The influence of metal ions on concentrations of flavour-active sulphur compounds measured in beer using dynamic headspace sampling

Addition of copper(II) ions (≤1.6 mg litre^?1) to beer significantly reduced (P ≤ 0.05) concentrations of hydrogen sulphide and ethanethiol measured in beer, but had no effect on methyl sulphide, methyl thioacetate and methyl disulphide. Zinc, iron(III), manganese(II), nickel, lead(II) and tin(II) ions, at similar concentrations, had no effect on any of the sulphur volatiles. When metal ions were added at a concentration of 1 glitre^?1 zinc, iron(III) and lead(II) reversibly bound hydrogen sulphide and enthanethiol.     

THE INFLUENCE OF ENTEROBACTER AGGLOMERANS ON BEER FLAVOUR

The influence of Enterobacter agglomerans (Erwinia herbicola) on the fermentation process and beer flavour was studied. The presence of E. agglomerans gave rise to increased levels of acetaldehyde, methyl acetate, diacetyl, 2,3-pentanedione and dimethyl sulphide in the final product. The concentration of these compounds was affected by the number of bacterial cells inoculated into the pitched wort.     

ESTIMATION OF VOLATILE SULPHUR COMPOUNDS IN BEER

A method has been developed for the quantitative estimation of volatile sulphur compounds in beer at levels below 0.1 μg litre^?1. The method relies on the concentration of beer headspace volatiles onto a porous polymer followed by injection into a capillary gas chromatographic column using a thermal desorption cold trap injector. The volatile components are separated using temperature programming and detected by a flame photometric detector specific for sulphur compounds. The mean concentrations and the estimates of r₉₅ (μg litre^?1) for volatile sulphur compounds measured in a commercial lager were respectively: methanethiol (0.33, 0.30); dimethyl sulphide (19.3, 5.3); carbon disulphide (0.42, 0.32); ethylene sulphide (0.37, 0.05); 1-propanethiol (0.11, 0.02); methyl thioacetate (11.7; 2.7); methyl disulphide (0.34, 0.42). The method is a significant improvement over previous techniques for the quantification of sulphur-containing volatiles in beer .     

THE PRODUCTION OF HYDROGEN SULPHIDE BY YEAST AND BY ZYMOMONAS ANAEROBIA

Radiochemical experiments indicated that most of the free hydrogen sulphide excreted by a brewing yeast in wort and by Zymomonas anaerobia in beer was derived from sulphate. Sulphate was also assimilated by the organisms but most of their cellular sulphur was derived from other sources. In a synthetic beer medium, excessive amounts of hydrogen sulphide were liberated by Z. anaerobia when pantothenate was deficient. Sulphate and zinc ions stimulated sulphide production by the bacterium.     

ON THE DETERMINATION OF VOLATILE THIOLS IN BEER

The method of Ikeya for the determination of volatile thiols in beer by aspiration of these compounds into mercuric acetate has been examined. Cadmium acetate has been found to be unsuitable as an absorbant for removing hydrogen sulphide since it also combines with thiols. This reagent has been replaced by aqueous zinc acetate in a separate absorption trap. The proposed modification has the advantage of enabling estimations of hydrogen sulphide and of volatile thiols to be carried out on the same sample.     

LIPID METABOLISM AND THE REGULATION OF VOLATILE ESTER SYNTHESIS IN SACCHAROMYCES CEREVISIAE

The specific rates at which ethyl acetate and iso-amyl acetate are produced by yeast increase markedly at that point in fermentation where syntheses of lipids (i.e. saturated fatty acids and squalene) stop. An increase in the acetyl-CoA: CoASH ratio, or a reduced availability of substrates (fatty acyl-CoAs) for acyl transferases, are possible reasons for such a stimulation of ester synthesis. Increased rates of ester production are not sustained but contribute significantly (ca. 30% for ethyl acetate) to the total concentration of acetate esters in beer fermented from 1·040 all-malt wort. Addition of linoleic acid (50 mg litre^?1) suppresses the induction of ester synthesis and reduces overall formation of both ethyl and iso-amyl acetates by ca. 80%. Possibly, linoleic acid exerts these effects either by directly inhibiting the activity of an ester-synthesising enzyme, or by allowing alternative use of acetyl-CoA for the synthesis of saturated fatty acids.     

THE INFLUENCE OF HAFNIA PROTEA (OBESUMBACTERIUM PROTEUS) ON BEER FLAVOUR

Numerous strains of Hafnia protea (originally Obesumbacterium proteus) were grown in brewer's wort in the absence and presence of Saccharomyces cerevisiae. The presence of H. protea gave rise to increased levels of n-propanol, isobutanol, isopentanol, dimethyl sulphide, dimethyl disulphide and 2,3-butanediol in finished beer. Concentrations of dimethyl sulphide and dimethyl disulphide varied according to the bacterial strains, but the increased levels of fusel alcohols and 2,3-butanediol were strain-independent.     

