DERIVATION OF A PROFILE METHOD FOR SENSORY ANALYSIS OF BEER FLAVOUR

Flavour assessment ultimately depends on sensory methods of analysis. Profile methods are considered to offer the best current solution to the problem of describing, and as far as possible quantifying, beer flavour. The sensory characteristics of flavour must be identified and described systematically and objectively, without prejudice due to preferences. A flavour ‘vocabulary’ is needed which is applicable to all types of beer. This involves selection of significant terms which have the same meaning for different people. Any system universally applicable to all types of beer must necessarily be complex, but such a “universal” system is essential for research. It also provides a “dictionary” from which terms can be selected for simpler profiles for quality control of particular products. The steps in the development of a profile system are described. Development has depended and will continue to depend on the collaboration of a large number of individuals and groups of people within the industry. Profile systems cannot be static but must continuously evolve.     

SENSORY QUANTIFICATION OF BITTERNESS AND FLAVOUR OF BEER DURING STORAGE*

Sensory techniques were utilized to measure bitterness and degree of liking for commercial lagers, and to quantify aroma and flavour qualities of two sets of experimental lagers. Significant negative correlations were obtained between sensory bitterness and degree of liking for 17 commercial beers, by inexperienced as well as by trained judges. Sensory bitterness was positively correlated with BU values, with both measurements negatively correlated with beer age. In experimental lagers, BU values decreased with increasing time and temperature of storage, but sensory bitterness, as determined by trained judges, decreased only with storage time. Increases in malty, ethanol, and skunky aromas with time of storage were accompanied by decreases in hoppy, musty, and wet cardboard aromas. Baked aroma increased sharply with increasing storage temperature. In a second set of experimental lagers varying in pH (3·7, 4·2, or 4·6) and/or headspace gas, sourness was markedly affected by pH whereas baked flavour was significantly stronger in beers with O₂ than in those with CO₂ headspace. The data are discussed in terms of differences between analytical and consumer-type sensory testing, and in terms of changes in aroma and flavour attributable to iso-α-acid content, pH, headspace gas, and time and temperature of storage.     

CHEMICAL CHARACTERIZATION OF DIFFERENCES BETWEEN ALES AND LAGERS

The chemical identification of the substances responsible for differences between ales and lagers has been investigated, using new as well as established techniques. The two types of beer are broadly similar in composition, but lagers are characterized particularly by higher levels of certain sulphur compounds, and ales by higher levels of certain heterocyclic compounds. Several compounds have been identified for the first time as beer components.     

PROFILE ANALYSIS AND FLAVOUR DISCRIMINATION

The relative merits of profile tasting and difference tasting are discussed. Profile analysis can reveal and characterize flavour differences that are not revealed by difference tasting using the triangular or three-glass test, even though the same people carry out both types of test. A multiple comparison test is used in conjunction with profile analysis to reveal the size as well as the nature of perceived differences in flavour. This is exemplified by studies of the effect of adding increasing amounts of diacetyl to three different types of beer. It may be necessary to consider not just the presence of individual flavour notes but also their duration and order of perception in order to explain the effects of flavour potentiators, such as guanosine 5′-monophosphoric acid.     

DIFFERENTIATION OF ALE AND LAGER FLAVOURS BY PRINCIPAL COMPONENTS ANALYSIS OF FLAVOUR CHARACTERIZATION DATA

The application of principal components analysis to flavour characterization data has been examined by comparing and contrasting 32 beer samples. These comprised two samples of each of 16 brands of beer selected to represent 4 different types, contrasting ales and lager beers of two different strengths. Two-dimensional plots of results using the first two principal components as axes showed resolution of the four groups of beers and the close proximity of the majority of the duplicate samples. Differences between samples thus revealed are in accordance with known differences between the beer flavours.     

THE INFLUENCE OF MASHING CONDITIONS ON WORT AND BEER QUALITY

From a comparison of the performance of ale and lager malts mashed by constant temperature infusion, by temperature programmed infusion, and by decoction procedures it emerges that malt modification and the pattern of kilning are as important in determining the composition of wort as are the mashing conditions. Worts with appropriate levels of amino and total nitrogen and of fermentable sugars may be obtained by selecting lightly-dried well-modified malts and mashing with a constant temperature infusion rather than by using less modified malt in conjunction with more complex mashing programmes. Ale malts yield worts of lower pH which is reflected in a slight reduction in hop utilization. Head retention is improved by the use of undermodified malts but colloidal stability is improved when well-modified malts are used. In the case of well-modified malts a high final curing temperature is not a prerequisite for achieving good colloidal stability in beer.     

