Flavour change

Pasteurisation can affect the flavour of beer and Pasteur himself had concerns about the effects of pasteurisation on beer (Pasteur, 1876)  

To preserve bottled beer from deterioration, some bottlers employ, at the moment of filling, a small quantity of bisulphite of lime [calcium bisulphite]. Others heat the bottles to a temperature of55°C (131 °F) in the north of Germany and in Bavaria, this practice has been widely adopted since the publication of the author s Studies on Wine , and some of M. Velten s writings. The process has been termed pasteurization in recognition of the author s discovery of the causes of deterioration in fermented liquors, and of the means of preserving such liquors by the application of heat. Unfortunately this process is less successful in the case of beer than in that of wine, for the delicacy of flavour which distinguishes beer is affected by heat, especially when the beer has been manufactured by the ordinary process. 

A more recent study (O Connor-Cox, Yiu, Ingledew, 1991a) has described the detrimental effects of pasteurisation  

Perhaps the worst effect may be the off-fiavours accompanying the processing. Pasteurization flavour has been described as oxidized, bread crust-like, or possessing a cooked quality. These off-fiavours have been shown to be associated with a wide range of carbonyl compounds including unsaturated aldehydes. Prolonged pasteurization and/or exposure to oxygen have both been 

If oxygen is present, pasteurization generally also results in darkening of beer color. 

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Enzymatic maceration, which is a softening of plant tissue by the use of enzymes, has some potential quality advantages over mechanical-thermal disintegration as maceration is obtained with less damage to the cell walls. The major part of the plant cells remains intact by enzymatic maceration [25], as the enzymes attack only the space between the cells, and with only rare injury to the cell membrane [26]. The intact cells protect nutritional components within the cells which minimise flavour changes and deterioration on storage [27,28]. 

Table 21.6 Overview of chemical interactions responsible for flavour changes...

Cocoa beans are roasted between 140 and 180°C in roasters heated by steam or gas. The internal temperature of the beans must not be higher than 130°C. Roasting time is from 30 to 50 minutes. The water content of the bean is reduced to 1.5-2.5% during this process, its colour and flavour change, the pH-value is reduced and the husk is loosened. 

S.4.3.3 Physical and Chemical Flavour Changes during Processing and Shelf-Life... 

Stabilization against non-biological haze and flavour change (see Chapter 22). 

The application of heat can affect the flavour of beer in a number of ways, particularly if oxygen levels are high. Nevertheless, with good practice and attention to quality control a high-quality product can be produced with minimal flavour changes and a high degree of microbial stability. 

Rare decays are important in providing information about interactions not dominant under ordinary conditions. Rare lepton decays involving flavour changes are thus sensitive to interactions that go beyond the SM. 

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