Pilot‐scale brewing using self‐cloning bottom‐fermenting yeast with high SSU1 expression

A pilot‐scale fermentation was performed using SSU1‐overexpressing bottom‐fermenting yeast strains constructed by ‘self‐cloning’. In these strains, the gene SSU1, encoding a plasma membrane protein that excretes sulphite, was highly expressed. The rate of fermentation of the two SSU1‐overexpressing strains tested showed some reduction during the mid‐fermentation phase as compared with the parental strain. These differences, however, did not affect overall fermentation and the final apparent extracts had decreased to a level normally obtained during brewing. The concentration of hydrogen sulphide in the wort remained low during fermentation in the case of the two self‐cloning strains compared with the parent. The concentration of 2‐mercapto‐3‐methyl‐1‐butanol, a sulphur compound that causes an ‘onion‐like’ off‐flavour, was also reduced in the case of the self‐cloning strains, a result confirmed by sensory evaluation of the beer immediately after bottling. Furthermore, with these strains the anti‐oxidation potential of bottled beer, as measured by electron spin resonance, was improved and the concentration of trans‐2‐nonenal in bottled beer after 7 days of accelerated aging at 37°C was decreased. These observations, together with the lower stale flavour score determined by sensory evaluation of bottled beer after a month of aging at 25°C, indicated that the flavour stability of the beer had been successfully improved. Copyright © 2013 The Institute of Brewing & Distilling     

Nuclear Magnetic Resonance Methodology for the Analysis of Regular and Non-Alcoholic Lager Beers

The presence of seven main agents responsible for beer aroma and taste (n-propanol, isobutanol, 3-methylbutanol, tyrosol/tyrosine, ethyl acetate, isoamyl acetate, and acetaldehyde) is determined by different nuclear magnetic resonance (NMR) techniques (¹H PRESAT, total correlation spectroscopy, heteronuclear single quantum correlation, and heteronuclear multiple bond correlation) in five regular and five low-alcoholic or alcohol-free beers. The new methodology includes the identification of the ¹H and ¹³C NMR chemical shifts of the analytes by a standard addition method and the consequent identification of the compounds studied in regular and non-alcoholic beers. The chemical composition is different depending on whether the beer is regular or non-alcoholic, therefore affecting the organoleptic characteristics of each type of beer.     

ZYMOMONAS AND ACETALDEHYDE LEVELS IN BEER

High acetaldehyde levels in beers during processing were found to be due to infection with Zymomonas anaerobia. Acetaldehyde only appeared in the absence of yeast and the level was correlated with the concentration of Z. anaerobia as determined by the time taken to produce hydrogen sulphide in a primed beer forcing test.     

Effect of Carbonyl Sulphide (COS), Ethyl Formate (EF) and Carbon Disulphide (CS2) on the Malting Quality of Barley and the Flavour Profile of Beer

New fumigants are needed to control grain insects because methyl bromide is being phased out as an ozone‐depleting substance under the Montreal Protocol and because resistance to phosphine is increasing. Alternative fumigants also provide one strategy to manage resistance. To assess the effect of candidate fumigants on barley quality, malting and brewing trials were conducted with malting barley (Schooner), 9.4% moisture content, fumigated with carbonyl sulphide (COS), ethyl formate (EF) and carbon disulphide (CS₂) at concentrations of 20, 90 and 36 mg/L respectively for 7 days at 20°C in riveted steel silos containing 33 t of barley. The appropriate industry body, the Malting and Brewing Industry Barley Technical Committee (MBIBTC) set the quality parameters to be evaluated and allocated work to the appropriate quality laboratories. Germination of fumigated barley was not affected by the fumigants. Residues of COS, EF and CS₂ in outloading barley samples were 0.085 ± 0.0052, 0.4 ± 0.1 and 2.22 ± 0.07 mg/kg respectively, which were below the experimental permits of maximum residue levels (MRL). Residues of COS, EF and CS₂ in malt, wort and beer were indistinguishable from those in unfumigated (or non‐fumigated) barley. Ethyl formate and CS₂ affected wort in increasing the apparent attenuation limit (AAL) and CS₂ affected barley colour. Sulphur volatiles in the trial beer made from EF and CS₂ (unlike COS) fumigated barley decreased significantly. Beer from COS, EF and CS₂ fumigated barley had a somewhat higher 24‐hour chill haze level (0.62–0.84) than beer from the untreated barley (0.53). The total alcohols and isoamyl acetate increased in beer made from EF fumigated barley. Carbonyl sulphide, EF and CS₂, however, had no effect on beer flavour or quality.     

