26 April 2017

Possibilities for Optimising Wort Preparation – Part 2

In the article cited, wort preparation can be calculated in terms of evaporation and re-formation; this property is used here for predicting possible improvements. The second part of this five-part series of articles on improving wort preparation revisits a problem discussed previously: what is the best process for driving off DMS from wort?

Efficient evaporation of DMS is a known and hotly debated issue. Process knowledge about the various evaporation processes has been published by Hertel at that time [1]. The result was: processes in which wort is depressurised from a higher pressure to a lower pressure are less efficient compared to the classic, directly heated pot. Important sub-questions have to be answered, taking account of the particular characteristics of a boiling system (temperatures, process control, volatility etc.). These considerations are expanded on below. For the first time, account is not just taken of evaporation from the various boilers, hot holding proceeding in the boiler systems and thus DMSP breakdown are also included. Depending on process conditions, additional assessments are possible. In the following, evaporation and hot holding are considered separately in external and kettle boiling systems.

DMS Evaporation and DMS Re-Formation

Various authors have explained and proved that DMS formation in the brewhouse can be calculated [2-5]. Their considerations are being used now in order to map processes and compare them. External boiling and kettle boiling serve as examples here. The first describes the wort flow through the heat exchanger and is found in many breweries in the form of external or internal boilers. The latter can be described using a pot as an example that is heated on a hot plate. Wort does not flow here but all wort is heated via the bottom or the walls of the container. Such directly heated systems are rare today but can still be calculated.

Evaporation of DMS from wort can be calculated for external and internal boiling and re-formation of DMS from DMSP can be predicted based on equations. Kettle boiling is an open copper having a temperature of about 100 °C throughout. In such an open process, boiling is efficient and DMS re-formation uniform under the conditions at 100 °C. External boiling continuously depressurises wort in the kettle. This is a closed process and – proven procedurally – less efficient that open boiling [1].