Home News PhD student develops quality grading system for honeybush tea

PhD student develops quality grading system for honeybush tea

Brigitte du Preez's dissertation focused on ways to describe and quantify the differences between honeybush tea brews in a way that improves quality control

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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 a high-quality brew of honeybush tea from a mediocre one? 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. She received her degree from Stellenbosch University’s department of food sciences during a recent graduation ceremony for the faculty of agrisciences.

Research supported by the ARC

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 Matie researchers are participating.

Her 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.

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

“Honeybush tea has a recognisable fragrant floral, apricot, caramel and fynbos-sweet aroma and sweet taste,” Du Preez explains. “Its characteristic sensory profile has been mapped and can be used in quality scoring of samples of different production batches of the tea.”

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Brigitte du Preez recently received her PhD degree from Stellenbosch University. Photo: Supplied
Brigitte du Preez recently received her PhD degree from Stellenbosch University. Photo: Supplied

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.

Sensory characteristics of tea

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.

She 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. intermediaC. subternata and C. genistoides) that are considered commercially important.

Stellenbosch PhD graduate Brigitte du Preez studied the sensory, colour and turbidity (clarity) analyses of 585 tea batches that represented high to poor quality teas. Photo: Brigitte du Preez/Supplied
Stellenbosch PhD graduate Brigitte du Preez studied the sensory, colour and turbidity (clarity) analyses of 585 tea batches that represented high to poor quality teas. Photo: Brigitte du Preez/Supplied

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.

The chemicals represent 23 aroma attributes of honeybush tea. A chemical is added to a base honeybush tea for evaluation of a specific honeybush aroma to train assessors in its “sensory language”.

Du Preez furthermore identified sensory classes and specifications for high, moderate, low and poor quality tea.

High quality represents premium quality tea and moderate quality represents the minimum standard for a consumer product. Low quality represents the minimum standard for batch blending, whilst poor quality represents the level at which the industry should reject batches.

“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,” 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.”

Du Preez’s grading system and supporting tools can now be used throughout the supply chain. These tools include a revised aroma lexicon and wheel that visually maps the aroma attributes of honeybush tea and their intensities, as well as a scorecard and colour reference card for ease of use in routine quality control. She also tested two rapid sensory methods for screening of a large number of tea batches.

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.

Honeybush tea is a South African herbal tea made from the leaves of the honeybush plant. It is grown on the Eastern Cape of South Africa and is closely related to rooibos tea. Photo: Supplied
Honeybush tea is a South African herbal tea made from the leaves of the honeybush plant. It is grown on the Eastern Cape of South Africa and is closely related to rooibos tea. Photo: Supplied

Also, the aroma references can help honeybush processors and marketers understand honeybush sensory vocabulary (such as “fynbos-floral”) and taint terminology (such as “medicinal” and “smoky”). This understanding will equip them to communicate unambiguously through means of these standardised terms, and simplify the sensory quality control process.

Finally, the new system and tools could also form a basis for regulatory control in terms of certification and export control.

Global demand for honeybush tea

Sensory quality control is critical to supporting the sustainable growth of the industry, 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.”

Honeybush tea is a South African herbal tea brewed from the fermented leaves and stems of the honeybush plant (Cyclopia spp.). It is named after the honey-like smell of its bright yellow flowers.

This endemic fynbos shrub grows naturally in the Western and Eastern Cape, in an area ranging from Piketberg to Port Elizabeth. There are currently 23 known species of honeybush in Mzansi. Approximately 350 tonnes of locally processed tea products were exported in 2019, including to countries such as South Korea and Japan.

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Staff Reporter
Staff Reporter
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