examined the solubility and extraction rate of hop terpenes into beer, the use of sensory analysis to trace the change in flavour/aroma over time, and an assay-development for the quantification of terpene concentrations in beer. As each hop variety contained different essential oil compositions, a linear extraction rate could not be determined. In addition to this, the chemistry of each hop terpene/terpenoid differs in chemical composition and are more/less soluble in different concentrations of ethanol. Overall, sensory and analytical data analyses did not find any strong relationships. However, the presence of β-myrcene could be linked to fresh beer less than 14 days old. Finally, the Vanillin assay was adapted to develop an assay to determine the concentration of terpenes/terpenoids in beer. Unfortunately, terpene concentrations in beer are too low to be detectable in the assay and the isolation/concentration methods were not successful. However, there is future potential to develop the assay by utilising methanol in place of ethanol and assessing one class of terpenes, such as monoterpene oxides, instead of multiple classes of terpenes. The combined results of this work provide more information to brewers, packaging technologists, and quality laboratories on how raw materials impact the quality of the final product, and therefore increasing the likelihood of consumers experiencing high quality, flavour stable products.