What’s the Tea? – Tribology and International Tea Day

Here at PCS Instruments we have a deep appreciation for the great British beverage – tea! At first glance, the worlds of high-tech tribology and a comforting cuppa might seem miles apart, but if you take a deeper look you’ll find that tribology plays a significant role in enhancing our understanding and enjoyment of tea.

As it is International Tea Day – and as proud tea-drinkers – we’ve explored how tribology and rheology (the science of the flow of matter) intersect with the taste, sensation and flavours of tea. This tea-riffic article aims to shed light on how tribology can help quantify sensory perceptions, and will hopefully bring you a new-found appreciation in enjoying this ancient beverage.

Tea is the favoured drink of Britons, with an estimated 10 million cups of tea being made every day in the UK! But despite tea’s popularity, its relationship to tribology may not be obvious at first. Where tribology and tea meet is in oral tribology and rheology.

Oral tribology is focused on the interaction between oral surfaces and the foods or beverages consumed, and is closely related to rheology in understanding the sensory experience of tea drinking. While rheology is concerned with the flow and deformation of tea as a fluid, oral tribology specifically focuses on how this fluid behaves within the mouth, particularly how it interacts with the tongue and oral tissues.

This interaction, once quantified, provides insights into the perceived smoothness or roughness – a key component in experiencing astringency.

Astringency

Astringency is a sensory characteristic of certain food and drinks, like tea and red wine for example, that creates a dry, rough feeling in the mouth or throat. This sensation is largely due to tannins and catechins, types of polyphenols found in tea leaves, which interact with the proteins in saliva.

In foods that are high in tannins – like tea – the astringency is typically linked to the ability of tannins to bind with salivary proteins, which forms aggregates in the mouth. This binding can disrupt the protective salivary film of the mouth, increasing oral friction and exposing the mouth’s inner surfaces to these aggregates. [1]

The level of astringency in tea can vary a lot, for example tea varieties like oolong are far less astringent than black teas. Roasting tea leaves can reduce their polyphenol (a category of plant compound known to be astringent) content, and adding milk can also help as it binds to the tannins and reduces astringency.

The importance of tribology testing

As oral tribology increases in importance and popularity as a research area, more investigations into tea have been forthcoming. This includes research into the effects of plant-based milk on astringency and friction[2], the correlation between sweet aftertaste (Huigan) perception and friction coefficients[3], and even venturing into research on the abrasion rates of dental implants like Y-TZP by teas and coffee![4]

Tribological testing is essential in the food and beverage industry because it offers insights into how products interact physically with consumers, influencing both preference and health outcomes.

  • Influence on Consumer Preferences: The texture and mouthfeel of tea, such as the creaminess of milk alternatives or their astringency, are key factors that can affect consumer preferences. Tribological testing helps manufacturers understand these properties by measuring the friction these liquids create against oral surfaces. A higher friction level can indicate a less smooth texture, which might be perceived as less pleasant. By quantifying these characteristics, manufacturers can adjust formulations to improve the sensory appeal of their products, potentially increasing their marketability.
  • Correlation with Sensory Perceptions: Tribological testing also plays a role in correlating physical properties with sensory perceptions, such as aftertastes and overall mouthfeel. For example, a tea that leaves a smooth feeling in the mouth might also be associated with a pleasant aftertaste, encouraging longer sipping and potentially a higher consumer rating. Understanding these correlations allows producers to refine their products to enhance desirable traits, making them more appealing to the target audience.
  • Impact on Dental Health: Beyond taste and texture, tribological testing is crucial for evaluating how tea interacts with dental materials. Regular consumption of certain drinks can lead to abrasion of dental surfaces or restorations. By assessing how tea can affect different dental materials – such as those used in fillings or implants – tribological studies can help in selecting materials that withstand wear while maintaining aesthetic appeal.

We hope our insights into the role of tribology and rheology in tea appreciation have shed light on how deeply these sciences influence our tea experiences. By examining how tea interacts with our senses, tribological testing proves invaluable.

It not only helps manufacturers refine their offerings but also enhances the consumer’s enjoyment of a good cup of tea. Through tribology, each sip can open up a complex variety of sensations, enriching our understanding and appreciation of every kind of tea. So, happy international tea day, hope you enjoy your daily cuppa!

References

[1] M. A. Pires et al., (2020), “Sensorial Perception of Astringency: Oral Mechanisms and Current Analysis Methods”, Foods, Vol. 9, no. 8. (Available online: 10.3390/foods9081124)

[2] P. Cranwell, “Astringency of Tea and the Impact of Plant-Based Milk”, Centre for Industrial Rheology. (Available online: bit.ly/4dlBbZm)

[3] P. H . Chong et al., (2019), ““Oral” tribology study on saliva-tea compound mixtures: Correlation between sweet aftertaste (Huigan) perception and friction coefficient”, Food Research International, Vol. 125. (Available online: https://doi.org/10.1016/j.foodres.2019.108642)

[4] S. Sharifi and M. M. Stack, (2013), “A comparison of the tribological behaviour of Y-TZP in tea and coffee under micro-abrasion conditions”, Journal of Physics D: Applied Physics, Vol. 46, no. 40. (Available online: bit.ly/3JGgA4h)

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