Analysis of polysaccharide and proteinaceous macromolecules in beer using asymmetrical flow field‐flow fractionation

This paper demonstrates the potential of asymmetrical flow field flow fractionation coupled with online multi‐angle light scattering, differential refractive index and UV detection for the fractionation and analysis of macromolecules in beer regarding their composition, molar mass (M) and relative concentration. The macromolecules in the liquid and foam of two types of beer, light lager and porter, were analysed in their native state with minimal sample preparation. The results showed the presence of three major populations of macromolecules. In lager beer liquid, the early eluting population has an average M of 2 × 10⁴ g/mol and an intense UV absorbance at 280 nm suggesting the presence of proteinaceous macromolecules. The second and the third populations, which elute at consecutively longer retention times, have M ranging from 10⁵ to 10⁷ g/mol. They are not UV‐active at 280 nm, suggesting the elution of polysaccharides. The second population was identified as β‐glucans as a result of β‐glucanase treatment. The third population was not identified in the present study. The results show that similar populations are present in lager beer foam and that the macromolecules appear to be present in a more aggregated state. The M range of macromolecules in porter beer liquid ranged from 10⁵ to 10⁸ g/mol. A fraction of macromolecules eluting at longer retention times is highly UV‐active, which shows that there are great variations in the macromolecular profile of lager and porter beer. Copyright © 2015 The Institute of Brewing & Distilling     

The effects of herbal pre-seasoning on microbial and oxidative changes in irradiated beef steaks

This study was undertaken to examine the effects of electron beam (e⁻ beam) irradiation, with and without pre-seasoning with ginseng and garlic herbs, on microbial growth and oxidative stability of beef sirloin steaks. All dosages (e.g. 2, 3 and 4 kGy) of e⁻ beam irradiation were effective at reducing the population of psychrotrophic bacteria in beef steaks. A further reduction in psychrotroph count was observed with the pre-seasoning of garlic, in both non-irradiated and irradiated steaks. The use of 3 and 4 kGy irradiation dosages, however, increased lipid oxidation during 4 weeks of storage. Ginseng decreased malondialdehyde concentrations in sirloin steaks more than garlic after e⁻ beam irradiation of meats but had no effect on psychrotroph count. Inhibition of lipid oxidation by ginseng also minimized the discolouration of surface redness on sirloin steaks. The pre-application of garlic to irradiated steaks resulted in a lower hardness value and relative moisture loss. Electron beam irradiation, after pre-seasoning with ginseng or garlic, was shown to enhance the quality of beef sirloin steaks.     

NITRATE REDUCTION AND ATNC FORMATION BY BREWERY WILD YEASTS

Control of NAD(P)H-dependent nitrate reductase (NR) and nitrite reductase (NiR) synthesis and activity in Hansenula anomala, Rhodotorula glutinis, Candida versatilis and Brettanomyces anomalus was investigated. Activities of both enzymes were high in all four yeasts when cultured in a medium containing nitrate as the sole source of cell nitrogen, but ammonia and amino-nitrogen were shown to rapidly repress nitrate assimilation and reduction. Little or no NR or NiR activity was detected in wort or beer-grown cultures. Only B. anomalus was found to excrete nitrite when grown in wort, but not at a concentration which could be chemically reduced to allow formation of a detectable concentration of N-nitrosamines. Cask beer (containing 16 mgl^?1 nitrate) contaminated with nitrate reducing wild yeasts, pre-grown on nitrate, contained < 10 μgl^?1 Apparent Total N-Nitrosocompounds (ATNC) following 10 weeks storage. It was concluded that contamination of wort, fermentation and finished beer by nitrate-reducing wild yeast is unlikely to result in formation of detectable ATNC .     

Fermentation optimization for a probiotic local northeastern Indian rice beer and application to local cassava and plantain beer production

Response surface methodology was employed to determine the optimal conditions of time and temperature for the fermentation of a local North East Indian rice beer. The same conditions were then applied to prepare local beers from cassava (Manihot esculanta) and plantain (Musa ABB). Saccharomyces cerevisiae, Aspergillus oryzae and Lactobacillus plantarum were used to carry out the fermentation process. Thirteen experimental runs, based on a two‐factor five‐level design were carried out according to a central composite rotatable design. The independent variables were fermentation time (24–216 h) and temperature (25–40°C). The responses studied were content of protein, alcohol, total polyphenols, reducing sugars as well as titratable acidity and L. plantarum count. Numerical optimization predicted that a fermentation period of 143 h at a temperature of 33°C would result in a desirable rice beer, with response values of protein content OF 0.77%, alcohol content OF 6.99%, L. plantarum count of 7.08 log CFU mL^?1, polyphenol content of 34.46 mg/100 g, reducing sugars of 2.39% and a titratable acidity of 0.34%. Cassava and plantain beers were prepared using the optimized parameters of the rice beer experiments and the resultant beers exhibited the desired chemical parameters, suggesting applicability of the conditions to preparing these types of local beers from a wider range of substrates. Copyright © 2015 The Institute of Brewing & Distilling     

