Beer Staling Research Articles

Determination of Furfural in Beer by High-Performance Liquid Chromatography with Solid-Phase Extraction

Furfural is a sensitive indicator of beer staling. A new solid-phase extraction (SPE) column PEP-SPE (Polar-Enhanced Polymer, 500 mg/6 mL) was used to develop a method for extraction of furfural from beer. The PEP-SPE column retains furfural with higher selectivity than the commonly used C 18 -SPE column. Satisfactory precisions were obtained with %RSD (n = 6) less than 2.2% for peak areas. Recovery rates were in the range of 99.7-100.1% due to the simple treatment and good resolution. The detection limit was 5 μg/L. Furfural concentration ranged from 10 to 32 μg/L in twelve fresh beer samples. A noticeable increase in furfural content was found after beer samples were kept at 35°C for seven days. The calculated correlation coefficient between taste panel scores for beer freshness and the furfural content of aged beer samples was -0.65, which showed a good inverse correlation between freshness marks and furfural content.

The Influence of Heavy Metal Ions on Beer Flavour Stability

: In this study, the importance of iron and copper ions and their radical formation via the respective Fenton and Haber-Weiss reactions was confirmed. Of the other heavy metals present in the brewing process in relevant concentrations, the impact of manganese ions on beer flavour stability has been elucidated. In contrast to iron and copper, manganese ions are not removed from wort or beer to any great extent during the process. Additionally, manganese shows a similar radical-promoting effect to that seen with iron and copper. Its reactivity, and typically higher concentration than the other two metals in beer, appear to make manganese an especially potent pro-oxidant in beer. The results of the investigation clearly indicate that there are other heavy metals influencing the stale flavour characteristics of beer, in addition to the well-known metals, iron and copper. In contrast to the aforementioned ions, manganese does not enter the product by being leached out of a tank or from piping materials, but rather comes from the cereals employed in brewing. This finding, concerning the importance of manganese as a redox system in beer staling, can serve as a basis for a different approach in the choice of raw materials.

The influence of wort aeration and yeast preoxygenation on beer staling processes

The influence of oxygen on the beer staling process is considered to be of major importance. Therefore, the impact of wort aeration, which is thought to cause wort oxidation processes, on beer ageing, has been examined. Pilsner and ale beers were produced with the classical wort aeration technique or by the use of the yeast preoxygenation process, in which yeast cells are exposed to oxygen before fermentation. The staling of these beers was studied using P&T GC–MS and sensory analysis. GC–MS analyses of the natural and forced aged beers showed no significant differences between the two treatments. Sensory evaluation of natural and forced beers confirmed these results. Thus, normal wort aeration (8 mg/l) does not appear to determine flavour stability in a direct manner. This is probably due to the short contact of the wort with oxygen at low temperatures before the onset of fermentation.

Identification of a Stale-Beer-like Odorant in Extracts of Naturally Aged Beer

For a long time, beer staling has been a prime concern in brewery research. Yet, to improve flavor stability, better knowledge of all chemicals involved is still needed. From our aroma extract dilu-tion analyses (AEDA) applied to naturally aged lager beers emerged an old-beer-like odorant at RICP-SIL 5 CB = 1532 and RIFFAP = 2809, with a FD value close to that of trans-2-nonenal (the well-known cardboard off-flavor found in aged beers). Specific phenol extraction, GC cold trapping, and mass spectrometry (electron impact and chemical ionization) enabled us to identify it as 4-vinylsyringol. Although already mentioned in some fresh beers, this compound had never been highlighted as involved in the aging process of lager beers.

