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September–November 2023

Tasting terroir – influence of barley malt flavour on beer

There is no disputing that ‘a beer drinker drinks as much with his or her eyes as with their mouth’.* The serving of beer in a well-selected glass also heightens the anticipation of beer quality attributes such as flavour, colour, clarity, foam and degree of carbonation, which the brewer crafts to meet or exceed that promise. The dispensed beer must also consistently meet or exceed the drinker’s expectations for style and brand.

Beer flavour must then fulfil the expectations arising from visual cues, as described above, which forms the opening lines of a recent paper (Stewart et al., J. Am. Soc. Brew. Chem. 2023, vol. 81, p. 282–98). This anticipated beer flavour is primarily influenced by malt kilning and the choice of yeast/hops in the beer recipe. Although barley malt is the material backbone of most beers, variety has until recently been largely overlooked with respect to flavour differences. Stewart and colleagues studied 11 malt variety samples from Australian and international (UK, Canada, China) growing regions, that were infusion mashed (65°C) at laboratory scale to produce unboiled wort, to investigate differences in flavour profiles determined by sensory assessment and headspace-solid phase microextraction gas chromatography–mass spectrometry.

Sensory evaluation identified wort flavour differences, with the control heritage samples, Maris Otter/Schooner, having the highest overall flavour complexity and acceptability (see graph). The Chinese-malted Chinese/Canadian samples ranked lowest for overall flavour complexity. Overall, 107 compounds (aldehydes, alcohols, esters, organic acids, terpenes, ketones) were found to vary among the varietal worts. The sensory assessment was supported by principal component analysis plots, with Maris Otter and the Australian samples clustering in different quadrants from the Chinese-malted Canadian/Chinese samples. Overall flavour complexity was correlated with Kohlbach index (protein modification), malt protein (negative) and ß-glucosidase (negative), while sweetness was correlated with limit dextrinase and pH.

In the last decade, several groups have sought to delineate the molecular basis for putative malt flavour differences in wort, whisk(e)y and beer. Although most malt flavour studies concentrate on differences between varieties, four investigations have considered the influence of the barley growing environment on beer flavour (Bettenhausen et al., J. Am. Soc. Brew. Chem. 2018, vol. 78, p. 136; Herb et al., J. Am Soc. Brew. Chem. 2017, vol. 75, pp. 345, 354; Li et al., Mast. Brew. Ass. Am. Tech. Quart. 2022, vol. 59, p. 74). In an extended study over two growing seasons in Canada, using four commercial varieties, Li et al. (2022) observed that despite significant differences for malt quality parameters (e.g. grain protein content, Kohlbach index), limited differences were observed for aroma and non-volatile beer compounds by sensory analysis or by mass and NMR spectrometry.

Terroir is a sparsely studied aspect of malt quality, despite it being an important component of wine marketing: the ‘sense of place’ imbued by terroir is an expression of the growing of a variety in a specific region with respect to local climate, soil, grape microbiome, vineyard elevation/aspect, and viticultural and winemaking methods. Similar corollaries to wine terroir can be drawn for the quality of malting barley.

Direct evidence for terroir in malting barley literature is more elusive and is mainly confined to recent malt flavour studies. The evidence in turn appears to be at least somewhat linked to grain protein content and Kohlbach index. Recently, Evans et al. (J. Inst. Brew. 2023, vol. 129, in press) observed that the primary terroir-influenced malt component is grain protein content, which in turn appears in part to be controlled by day length during grain maturation. In general, increasing day length typical of grain maturation in Australia tends to be associated with lower grain protein content, while decreasing day length during grain maturation tends to be associated with the higher protein contents typical of Canada. These insights link directly into the flavour relationships outlined in the graph above.

* Bamforth C.W. Euro. Brew. Conv. Monograph XXVII (Amsterdam) 1999, pp. 10–23.

Evan Evans is a malting and brewing research consultant as the Tassie Beer Dr in Tasmania.

Scatterplots between wort overall flavour complexity/intensity ranking and (A) malt protein, and (B) malt Kohlbach index. Malting barley varieties AC Metcalfe (Met) and CDC Copeland (Cop) were grown in Canada and malted in China, while Gan Pi was grown and malted in China. Compass (Comp), Commander (Com), Planet (Pla), Scope (Sco), Sparticus (Spa) and Westminster (Wes) were grown and malted in Australia, while Maris Otter (Mot) was grown and malted in the UK. Figure extracted from Stewart et al., J. Am. Soc. Brew. Chem. 2023, vol. 81, p. 282–98.

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