Beer aroma

The beers in Table 11, with the exception of lunch beer, have an original gravity of 6.4—8.1°P. The alcohol content is 0.65—3.4% vol the remaining extract is 3.9—7.1°P. Since the aroma of beers is obtained mainly during fermentation, beers having Htde or no alcohol produced with no or intermpted fermentation are lacking in "tme" beer aroma. Previously aroma was improved through addition of small amounts of yeast (2—10 mg/L) to the unfermented beer. The addition usually takes place just prior to filtration. 

The enantioconvergent biohydrolysis of sterically demanding trisubstituted oxiranes has also been reported [189,190]. For instance, the enantioconvergent hydrolysis of a trisubstituted rac-epoxide (Figure 6.70) was a key step in the chemoenzymatic synthesis of a volatile constituent of the beer aroma [190]. 

Beer Aroma staling Increase of esters, methional and phenylacetaldehyde [116]... 

Komarek, D., Schieberle, P. (2003) Changes in key beer aroma compounds during natural beer aging. In CadwaUader, K.R., Weenen, H. (eds.) Freshness and Shelf Life of Foods. ACS Symposium Series 836, pp. 70-79... 

Low alcohol or alcohol-free beers of 0.5-1.3% alcohol may be produced by interruption of the fermentation, by boiling of the beer to distill part of the alcohol, by vacuum distillation, or by alcohol removal by reverse osmosis. The first two methods are the most common [16]. However, these methods result in the loss of desirable aroma substances along with the alcohol. This is remedied with used yeast, which is a reservoir of aroma substances. This is added at 2-10 mg/L to the dealcoholized beer just before filtration to restore the beer aroma. 

The most easily definable hop contribution to beer aroma is a floral flavor note that certain hop varieties (not necessarily the traditional "aroma hop" varieties) impart to beer ( ). Indications are (Table I) that the floral compounds linalool and ger-anlol are responsible for this aroma note. Geranyl isobutyrate, though present in the more floral beers, is probably in too low concentration to have a major effect on beer flavor. a-Terplneol is eliminated from consideration for the same reason. Linalool has been reported in beer at an estimated concentration of 34ppb ( 3) by Lindsay and at a concentration of 470ppb ( 7) by Tressl. 

Some classical examples of application are the separation of azeotropique mixture [71], the isomeric mixture separation, the dehydration of organic mixtures, and fruit juice concentration, alcohol extraction from wines and beers, aroma extraction [72], etc. 

This was applied to the synthesis of beetle aggregation pheromones exo- and ewiio-brevicomin, exo-isobrevicomin and (-)-frontalin (Fig. 1.8). A volatile contributor of beer aroma was also synthesised [25, 26]. The synthesis of these natural products also showed the ability of ZrCU to successfully deprotect 1,3-dioxolane groups. 

Besides the yeast conversion of phenolic adds into flavour-active volatile phenols that may have an adverse impact on beer aroma as discussed above, there is an interest in the contribution of phenolic acids to beer antioxidant activity (Piazzon et al 2010). Indeed, the use of hydrolytic enzymes (e.g. esterases) to release phenolic adds during mashing has been reported (Szwajgier, 2011). It must be cautioned that boosting the level of phenohc acids snch as fendic acid in the wort may inaease the content of volatile phenols in the finished product, and a flavour defect may ensue. 

Saison, D., De Schutter, D. R, Vanbeneden, N., Daenen, L., Delvaux, R, Delvaux, F. R. (2010). Decrease of aged beer aroma by the reducing activity of reducing yeast. Journal of Agricultural and Food Chemistry, 58, 3107-3115. http //dx.doi.org/10.1021/ jf9037387. 

Thiazole and its derivatives are detected in foods such as coffee, boiled meat, boiled potatoes, heated milk and beer. Aroma extract dilution analyses show that among the compounds I-in in Table 5.22, 2-acetyl-2-thiazoline (II) contributes most intensively to the aroma of quick fried beef. Model experiments showed that cysteamine, formed by the decarboxylation of cysteine, and 2-oxopropanal are the precursors. It was also found that higher yields of II are obtained at pH 7.0 compared to pH 5.0. The intermediates in the reaction path to thiazoline II (Fig. 5.21) were identified as the odorless 2-(l-hydroxyethyl)-4,5-dihydrothiazole (a) and 2-acetylthiazolidine b), which are in tautomeric equilibrium, presumably with 2-(l-hydroxyethylene)thiazolidine (c) as the intermediate compound (Fig. 5.21). The intermediates a and b are oxidized to thiazoline II by atmospheric oxygen in the presence of catalytic amounts of heavy metals. It is assumed that the... 

Enantioconvergent biohydrolytic access to a volatile contributor of beer aroma. 

Steinreiber, A., Mayer, S.E and Faber, K. (2001) Asymmetric total synthesis of a beer-aroma constituent based on enantioconvergent biocatalytic hydrolysis of trisubstituted epoxides. Synthesis, 13, 2035-2039. 

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