Antioxidant Pool in Beer and Kinetics of EPR Spin-Trapping

The kinetics of spin-trap adduct formation in beer oxidation exhibits an induction period if the reaction is carried out at elevated temperatures and in the presence of air. This lag period lasts until the endogenous antioxidants are almost completely depleted, and its duration is used as an indicator of the flavor stability and shelf life of beer. This paper demonstrates that the total kinetics of the process can be characterized by three parameters-the lag period, the rate of spin-trap adduct formation, and, finally, the steady-state spin-adduct concentration. A steady-state chain reaction mechanism is described, and quantitative estimates of the main kinetic parameters such as the initiation rate, antioxidant pool, effective content of organic molecules participating in the chain reactions, and the rate constant of the 1-hydroxyethyl radical EtOH(*) spin-adduct disappearance are given. An additional new dimensionless parameter is suggested to characterize the antioxidant pool-the product of the lag time and the rate of spin-trap radical formation immediately after the lag time, normalized by the steady-state concentration of the adducts. The results of spin-tapping EPR experiments are compared with the nitroxide reduction kinetics measured in the same beer samples. It is shown that although the kinetics of nitroxide reduction in beer can be used to evaluate the reducing power of beer, the latter parameter does not correlate with the antioxidant pool. The relationship of free radical processes, antioxidant pool, reducing power, and beer staling is discussed.

Characterization of 9-Fatty Acid Hydroperoxide Lyase-Like Activity in Germinating Barley Seeds That Transforms 9(S)-Hydroperoxy-10(E),12(Z)-octadecadienoic Acid into 2(E)-Nonenal

Previously, we reported that 2(E)-nonenal, having a low flavor threshold (0.1 ppb) and known as the major contributor to a cardboard flavor (stale flavor) in stored beer, is produced by lipoxygenase-1 and a newly found factor named 9-fatty acid hydroperoxide lyase-like (9-HPL-like) activity in malt. To assess the involvement of 9-HPL-like activity in beer staling, we compared the values of the wort nonenal potential, an index for predicting the staleness of beer, with the lipoxygenase and 9-HPL-like activity of 20 commercial malts. There was a significant correlation between the malt 9-HPL-like activity and the values of wort nonenal potential (r=0.53, P<0.05), while the correlation between malt lipoxygenase activity and the wort nonenal potential was statistically insignificant. Analysis of the partially purified 9-HPL-like activity from embryos of germinating barley seeds indicated that 9-HPL-like activity consisted of fatty acid hydroperoxide lyase and 3Z:2E isomerase.

Multivariate Modeling of Sensory and Chemical Data to Understand Staling in Light Beer

To identify beer chemistry changes during staling in light beer, an attempt was made to model analytical chemistry data with sensory data using multivariate statistical methods on samples subjected to various time-temperature treatments. Standard beer analyses were completed on these light beer samples in addition to using an in-house gas chromatographic method to profile carbonyl development during staling. Trained sensory panelists evaluated these packaged beer samples following standard descriptive methods and rated a total of 31 attributes, of which 12 flavor and aroma attributes related to staling were selected for modeling. Projection to latent structures (PLS) algorithms were employed on the data to model the 48 known and 41 unknown carbonyl compounds to these 12 mean sensory scores. The known compounds found to be significant indicators of light beer staling from the PLS models were 2-furfural, acetal, 5-hydroxymethyl-2-furfural, t,t-2,4-hexadienal, dihydro-5-pentyl-2(3H)-furanone (γ-nonalactone), t,t-2,4-decadienal, and 1-heptanol. Conversely, compounds that loaded negatively in the PLS models for staling were furfuryl acetate, ethyl hexanoate, 1-heptyl acetate, and ethyl octanoate (i.e., these esters decrease during staling). In addition, several unknown peaks loaded both positively and negatively with beer staling in the PLS model. This PLS methodology may prove to be a useful tool for understanding which compounds drive staling in certain beers. In our models, light beer staling displayed a dual mechanism in which known unpleasant stale compounds increased at the same time that known pleasant fruity esters decreased.

