Lesson 5 - Wort Boiling Technology and Process Control SAQ

** In terms of design and operation, how can internal and external calandrias be optimised? Use examples of commercially available technologies to illustrate your answer.

Response:

Internal calandrias are limited in size due to the need for them to fit in the kettle. Optimisation in terms of design is therefore limited to modification of the wort spreader, tube diameter and addition of pumped flow. Let’s start from the top. The wort spreader can be designed to deflect wort at different heights to work with different phases of boiling. The Krones Stromboli uses an upper deflector when operating with pumped flow to reduce foaming and the lower deflector during conventional boiling to provide a large surface area for removal of volatiles. The spreader on the GEA Jetstar® deflects wort at two levels which is designed to achieve both criteria. In addition, it has an aperture under the wort surface that can be opened or closed. During the thermal phase of the boil, the aperture is open and the wort flows from the calandria back into the wort, below its surface. This is designed to improve wort mixing and reduce thermal load.

The Krones Stromboli features a pump which circulates the wort, reducing the thermal load required to move the wort. The pumped flow is fed into a venturi where wort is entrained resulting in rapid and turbulent flow through the calandria. This increases heat transfer inside the calandria and when the wort leaves the calandria, it provides excellent removal of volatiles.

The Ziemann Holvrieka Shark internal calandria has two tube sizes that enable different modes of boiling to be achieved. The tubes towards the centre of the calandria are narrow and the tubes towards the outside are wide. The narrower tubes increase thermosyphon producing high flowrate and turbulence, improving heat transfer and reducing thermal load.

Many calandrias are only controlled to boil wort at a specific evaporation rate. Steam flow and pressure are the only means of regulation. All three of the calandrias above are controlled to split boiling into phases where thermal processes like trub formation and conversion of SMM to DMS are maximised and phases where evaporation of volatiles is maximised. Using this approach means that less thermal energy needs to be supplied to achieve the objectives of boiling. And good quality wort can be produced from lower percentage evaporation. 

Unlike internal calandrias, external calandrias can be as large as required. The Briggs Symphony external calandria has a very large heating surface area compared to older external calandrias. It also has a greater number of long heater tubes than earlier designs. This results in a lower difference in temperature between the steam and wort, so minimises negative effects on both foam and flavour stability. The low ΔT also reduces fouling, allowing more brews to be completed between CIPs. Both a large surface area and a low ΔT help produce large numbers of vapour bubbles. This promotes nucleate boiling, improving trub formation and volatile stripping. A standard EWH does not achieve this as effectively.

During the boil, the wort is returned to the kettle above the liquid surface, at a tangent. This improves wort homogeneity and gives the option of using the vessel as a kettle whirlpool. The Symphony reduces energy demand due to its improved volatile stripping, which means we need lower total evaporation for the same volatile removal.