THE INFLUENCE OF CONDITIONING ON LAGER BEER QUALITY

The relative contributions to lager beer quality of malt, conditioning, and other parts of the brewing process have been assessed by analytical and sensory evaluation. Backed beers, brewed and fermented under various conditions, were stored at temperatures of 12°C, 4°C or 0°C for periods ranging from 2 to 38 days before filtration and bottling. No evidence could be found to justify a need for long periods of beer storage. Although prolonged storage can provide a remedial process, correcting aspects of beer quality such as diacetyl levels, final gravity, and removal of ‘young beer’ flavour, all these features can be more rapidly, effectively and economically controlled by closer attention to materials quality and primary fermentation procedure.     

EFFECT OF WORT-EVAPORATION ON FLAVOUR AND OTHER BEER QUALITIES

Pilot scale trials have been carried out to determine the importance of evaporation during wort-boiling at atmospheric pressure. Using normal brewing materials It has been established that an evaporation of only 2% of the total volume of a wort is sufficient to produce beers of sound flavour. Further evaporation had no significant effect on the flavour or other qualities of the finished beer.     

PROCEDURE FOR NON-DESTRUCTIVE CONCENTRATION OF FLAVOUR-ACTIVE COMPONENTS OF BEER

New methods for the isolation and concentration of beer volatiles are described. Components with higher and lower volatility are treated separately. More highly volatile components are separated by vacuum distillation at low temperatures (below — 46°C) in a closed system. The resulting concentrates are conveniently stored in specially constructed ampoules. Beer components with low volatility are isolated by steam distillation of beer at below 20°C under vacuum followed by solvent extraction of the distillate. Solvent is removed at 0°C and the concentrate stored in ampoules. Both procedures avoid contamination during isolation and concentration and also avoid thermolysis or oxidation of components. The concentrates are obtained in a form particularly suitable for examination by gas chromatography and gas chromatography coupled with mass spectrometry.     

THE STALING OF BEER

It has previously been shown that unsaturated fatty acids must be considered as one class of precursors responsible for the staleness of beer. It is now demonstrated that oxidation products of carotenoids may also contribute to the stale flavour.     

PRINCIPAL COMPONENTS ANALYSIS-ITS APPLICATION IN MONITORING THE CONSISTENCY OF BEER QUALITY

The technique of principal components analysis is explained, and its application in monitoring the consistency of beer quality described. Product consistency may be monitored by making between-brand or within-brand comparisons, based on the results of instrumental analysis.     

TRYPTOPHOL,TYROSOL AND PHENYLETHANOL—THE AROMATIC HIGHER ALCOHOLS IN BEER

A gas chromatographic method is presented for routine quantitative analysis of aromatic higher alcohols in beer. A satisfactory overall order of reproducibility, sensitivity and simplicity was achieved under the conditions described. This method has been used to compare finished Canadian ales and lagers. It was possible to differentiate an ale from a lager fermentation by the tryptophol content of the product. Experiments were conducted to investigate the influence of several factors on the concentration levels of aromatic higher alcohols. These compounds are produced by the yeast during fermentation and the levels achieved depend upon the type of yeast used, the fermentation conditions, and differences in the wort fermented.     

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.     

DIMETHYL SULPHIDE AS A FEATURE OF LAGER FLAVOUR

Dimethyl sulphide is a normal flavour component of many lagers, particularly Continental lagers, but is not present in ales in sufficient quantity to affect flavour. The kilning stage of malting determines the extent to which a precursor capable of being converted to dimethyl sulphide by yeast will be present in wort. Worts prepared from Continental malts appear to contain more of this precursor than worts from British malts and the derived beers thus contain more dimethyl sulphide. Amounts of dimethyl sulphide formed from the precursor during fermentation depend on the strain of yeast employed, whilst the amounts retained in solution depend on physical factors such as temperature and rate of evolution of carbon dioxide.