PhD student develops valuable quality grading system for honeybush tea

Tea lovers recognise a good cup of honeybush tea when they drink it: It has just the right aroma, colour and taste on the palate... but how do you distinguish high quality versus mediocre brew tea?

And, how do you describe and quantify the differences between brews in a way that improves quality control in the supply chain, from crop to cup?

Brigitte du Preez focused her PhD study on these questions, and received her degree from Stellenbosch University (SU) last week, after completing her studies in the Department of Food Sciences (Faculty of AgriSciences).

Dr Du Preez’s dissertation is titled “Development of a quality grading system for the honeybush (Cyclopia spp.) tea industry.” Her study forms part of the Agricultural Research Council’s research on honeybush tea, in which SU researchers are participating.

Dr Du Preez’s research shows it is possible to provide a sensory “quality seal” for different batches of tea. The sensory qualities of honeybush tea – including its aroma, appearance and taste – are crucial in distinguishing between high- and poor-quality tea products, she says.

“Honeybush tea has a recognisable fragrant floral, apricot, caramel and fynbos-sweet aroma and sweet taste,” Dr Du Preez explains.

“Its characteristic sensory profile has been mapped and can be used in quality scoring of samples of different batches of the tea.”

The honeybush tea industry has rapidly grown over the past two decades from a local cottage industry to a participant in the global herbal tea trade, one of the fastest developing segments of the hot beverages industry.

But there is tough competition in the market, and some challenges to overcome in expanding the industry’s market share.

Until now, there was no standardised set of measures to evaluate the sensory aspects of honeybush tea. Commercial processors, packers and marketers all use different ways to assess and communicate the sensory quality of the tea.

South African government regulations also do not specify sensory standards for honeybush tea. As such, tea of variable quality is released onto the market.

Dr Du Preez’s work could help address some of these challenges. She developed a user-friendly, quick and reliable quality grading system on the basis of input from role-players in the industry. This novel system provides a scientific way to evaluate and describe the sensory characteristics of different tea batches.

Dr Du Preez used a large dataset as a foundation for her research. This dataset was compiled from the sensory, colour and turbidity (clarity) analyses of 585 tea batches that represented high to poor quality teas.

She focused her efforts on three honeybush species (C. intermedia, C. subternata and C. genistoides) that are considered commercially important.

Dr Du Preez developed universal chemical-based reference standards to replace the food-based reference standards in the aroma lexicon of honeybush tea. This lexicon is a standardised descriptive vocabulary that describes the sensory characteristics of the tea.

“High-quality honeybush tea has a reddish-brown colour, a high intensity of floral, fruity and sweet aromas, with sweetness and some astringency on the palate,” Dr Du Preez explains. “Poor quality tea is characterised by an insipid overall sensory character on the palate, high intensities of taints, including ‘smoky’, ‘medicinal’ and ‘musty’ flavours.”

The novel application of these methods in sensory quality control would aid tea packing companies in the rapid assessment of tea for batch blending purposes, as well as researchers involved in honeybush plant cultivation. The new system and tools could also form a basis for regulatory control in terms of certification and export control.

Sensory quality control is critical to supporting the sustainable growth of the industry, Dr Du Preez believes. “It is also needed to ensure that good tea quality is not forfeited during the breeding of ‘superior’ plant material within research.

“As demand for honeybush tea grows, all production batches should meet optimum quality standards. Only quality batches should reach the market,” she said.