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Lactobacillus brevis is the most significant beer spoilage bacteria worldwide. It is found as a contaminant at all stages of brewing, including during primary and secondary fermentation, storage, filtration and the packaging process. In production with flash pasteurisation and subsequent hygienic filling, avoiding and tracing secondary contaminations is the key to a microbiologically stable product. However, L. brevis strains vary in their spoilage potential and can grow in many different beer types. This study presents a physiological test scheme for growth potential and biofilm formation in various media. It was determined that a large number of L. brevis strains can form biofilms as a first coloniser. The identification of the species alone is therefore not enough to be sure of the spoilage risk, which shows the need for a more in depth differentiation. DNA fingerprint techniques are crucial to differentiate isolates of this species at strain level. The rep-PCR fingerprint system (GTG) 5 was used to differentiate a selected collection of 20 isolates, which were characterised in growth and biofilm formation in various media. The data showed a high variation within the selected isolates. As second step, generated fingerprint clusters of L. brevis were traced back to contamination sources in a German brewery, revealing a high number of isolates with potentially varying growth, spoilage and biofilm potential. L. brevis being the demonstrator species, the PCR system used is a powerful and compatible tracing and troubleshooting tool for all kinds of spoilage bacteria in the brewing industry.

Derivative spectroscopy was used for quantitative determination of natamycin in cheese. When measuring a methanolic cheese extract against methanol, the second derivative of the UV-spectrum is measured between 340 and 290 nm. The natamycin concentration can be determined by measuring the vertical distance between the minimum at 318 nm and the maximum at 311 nm. Under these conditions the detection limit of natamycin in a pure methanolic solution lies at 20 ng/ml, in cheese extracts at 150 ng/ml. The latter corresponds to a natamycin concentration of 2.5 ppm in the case of a 3 g test sample or 0.03 mg/dm2 in the case of a 25 cm2 cheese surface. The introduction of derivative spectroscopy makes it possible to reduce the interference of cheese substances in the photometric measurements and to increase the sensitivity and selectivity of the detection process. Besides the advantage that work and expenses are reduced - as no pimaricin-free sample has to be extracted from the interior of the cheese - it is also possible to determine natamycin photometrically in cheese, in which it is distributed homogeneously.