SYNTHESIS OF AROMA COMPOUNDS BY WORT ENTEROBACTERIA DURING THE FIRST STAGE OF LAMBIC FERMENTATION

Lambic is a special type of Belgian beer obtained by a spontaneous fermentation. The fermentation is initiated by a growth of enterobacteria and non-maltose fermenting yeasts. These organisms die off after one to two months. To gain a clear insight in the relations between the enterobacteria and the aroma compounds formed in wort during this first period, several bacterial isolates were studied with respect to their metabolites formed in a synthetic medium and in two different lambic worts, using aerobic or semi-anaerobic conditions. The results showed that enterobacteria, especially Enterobacter species, are responsible for the production of 2, 3-butanediol, acetic, lactic and succinic acid and lower amounts of ethyl acetate and higher alcohols which are the main aroma compounds found in 1 to 2 months old lambic. Ethanol production is mainly due to yeast activity. The results are in agreement with previous determinations of entero-bacterial species present in first phase lambic¹⁸ .     

Induction of Viable but Nonculturable State in Beer Spoilage Lactic Acid Bacteria

Strong beer spoilage strains Lactobacillus lindneri DSM 20692 and Lactobacillus paracollinoides JCM 11969^T were repeatedly subcultured in degassed beer and their culturability on MRS agar was examined. As a result, the two strains were found to show decreased culturability, suggesting that the prolonged contact with beer reduces the culturability of beer spoilage lactic acid bacteria (LAB). After 30 subcultures in degassed beer, both strains were subjected to sublethal heat treatment. As a consequence, L. lindneri DSM 20692 and L. paracollinoides JCM 11969^T were no longer detectable on MRS agar despite the presence of 460 viable cells, indicating that the viable but nonculturable (VNC) states were induced for both strains. Problematically, the heat treated VNC strains were shown to exhibit beer spoilage ability, suggesting that spoilage incidents can occur without detection by culture media. It was also shown that, once acquired, the VNC states are stably maintained in beer without further heat treatment. These results suggest the possibility that beer spoilage LAB strains remain hidden in pitching yeast and work‐in‐process products without detection. Furthermore L. lindneri DSM 20692 and L. paracollinoides JCM 11969^T in VNC states were successfully stored at ?80°C with 10% dimethyl‐sulfoxide as a cryoprotectant and reconstituted in degassed beer without losing VNC characteristics. Taken together, these findings show that valuable bioresources can be acquired from culturable beer spoilage LAB strains and maintained for long‐term storage as frozen culture stocks.     

Occurrence of glyphosate in beer from the Latvian market

A sensitive LC-MS/MS method for the determination of glyphosate in beer has been developed, validated, and applied to analyse 100 beer samples from 24 different producers and distributors in Latvia. The selected samples represented most beer brands and varieties sold in local supermarkets. Different procedures for sample preparation and chromatographic separation were compared. The final version of the method consisted of solid phase extraction, chromatographic separation on aminopropyl stationary phase, and detection using tandem mass spectrometry. The concentration of glyphosate in beer varied from below the LOD of 0.2 μg kg^?1 up to 150 μg kg^?1, higher than previously reported. Significantly higher (p < 0.01) content of glyphosate was observed in beers that did not have the country of production disclosed on the label and were sold in local supermarkets by distributors from Latvia (1.8 μg kg^?1 median concentration in locally produced beer, 6.7 μg kg^?1 in beer of undisclosed origin).     

LIBERATION OF STALING ALDEHYDES DURING STORAGE OF BEER

Trans-2-nonenal, 3-hydroxynonanal and 3-hydroxybutanal were isolated from barley and wort and mass spectral evidence for the presence of further hydroxyaldehydes was found. The concentration of free aldehydes in a model solution was found to decrease in the presence of bisulphite. Addition of acetaldehyde to a mixture of aldehyde bisulphite complexes released trans-2-nonenal in preference to other aldehydes. The concentration of sulphite in beer decreased by 66% over four months. This data was combined in a theory in which the papery, cardboard stage of beer staling is ascribed to a decrease in bisulphite concentration and subsequent bisulphite transfer from unsaturated aldehyde bisulphite addition complexes.