Shelf Life Of Beer Research Articles

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.

Effects of high hydrostatic pressure on shelf life of lager beer

Filtered bright lager beer samples were either treated with high hydrostatic pressure (HHP, 350 MPa for 3 and 5 min at 20 °C) or conventional heat pasteurization (60 °C for 15 min). A storage period of 56 days showed that HHP and heat pasteurization had similar results in terms of pH and color (p<0.05). However HHP-treated samples had lower bitterness and protein sensitivity and higher chill haze values than the heat pasteurized samples at the end of the storage period. The microbiological stability of HHP-treated beers was the same as that of heat-treated beers, and the development of both lactic and acetic acid bacteria was inhibited for 56 days of storage. Although more studies should be carried out to investigate the effects of HHP treatment on different types of lagers and ales, our results revealed that HHP could be successfully used to increase the shelf life of beer even at temperatures well below those required for heat pasteurization.

Conventional and alternative principles for stabilization of protein and polyphenol fractions in beer

Beer haze is primarily formed through complexation of protein and polyphenolic beer ingredients. The problem of reducing susceptibility of beer haze formation can be done either by lowering protein and/or polyphenol levels, or by minimizing the molecular size of protein/polyphenols. In experimental part of this work the shelf life of unstabilized beer is being compared with beer stabilized with various standard products, such as PVPP and silica gel. Furthermore, the trials have been made to prove the functionality of a new product consisting of carrageenan and cross-linked PVPP. The method used to determine shelf life was haze forcing test (0/60?C). Extract, alcohol, bitterness, foam, haze, color and pH were also monitored. The test results showed expectedly that combined treatment of beer ensures the highest level of product stability. Through selective stripping of polyphenols and protein fractions it is possible to improve shelf life of beer to a significant extent.

Beer Polypeptides and Silica Gel Part I. Polypeptides Involved in Haze Formation

Beer contains approximately 500 mg/L protein depending on the brewing procedures employed. This protein is in the form of polypeptides, the majority of which lie within the 10–40 kD size range. Some of these polypeptides are responsible for causing colloidal haze, others enhance foam stability and the remainder appear to have no function in beer except to contribute to mouth-feel. The polypeptides responsible for haze formation are those that can combine with polyphenols to produce a visible cloudy haze. This is undesirable as it can have a negative effect on the beer's shelf life. One way to reduce this effect is to remove these polypeptides using silica gels. It is important that this removal is selective, and the desirable foam enhancing polypeptides are not removed. Data will be presented to show that beer polypeptides are glycosylated and that silica preferentially adsorbs glycoproteins, particularly those with protein components rich in the amino acid proline. The molecular size and composition of glycoproteins recovered from untreated beer, cooked adjunct, silica exposed to beer and beer aged for one year are presented. Glycoproteins involved in foam, and the apparently functionless polypeptides, will be discussed in a subsequent paper.

Studies on the Effects of Common Process Variables on the Colloidal Stability of Beer

The effect of simple changes in process variables on the colloidal stability of beer was examined. Lager beers were stabilized using silica hydrogel (SHG) at 25–125 g/hl or polyvinylpolypyrrolidone (PVPP) at 10–50 g/hl. The effect of storage time (up to six days) and storage temperature (0 and 4°C), before stabilization and filtration, on the resultant colloidal stability of the beers was examined. The results were used to optimize the stabilization process with respect to sorbent dosage rate and beer storage time. Haze precursors were measured using the standard rapid assays: tannoids, total polyphenols, total flavanols, sensitive proteins, and alcohol-chill haze. Colloidal shelf life was measured as the time taken to reach a total haze of 2 EBC units in weeks at 37°C or months (28 days) at 18°C. Colloidal shelf life was directly proportional to sorbent dosage rate for both SHG and PVPP. The rapid assays were poor predictors of beer shelf life but were effective monitors of the stabilization process. The optimum storage time examined for lager beer before filtration was three days. Increasing the storage temperature from 0 to 4°C could be compensated for, in terms of measured colloidal shelf life, by increased stabilizer dosage rate.

NISIN AND BREWING

Nisin, an internationally accepted food preservative has been shown to inhibit the growth of almost all Gram-positive beer-spoilage bacteria investigated. The initial effects on these bacteria appear to be upon the cell membrane. Nisin has little effect on most Gram-negative bacteria and has no effect upon the growth and fermentation properties of brewing yeasts. Nisin activity survives kieselguhr filtration, fining and pasteurisation and has no effect on beer shelf life. Nisin has potential applications in preventing spoilage of worts or beers by Gram-positive bacteria (particularly lactic acid bacteria).

Scope and Limitations of Enzymatic Deoxygenating Methods to Improve Flavor Stability of Beer

Flavor stability is increasingly becoming the limiting factor in shelf life of beer. Because deterioration of beer quality is closely related to oxidative changes—molecular or radical forms of oxyg...

Scope and Limitations of Enzymatic Deoxygenating Methods to Improve Flavor Stability of Beer

Flavor stability is increasingly becoming the limiting factor in shelf life of beer. Because deterioration of beer quality is closely related to oxidative changes—molecular or radical forms of oxygen are the major sources of aging flavor problems—complete elimination of the prime determinant, oxygen, would be expected to prevent off-flavors from developing during storage of packaged beer. To test this hypothesis, we used glucose oxidasecatalase to remove the oxygen from bottled beer. Surprisingly, although the enzyme system effectively removed oxygen, flavor was not efficiently stabilized. We demonstrate that the lack of correlation results from a rapid build-up of hydrogen peroxide, which is utilized by catalase for the coupled oxidation of ethanol and other oxidizable substrates in beer. A combined treatment with glucose oxidase and free sulfite largely prevented the peroxidative phase and almost completely suppressed oxidative reactions involved in flavor deterioration.