South African researchers have developed a flavour and mouthfeel wheel that provides 27 descriptive attributes for Rooibos tea as a tool to facilitate communication among producers, processors, grading experts, marketers, flavour houses, importers and consumers.
Many of us have taken a sip of tea and immediately been able to distinguish the taste as either good or bland, without being able to say why. In order to go beyond simplistic distinctions and to properly discern the great many tastes and aromas that give rooibos tea its flavoured nuances, South African researchers have developed a flavour and mouthfeel wheel for the unique homegrown brew.
The novel wheel provides 27 descriptive attributes for rooibos – 20 flavour and seven taste and mouthfeel descriptors – and will be a practical tool to facilitate communication among rooibos producers, processors, grading experts, marketers, flavour houses, importers and consumers.
The wheel is the work of a team including Ilona Koch, a Masters student at Stellenbosch University. Under the leadership of Professor Elizabeth Joubert of the Agricultural Research Council, (who designed the project proposal together with Stellenbosch University lecturer Ms Nina Muller), Koch and a team of researchers have spent over a year compiling data through numerous experiments with rooibos tea.
“This study was conducted to characterise and quantify the sensory attributes associated with rooibos flavour (taste and aroma) and mouth-feel to paint a more comprehensive picture of what is frequently referred to as ‘typical’ or ‘characteristic’ rooibos flavour,” said Koch.
The researchers studied 69 different rooibos samples originating from 64 different plantations in various production areas. These samples had been graded from A to D, representing the highest to the lowest tea quality respectively.
A strict protocol was followed when brewing the tea – 300g of boiling, deionised water was poured onto 5.8 g of dry tea leaves, which was infused for five minutes. The tea was strained and stored in a stainless steel thermos flask to keep the temperature constant, and 100 ml of tea was served to each taster in a white porcelain cup covered with a plastic lid to prevent evaporation and loss of volatiles. The tea cups were preheated in an oven set to 70°C, and kept in water baths with the temperature regulator set at 65°C throughout the sensory analysis session.
Nine judges took part in the study, selected on availability and interest. “Most of them had extensive experience with descriptive analysis of a wide range of products. None of them, however, had previous experience with sensory analysis of rooibos,” said Koch.
During the first training stage the panellists were exposed to a number of rooibos samples to become familiar with the product and the evaluation protocol. During 22 one hour sessions, the 69 samples were analysed and compared to one another, and the panel generated aroma, taste and mouth-feel terminology.
Some 85 aroma and 38 taste and mouthfeel descriptors were generated at this stage, but this proved to be too large a field of data for the efficiency necessary to produce the wheel. The number of descriptors was subsequently reduced to eight aroma descriptors and nine taste and mouth-feel descriptors. A score card was developed which showed each of these 17 descriptors together with a 10cm unstructured line scale ranging from “none” to “prominent”.
After training was over, the panel used the score card to rate the intensity of the 17 attributes for each of the 69 samples during 40 sessions spread out over eight weeks.
Through the research, it was uncovered that the positive sensory characteristics such as floral, woody, honey and sweet could be separated from the negative attributes such as green plant, hay-like, dusty and sour. In light of this, the descriptors were grouped according to the positive or negative impact on the quality of the sensory experience.
While the research delved into a number of experiments to deduce specific data including the effect of steam pasteurisation, the effect of particle size and the oxygen radical absorbance capacity of rooibos (ORAC), the flavour and mouthfeel wheel represents the attributes of unpasteurised rooibos infusions.
The wheel will be further updated and refined with samples from another season during the three-year project, which will run until March 2012. It is being funded by the SA Rooibos Council and the Technology and Human Resources for Industry Programme (THRIP) that aims to boost South African industry by supporting research and technology development.
Now drinking tea will no longer be about whether it’s simply good or average, but a sensory experience akin to the tasting of wine where you will be able to indulge in the subtle tannins and fine distinctions in taste and aroma that rooibos infuses into each of its products.
Professor Elizabeth Joubert
Agricultural Research Council
Phone: +27 21 809 3444 – Fax: +27 21 809 3430