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Engineering investigations of the vapour-liquid-equilibrium of flavour-components at atmospheric wort boiling conditions (98.1 - 99.0 C)
Hertel, M., Scheuren, H. Sommer, K., Glas, K.

An important function of the boiling of wort is the evaporation of unwanted flavours. If the over-all evaporation is not sufficient, off-flavour will occur in beer. Furthermore, a decrease in the flavour stability can be recognised. The needed total evaporation to undershoot a required concentration of a flavour component at a given primary concentration in wort is given by the vapour-liquid-equilibrium (VLE) of the component and wort, respectively water. If the VLE of a flavour component is known, it is possible to calculate residue curves. In the case of wort boiling, these residue curves give a relationship between the percentage decrease of a flavour and the percentage evaporation of wort. Because of this, it is possible to calculate a needed over-all evaporation if the VLE, the required concentration of a compound at the end of boiling, and the primary concentration of the compound in the kettle up wort are known. For this, the VLE-diagrams of the most important flavours in pure water were acquired in this work. In contrary to the boiling of a mixture of flavour compounds in pure water, where no recreation takes place, it is in the case of boiling wort also necessary to know the recreation of the considered flavour compounds. Because of this, the rate constants of the same compounds that were investigated in this work, were measured in a former article. The recreation of a flavour depends only on the boiling temperature and boiling time. Thus, the results of the former article can be combined with the results of this article in terms of residue curves, if the evaporation rate is known. This calculation will be given in a follow up article in this journal.

Descriptors: Wort boiling, vapour-liquid-equilibrium, flavour-components, flavour stability

BrewingScience - Monatsschrift fr Brauwissenschaft, 59 (January/February 2006), pp. 16-20