24 August 2017

Possibilities for Optimising Wort Preparation – Part 4

Wort preparation is at the heart of beer production, yielding wort for fermentation from water, malt and hops natural raw materials. The fourth part of this series of publications provides an ultimate answer to the issue of the best process for removing DMS from wort.

Parts 1  to 3 of  this series describe ways in which existing wort preparation units can be operated under optimal conditions to drive off DMS. It emerged that increasing the wort volume flow through the boiler is advantageous, all other parameters remaining equal. In Part 4, optimised boiler operation is described, showing that external boiling is superior to kettle boiling for DMS reduction.

Optimisation Measures

External boiling may be improved by ingenious variation of circulation and evaporation rates. The advantage associated with external boilers (increased re-formation) has to be emphasised in the process and the disadvantage associated with external boilers (inferior evaporation) has to be mitigated. This can be done by controlling circulation and evaporation rate.

The boiling process has to be subdivided into two phases. Circulation rate is drastically lowered in the first phase, resulting in higher re-formation in the external boiler. Circulation rate is considerably increased in the second phase, resulting in the correction factor of depressurising evaporation

ωi = 1 with good approximation and thus optimised evaporation. Evaporation rate has to be kept low but constant over both phases.

Fig. 1 is explanatory for the fact that this process is superior to kettle boiling with re-formation at the same evaporation rate. The overall DMS level over time is plotted for both boiling principles. The blue curve shows kettle boiling, the red curve shows external boiling. The graph illustrates that external boiling is superior to kettle boiling when operating as described. This can be attributed to the two phases selected.

At the beginning of the process, re-formation in the external boiler is more pronounced in phase 1 because (exaggerated for the purpose of exemplification) the low circulation rate through the boiler significantly raises temperature. At the end of this phase, here after 30 minutes, almost all DMSP has been converted in the external boiler. This is not the case in kettle boiling. Though more DMS has been driven off, DMSP is still present on account of the lower temperatures in the kettle.