Factors Affecting 5-Hydroxymethyl Furfural Formation and Stale Flavor Formation in Beer

5-Hydroxymethyl furfural (5-HMF) and furfural are index compounds for beer staling. A correlation exists between the organoleptically determined degree of staling flavor in beer and 5-HMF levels during storage. This suggests that controlling 5-HMF formation during brewing might provide useful clues for improving the flavor stability of beer. Various experiments performed to control the levels of 5-HMF show that active oxygen and low pH in a finished beer enhance the formation of 5-HMF during storage. Using antioxidative mashing and selecting yeast strains with higher cellular volume are effective, practical methods for regulating these levels. Cell sizes of yeast strains (calculated from photographic images of about 100 cells) were found to correlate with the beer pH levels produced by those strains. Using pitching yeast with a larger cell size resulted in a higher pH level of beer and a lower level of 5-HMF.

Investigations of the Protective Mechanism of Sulfite Against Beer Staling and Formation of Adducts with Trans-2-Nonenal

Development of stale cardboard flavor in beer is believed to be associated with liberation or formation of the unsaturated aldehyde trans-2-nonenal, known as an oxidative breakdown product of linoleic acid. During fermentation, brewer's yeast produces sulfite. This naturally produced sulfite— or sulfite added after fermentation—has been shown to contribute to the flavor stability of beer. The present investigation was set up to more closely examine adduct formation between trans-2-nonenal and sodium bisulfite. Three different chemical adducts have been synthesized and characterized by 1H NMR spectroscopy and LC-MS. Formation of adducts in aqueous buffer at beer pH was confirmed indirectly by 1H NMR spectroscopy and directly by LC-MS.

Nonoxidative Mechanism for Development of Trans-2-Nonenal in Beer

Oxidation is usually recognized as the major cause of development of a stale flavor in beer. However, no significant difference in trans-2-nonenal concentration has been observed between oxygen-receiving and oxygen-free beers after aging. Moreover, 18O2 was not incorporated into the carbonyl fraction, indicating that the cardboard flavor in beer is not due to lipid oxidation in the bottle. As shown by adding deuterated nonenol to the pitching wort, nonenal oxidation and sulfitic adduct degradation were also inefficient pathways of trans-2-nonenal synthesis. On the other hand, wort nonenal linked to amino acids and proteins revealed to be able to release nonenal at the beer pH. The measured nonenal potential proved a good indicator of beer staling; therefore, UV spectroscopy was used to find which experimental conditions destabilize trans-2-nonenal precursors in wort. Laboratory-scale experiments confirmed that SO2 can reduce both lipid autooxidation and the nonenal potential rise while the wort is boiling.

A STUDY OF BEER STALING USING CHEMILUNINESCENCE ANALYSIS

The chemiluninescence (CL) analysis has been used to study beer staling. Several types of commercial Japanese beers were stored at 37°C and their CL development analysed at 60°C. The CL level in beer developed as the beer was stored to reach a maximum level and then decreased. The sum of the CL intensities for the first 1 hour showed a good relationship with staling degree as assessed in mean panel scores. It is postulated that the deterioration rates of beers might be assessed from the CL producing patterns in the fresh beers before storage. The presence of sulfite in beer depressed the CL production during its storage indicating that there is some contribution of sulfite to flavour stability due to its inhibitory effect on radical reactions in beer.

Flavor Stability

The formation of trans-2-nonenal is one of the main causes of beer staling. The main mechanism contributing to the generation of trans-2-nonenal in beer is the enzymatic or nonenzymatic oxidation of lipids and oxidized free fatty acids. This hypothesis has been examined by looking for relations between lipoxygenase activity in malt, nonenal potential in wort, and nonenal values in fermenting wort and beer in relation to the sensory flavor stability of the finished beer. New methods were developed to determine nonenal potential and trans-2-nonenal values. It was concluded that within one experimental series of brews, lipoxygenase activity and nonenal potential were useful to predict susceptibility of beer to staling. Moreover, there was a high degree of correlation between nonenal potential and trans-2-nonenal developed in beer after natural aging. A test in which three oxidation products of linoleic acid, all suspected precursors of trans-2-nonenal in beer, were added to beer, did not give evidence of whether these components were precursors or not. Other aldehydes, besides trans-2-nonenal, were formed that do not appear during natural or forced staling of beer. In fermentation trials with an excess of trans-2-nonenal in wort, rapid reduction of trans-2-nonenal to a nondetectable level was demonstrated. At the same time, 2-nonen-1-ol and 1-nonanol were formed. Different crown corks showed remarkable differences in the diffusion velocity of oxygen through the plastic liner. The choice of a liner with a low diffusion velocity leads to a lower oxygen content and thus better flavor stability of the finished beer during storage. Finally some suggestions are given for the reduction of staling.

