A new analytical parameter, the aniline index (AI), has been introduced for determining thermal stress exposure of pale lagers. Determination of the AI is relatively straightforward. A rotary evaporator and a spectrophotometer are the only instruments required.

Relatively short-term thermal influences (hot filling, flash pasteurisation, pasteurisation) can be picked up in beer by determining the reduction or absence of certain enzymic activities. When evaluating longer term or intensive thermal effects (e.g. forced staling), apart from sensory methods, quantitative determination of thermal indicators (e.g. 2-furfural, gamma-nonalacton) can be considered, using chromatographic methods, after suitable preparation of beer samples (e.g. 1).6 cm).

The physiological state of the yeast and the quality of green beer in the yeast suspension do not remain unchanged during yeast propagation under aerobic conditions. The priority objective should therefore not be related to the highest achievable propagation rates. An extensive test series in a pilot fermenter was carried out with the objective of optimising the process.

Many production units have started to use propagator technology for aerobic propagation of pitching yeast in recent years. Numerous authors (1, 2, 3, 4, 5, 6, 7) have detailed the advantages associated with this technology, as compared to conventional, batch-wise propagation under low-oxygen conditions.5 - 4, propagation factors of 15 - 20 can be achieved when using aerobic propagation technology.

In recent years, many different regimes for aerobic yeast propagation have become established in breweries. Mode of aeration, mixing of contents and suppression of foam account for the major differences in the various systems offered by suppliers. When designing a yeast propagation plant, very different aspects often play a part. In any case, top priority should be given to an optimal yeast crop. Planning and design of a plant for aerobic yeast propagation must thus take account of the needs of the yeast.

It is well known that Ca-oxalate precipitates act as crystallisation nuclei. Carbon dioxide is set free at these nuclei, this may contribute to gushing of beer and may also reinforce this phenomenon. This article describes factors promoting formation of Ca-oxalate crystals and the possibilities of taking preventative measures.

Calcium has a special significance when it occurs together with oxalic acid and can form with the latter calcium precipitates (Ca-oxalate) in beer. In addition to the accepted factors such a fusaria infestation of barley or malt, also referred to as "malt-based" gushing, or excessive iron concentrations in bottled beer, these Ca-oxalate precipitates are regarded increasingly as possible contributors to gushing. 3).

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