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Predicting Haze Stability in Wheat Beer using Light Scattering Analysis Techniques
C. Schwarz, M. Zarnkow, W. Back, T. Becker

Visible and intense turbidity is seen as a defining characteristic of German and Belgian wheat beers. To date, no reliable method has been established for predicting the haze stability of wheat beer. It would be very beneficial for breweries to be able to predict haze stability so as to ensure that the beer retained a satisfactory level of haze during its shelf life. To predict wheat beer haze, trials were undertaken, in which light scattering analysis techniques and particle size distribution measurements were made, for the purpose of characterizing the haze stability of wheat beer. The wheat beer samples assessed had substantial differences in haze stability durability, from 19 days up to more than 160 days, as judged by when 90 scatter light intensity drops bellow 30EBC units. Interestingly, the classification of all samples by the 90:25 ratio of scatter light intensity showed values from 0.5 up to 1.0 and it was observed that as haze stability increases, the ratio expressing the intensity of light scattering at 90:25 also increases. Particle size distribution measurements showed for samples with high 90:25 ratios of scatter light intensity (>0.9) had monomodal distributions with high ratios of particles <1m which was favourable indicator of beer haze durability*.A pronounced amount of haze is typical for German and Belgian wheat beer styles and therefore represents an important quality attribute. This is quite the opposite that brewers require for their bright or non-turbid beer styles that conventionally make up the majority of the beer market [1]. The rising popularity of these naturally cloudy beer styles has necessitated that they possess an extended shelf life as well as prolonged haze stability. This is to ensure that when a customer purchases the beer that at least a satisfactory level of haze is evident on dispense. However, predicting the haze stability of wheat beer is still difficult, because reliable method has yet to be developed. As part of these trials, bottled wheat beers were tested using light scattering analysis techniques and particle size distribution measurements. The intensity of scattered light at fixed angles by spherical particles can be expressed using the dimensionless parameter x based on the MIE theory [2]: Equation where d is the diameter of the particle and the wavelength of the light. The parameter x for particles between 0.11m at a wavelength of 500nm is between 0.626.2, and for particles with a diameter of 5m (e.g. yeast cells), it is approximately 31. For all MIE parameters, forward scattering (< 90) generally increases as the angle decreases. The absolute intensity of scattering increases with particle diameter [3].

Descriptors: Wheat beer, haze, haze measurement

BrewingScience Monatsschrift fr Brauwissenschaft, 64 (Juli/August 2011), pp. 68-74