Tribology of malt-based beverages: development and application of method

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Fox, Daniel
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University College Cork
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Soft tribology, i.e. the measurement of friction as a function of speed between two compliant surfaces, has found applications in food science and there is a growing body of theoretical and practical knowledge of fundamental mechanisms of lubrication as well as increasingly strong correlations between tribology and sensory data. Soft tribology is generally conducted using either commercially or in-house built tribometers however, the recent decade has seen a rise in the use of rheometers with tribology attachments. Based on current literature, knowledge gaps and potential avenues for future research have been identified. These include investigations on hydrophobicity of surfaces, surface wear (running-in), cleaning procedure of the attachment and tribopairs, speed (range and method of increase/decrease) and measuring system configuration. In the current research, frictional parameters of 10 beers (5 alcoholic and their non-alcoholic counterpart) were measured using an Anton Paar MCR301 rheometer with a tribology attachment (BC12.7, Anton Paar, Graz, Austria), and a range of variables was extracted and subjected to dimension reduction analysis (Principal Component Analysis, clustering, and correlation analysis). Sensory data consisting of a numeric mouthfeel rating and written reviews from an online beer-rating website ( were compiled, transformed, and correlated with the tribology data. Based on Frictional parameters of the beers, clear differences were observed between alcoholic and non-alcoholic beers, as well as those beers with high or low mouthfeel rating. Text-mining and clustering of the written reviews led to the development of 7 overall sensory descriptors; "watery", "smooth", "thick", "bitter", "foam", "astringent", and "sour", related to mouthfeel. Frictional parameters related to the static (speed range ~10-8-10-5 m/s), boundary (speed range ~10¬-5-5*10-5 m/s) and beginning of the mixed regime (speed range ~5*10-5-10-4 m/s) were correlated with "watery", "smooth", and "thick", while "bitter", "foam", "astringent", and "sour" were represented later in the mixed regime (speed range ~10-4-10-3 m/s). These results are significant in two ways; firstly, they indicate the usefulness of online beer reviews as a means to gather reliable sensory data, and secondly, they demonstrate tribology as a tool to instrumentally define and determine important mouthfeel parameters of beer. Further research is needed to fully validate this methodology; results from the online database should be compared to the outcome of a consumer panel under controlled settings, and a wider range of beers of different styles should be tested to fully understand the correlations between sensory phenomena and frictional parameters.
Tribology , Malt-based beverages , Non-alcoholic beer
Fox, D. 2021. Tribology of malt-based beverages: development and application of method. MRes Thesis, University College Cork.