M-46: The impacts of steam injection technology upon volatile formation and stripping during wort boiling

C. P. HOLMES (1), W. Hense (2), D. Donnelly (3), D. J. Cook (1); (1) University of Nottingham, Loughborough, U.K.; (2) Diageo, Dublin, Ireland; (3) International Yeast Solutions, Dublin, Ireland


Over recent decades increasing fossil fuel prices have necessitated the development of novel and energy-efficient technologies for the brewing industry, in particular with regard to the most energy-intensive steps of the process, such as wort boiling. In this trial, one such technology, the Pursuit Dynamics PDX wort heater, was evaluated in full-scale brewing trials against an external wort boiling system to determine potential impacts on key quality attributes of wort and finished beers. A PDX wort heater (consisting of five PDX reactors) was retrofitted into a 1 million hL brewery in Ghana alongside the current external wort heater. The Pursuit Dynamics PDX wort heater injects culinary-grade steam into reactor chambers through annular nozzles. Upon entering the reactor chambers the wort is broken into small droplets, creating a vapor phase, which results in a multiphase flow and a claimed increase in energy transfer efficiency. Because the technology works through steam injection it differs from conventional boiling in that there is not a net reduction in wort volume (evaporation) across the boil. For this reason, it was of particular importance to check the volatile stripping efficiency of the technology and to determine whether it brought about changes in the volatile flavor composition of finished beers. The concentrations of selected wort volatile compounds were tracked across the boil, utilizing both traditional boiling (external wort heater) methods and the PDX wort heater, during the full-scale manufacture of three products (a lager, a stout and an unfermented malt beverage). Volatiles were analyzed by both solvent injection GC-MS and SPME GC-MS. Furthermore, the flavor composition of the final beverages in-pack were analyzed and compared between the two wort boiling technologies. Results indicated that the PDX wort heater had a relatively minor effect upon wort volatile composition, with furfural, 2-phenylethanal, 2-phenethyl alcohol, and dimethyl sulfide showing similar rates of formation and stripping compared with the control boil for the lager and stout worts. Both technologies produced worts of acceptable specification that were reasonably matched between trial and control brews, notwithstanding the lower steam usage, and thus energy savings for PDX brews. The stripping efficiencies of linalool, beta-myrcene, hexanal, and n-hexanol were somewhat reduced in the PDX trial brews. However, analysis of the packaged products revealed that after downstream processing analytical and sensory flavor differences between standard boil and PDX trial beverages were minimal.

In 2009, Calum Holmes received a B.S. degree in microbiology with virology from the University of Leeds, U.K. In 2010, he joined the University of Nottingham Brewing Science group, where he later qualified with a master’s by research degree in brewing science, the topic of which was “The Composition and Ultrastructure of Sorghum Spent Grains.” Continuing at Nottingham to study for his Ph.D. degree (2011–2015), Calum’s present research is focused on improvements to the sorghum brewing process.

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