Studies on taste stability of beer

The change in the beer aroma substances that occur during beer ageing were studied by means of the new developed analysis of carbonyle (purge and trap technique, GC/MS with SLM) and the optimised method of water vapour distil lation and methylene chloride extraction as well as initially also using th e analysis of the N-heterocycles and compared to a sensory ageing tasting t echnique developed by the authors. A series of aroma substances demonstrate a clear relationship between the ageing taste and their concentration. Thi s means that the following nine aroma substances can be regarded as indicat or components and in turn they were influenced by the prevailing temperatur e ("W") and the oxygen content ("S") or by the ageing in the course of the storage time ("A"). These indicators are the following: Nicotinic acid ethylester (A, W), 2-furfural (A, W), 3-methyl-butanal (A, S ), gamma-nonalactone (A, W), phenylethanal (A, S), benzaldehyde (A, S), 2-m ethyl-butanal (A, S), 2-methyl-butane-2-one (A) and heptanal (W). Apart fro m heptanal, the aroma components were recorded as totals using the factors "W", "S" and "A" in the form of indicator substances. The weighted tasting and the total of the ageing components of 44 beers and over 300 reserve spe cimens showed a correlation of r = 0.736***. This value was r = 0.978*** fo r material from a single brewery. Nevertheless, it is not possible to produ ce guide and limit values for these indicators to assess the absolute agein g condition of a beer. The initial concentrations in fresh beer fluctuate t oo greatly in terms of raw materials and technology for this. In addition, the indicator substances have no effect on taste as a result of their high taste threshold values (with the exception of gamma-nonalactone). On the ba sis of the results of the studies, the negative factors on taste stability were placed in three outline groups: Technological effects: Increase oxygen absorption in the brewhouse increase d 2-pentanone, heptanal and octanal. Beers from non-floated worts showed in creases in 2-furfural, 2-methyl-butanal, 3-methyl-butanal and phenylethanal . Effects caused by oxygen absorption from the storage tank to sealing the bo ttle: Oxygen absorption increased phenylethanal, benzaldehyde and 2-methyl- butanal. CI Effects caused by distribution such as movement, storage temperature, stora ge duration and light: High storage temperatures produced a clear increase in nicotinic acid ethylester, 2-furfural, -nonalactone and heptanal. Exposure to Light caused a light taste in green bottles that cannot be regi stered by analytical methods. The change in the aroma substances followed t he factors of temperature and time. Movement produced poorer results in the lasting, the quantity of ageing substances increased.