LIQUID CO2 AND ETHANOL EXTRACTION OF HOPS PART III- EFFECT OF HOP DETERIORATION ON UTILISATION AND BEER QUALITY

The quality of beers bittered with liquid CO₂ and ethanol extracts derived from fresh and deteriorated hops and the percentage utilization of alpha-acids therefrom were comparable. The importance of using analytical methods which measure bitterness substances per se is emphasized.     

Consumer rejection threshold for 1,8-cineole (eucalyptol) in Australian red wine

The compound 1,8-cineole is known to elicit the perception of eucalyptus flavour. There is debate over whether eucalyptus flavour is positive or should be considered a taint in red wine. The current experiment measured a consumer rejection threshold (CRT) in red wine, using samples spiked with increasing concentrations of cineole. Results estimated the CRT in red wine at 27.5 ppb. Analysis of a post-experiment questionnaire suggested that preference for cineole is not significantly influenced by gender, age, level of experience or prior experience, though these results were based on a small sample. Results suggest that a moderate intensity of eucalyptus character in red wine should not be considered a taint and that some consumers may consider moderate intensities preferable to no eucalyptus character. The CRT determined allows quantitative decisions to be made in response to measured levels of cineole in red wine. Winemakers and wine marketers considering promoting eucalyptus character as a taste dimension in wine now have a quantitative basis on which to be guided.     

Physico-chemical characterisation of a non-conventional food protein source from earthworms and sensory impact in arepas

This study aimed to characterise a non-conventional protein source: a powder made from earthworms, and to evaluate its potential use as human food. The way it was prepared led to low solubility and wide particle size distribution. Sensory analysis was used to assess the acceptability and the organoleptic properties of maize-based pan-cakes fortified with this novel protein powder. Satisfying products were obtained with a substitution level of 5.5% (w/w) earthworm powder in pan-cakes. GC-MS allowed the identification of more than seventy volatile compounds that may be responsible for the off-odour of the powder. The most abundant chemical groups found in the volatile fraction were ketones with undecan-2-one, alcohols with pentan-1-ol, and aldehydes with hexanal. Partial delipidation was tested as a way to improve the organoleptic quality of the powder. It clearly led to less intensely coloured samples but delipidation must be optimised to have an impact on odour.     

DIMETHYL TRISULPHIDE,ITS MECHANISM OF FORMATION IN HOP OIL AND EFFECT ON BEER FLAVOUR

The precursor of dimethyl trisulphide (DMTS) in hops is destroyed by sulphur dioxide during kilning, but then re-forms slowly during storage. A redox mechanism is suggested and S-methyl-cysteine sulphoxide is postulated as the DMTS-precursor. The effect of DMTS on beer flavour is described. The flavour threshold value for DMTS in a commercial beer has been found to be 0·10μg/litre.     

ON THE SUNSTRUCK FLAVOUR OF BEER

It has been confirmed that sunstruck flavour is due to the formation of 3-methyl-2-butene-1-thiol formed by photolysis of iso-α-acids in the presence of sulphur-containing amino acids.     

ESTIMATION OF NUCLEOTIDES IN BEERS AND THEIR EFFECT ON FLAVOUR

Low concentrations of nucleotides have been shown to be present in different types of beers using a microbead anion exchange chromatographic system. Taste trials have demonstrated that over 6 ppm of a flavour-modifying nucleotide must be added to beers to produce a significant alteration in flavour. As beers have been found to contain less than a twentieth of this value it has been concluded that nucleotides occuring naturally in beers do not contribute significantly to flavour.     

NUCLEOTIDES IN BEER

Nucleotidic material was isolated by anion exchange chromatography of beer on a Dowex 1 × 8 (formate) column. Ultraviolet spectroscopy and retention volume data suggested the presence of cytidine monophosphate (CMP) [max. 5 mg/litre], in one of the fractions. No other mononucleotides were detected. Chromatography of charcoal extracts of beer on DEAE Sephadex A25 failed to yield a fraction containing mononucleotides. Triangular taste tests indicated that addition of adenosine-5′-monophosphate (AMP) and guanosine-5′-monophosphate (GMP) to beer (30 mg/litre and 25 mg/litre respectively) did not cause significant flavour changes.     

Effect of organic vapour interaction on permeation rate through polymer films

The permeability coefficients (P) of linalool, citral ethyl butyrate, d-limonene and octanal permeating through LDPE and ionomer films were measured alone as individual and as a component of a mixture at a temperature of 23 °C and in saturated water vapour. Values of P for ionomer film were approximately two orders of magnitude below those for LDPE for the compounds tested. Both PET and PETG films were found to be much better barriers against the compounds tested than LDPE and ionomer films. In general, the permeability, diffusion and solubility coefficients (P. D, and S) values measured in mixture were substantially less than the values obtained individually. Permeability behaviour of these compounds at low concentrations in the mixture was similar to that of permanent gases. Reduction of solubility coefficients in mixture permeation was greater with the higher solubility coefficients. These results provide a better understanding of the mechanism of vapour diffusion through polymers.     

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.