Dugulin, Celina Angela
(2021)
Brewing with green malt for an energy and water efficient process: challenges and opportunities.
PhD thesis, University of Nottingham.
Abstract
The malting process can be separated into three key steps: steeping, germination and kilning – the latter being the most energy intensive step accounting for ~78% of the total energy demand. Naturally, the kilning process becomes the main point of interest to reduce the maltings energy footprint. Furthermore, malting and brewing involve sequential wetting and drying steps. Viewed solely from an energy and water use perspective these processes make little sense. Brewing beer using ‘green’ (germinated, but not dried) malt, could be a solution to making the malting industry more energy and water efficient. Such a process would reduce substantial energy input associated with kilning and conserve the water contained in the green malt. However, brewing with undried malt represents very disruptive technology and multiple aspects need to be considered to successfully brew with this ‘novel’ grist material (Dugulin et al. 2021; doi: 10.1080/03610470.2021.1902710). The overall aim of this project was to demonstrate the feasibility of brewing with green malt and propose solutions to some perceived technical and biochemical (flavour) barriers.
Early research was dedicated intensively to laboratory scale development to enable this alternative to conventional brewing processes. We investigated key quality concerns associated with green malt: lipoxygenase (LOX) activity, S-methyl methionine levels, development of oxidation products and rootlet removal (Dugulin et al. 2020; doi: 10.1002/jib.602). The results formed the basis for subsequent pilot scale brewing trials at KU Leuven. Here the aim was to compare between key quality parameters of worts and beers made from green malt and kilned malts (prepared from the same batches of green malt). 100% green malt was used in these experiments both as a technical challenge and to emphasise any impacts on key quality factors. Samples were taken throughout the green malt brewing process. These samples were then compared with wort and beer samples produced from a kilned lager malt produced from the same batch at the maltings. Here it was demonstrated that beers without significant taints or obvious defects can be brewed directly from green malt without prior removal of rootlets However, further technological and process optimisations are undoubtedly required (Dugulin et al. 2020; doi: 10.1002/jib.620). Furthermore, the results demonstrated promising indicators for flavour stability in brews using untreated green malt. Therefore, the focus of the subsequent study was to elucidate the flavour stability impacts of brewing with green malt. This was important to establish because reduced heat load could either improve flavour stability (reduced pool of staling aldehydes) or worsen it (since, e.g., lipoxygenase activity is regulated by heat treatment during kilning). The results showed that fresh beers from kilned (pilsner-style) malt resulted in similar concentrations of free staling aldehydes compared to green malt beers. This was surprising, as staling aldehyde concentrations in the kilned malt and particularly at the onset of the brewing process were significantly higher. Nevertheless, these aldehydes might bind to other compounds forming non-volatile adducts. The current theory is that during beer storage, under specific conditions (temperature, pH value, redox potential, binding strength, thermodynamic stability), adducts may dissociate and release aldehydes in the free form. Thus, forced ageing of beers was required to predict the flavour stability of a beer (style). Additionally, the oxidative stability of the wort and beer samples were determined using EPR spectroscopy at the University of Copenhagen. Results revealed that worts and beers produced from untreated green malt had a significantly better oxidative stability than the reference kilned malt beers. Lastly, to identify the beer chemistry changes during staling, beers were subjected to ageing at 30°C for 30, 60 and 90 days. An increase in concentrations of undesirable staling aldehydes and a decrease in concentrations of desirable compounds was noted in all beers. Interestingly, the results showed that green malt beers were less susceptible to beer ageing flavour change than kilned malt beers, due to a lower formation, or release, of staling aldehydes. Overall, results showed that green malt worts and beers could have a potential advantage in terms of flavour stability of the beer, provided lipoxygenase activity can be controlled by applying lipoxygenase hostile mashing conditions (pH 5.2; >63°C; oxygen free).
Brewing with green malt is a disruptive technology and the process needs to be further optimised before it could be implemented in present day breweries. Nevertheless, this research proved that wort and beer without any flavour defects and a very promising flavour stability metrics can be produced from 100% green malt with intact rootlets.
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