The Role of Free Radicals in Beer Oxidation

The relationship between free radicals and the staling of beer was studied. Hydrogen peroxide was generated when beer was incubated at 60° C. When examined by electron spin resonance spectroscopic ...

The Role of Free Radicals in Beer Oxidation

The relationship between free radicals and the staling of beer was studied. Hydrogen peroxide was generated when beer was incubated at 60° C. When examined by electron spin resonance spectroscopic analysis, the hyperfine splitting constants of phenyl-tert-butylnitrone adducts of beer incubated at 60° C with H2O2 were close to those of beer without H2O2. The production of aldehydes and the degradation of isohumulones during the incubation of beer were accelerated by the addition of H2O2 or by irradiation with γ-rays. They were inhibited by the addition of ethylenediaminetetraacetic acid. It is suggested, therefore, that H2O2 generated during the incubation of beer could interact with the metals present to play an important role in radical reactions in beer.

Ethylene Production in Staling Beer

ABSTRACTLevels of ethylene in the headspace of three brands of staling lager beers which were allowed to stale at 40°C increased with storage time. TBA values and browning of staling beers also increased with storage time and coincided with increase in ethylene production. Results indicated that measurement of ethylene in the headspace of beer might be useful to follow beer staling.

New Procedures to Improve the Flavor Stability of Beer

Palliatives for enhancing the stability of beer flavor have been evaluated by organoleptic tests, but primarily by use of an accelerated aging technique, followed by estimation of staling substances using thiobarbituric acid (TBA). TBA has also been used to trace the quantities of carbonyl compounds and their precursors through malting and brewing and in beer treated with palliatives and substances that cause flavor deterioration. Beer staling is reduced by scavengers of the hydroxyl radical (mannitol, ascorbic acid) and is increased by agents which elevate hydroxyl levels (e.g., peroxide/ metals). Staling substances develop during malt kilning and wort boiling, but primarily during fermentation. There is evidence that soybean extracts enhance the shelf life of beer flavor if included in the fermenting wort; we suggest that this action is caused by superoxide dismutase. Procedures for making soybean preparations devoid of lipoxidase include heating and soaking beans in ethanol. However, doubts are cast upon the role of lipoxidase in staling.

New Procedures to Improve the Flavor Stability of Beer

Palliatives for enhancing the stability of beer flavor have been evaluated by organoleptic tests, but primarily by use of an accelerated aging technique, followed by estimation of staling substances using thiobarbituric acid (TBA). TBA has also been used to trace the quantities of carbonyl compounds and their precursors through malting and brewing and in beer treated with palliatives and substances that cause flavor deterioration. Beer staling is reduced by scavengers of the hydroxyl radical (mannitol, ascorbic acid) and is increased by agents which elevate hydroxyl levels (e.g., peroxide/ metals). Staling substances develop during malt kilning and wort boiling, but primarily during fermentation. There is evidence that soybean extracts enhance the shelf life of beer flavor if included in the fermenting wort; we suggest that this action is caused by superoxide dismutase. Procedures for making soybean preparations devoid of lipoxidase include heating and soaking beans in ethanol. However, doubts are cast upon the role of lipoxidase in staling.

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.

Contribution of Hop Bitter Substances to Beer Staling Mechanisms

Ethyl esters of isovaleric and 2-methyl butyric acids form in bottled beers and contribute to stale sensory characteristics. Previous research suggests that these acids, together with isobutyric ac...

Contribution of Hop Bitter Substances to Beer Staling Mechanisms

Contribution of Hop Bitter Substances to Beer Staling Mechanisms