Previous sensory analyses of rooibos (Koch et al., 2012) focused only on profiling rooibos produced in the Western Cape region during the 2009 production season. Since potential variation introduced by production season and production area was not taken into account, further investigation was deemed necessary to validate results. As already indicated, for the present study the sample set was expanded to include several production seasons (2011 – 2013), as well as rooibos produced in the Northern Cape region in addition to that produced in the Western Cape region.
The initial analysis was conducted using discriminant analysis (DA). This multivariate technique has a dual function, i.e. classification and separation; however, in research DA is mostly used for its classification function (Lawless & Heymann, 2010). Within the DA plot, three clear groupings were formed from the full set of samples (2011 – 2013). The split, as indicated in the results, was based on the production season and not the production area. This leads to the conclusion that the production season plays a greater role in the final sensory profile of the rooibos than the production area. There are a number of factors that may be responsible for these differences, including climatic differences, seen mainly by changes in the temperature and rainfall patterns from year to year (Archer et al., 2009). Joubert et al. 2012) demonstrates differences in the phenolic composition from year to year. The differences between the climatic conditions of the two production areas seem to play only a minimal or negated role in the sensory profiling of the rooibos, when compared to the yearly climatic changes. Changes in climate, whether it is a decrease or increase in rainfall or the presence of extreme events (droughts), are already having a significant effect on the crops in this area (Gérard, 2010). The climatic changes occurring in both the rooibos producing regions will not only influence the yields of the crops, but possibly also the quality of the final product. Initial research has shown that UV affects the accumulation of phenolic compounds (Schreiner, et al., 2012) and water stress can lead to an increase in flavonoids (Hernández et al., 2006). It is vitally important that these climate changes and the effect thereof on rooibos yield and ultimate product quality and sensory profile be researched further.
After testing the comprehensive sample set, the present study indicated that “rooibos-woody” aroma and flavour, “fynbos-floral” aroma and flavour, “honey” aroma, “sweet” taste and “astringent” mouthfeel were present in 100% of the samples, irrespective of the region of origin. The “astringent” attribute, when present in high intensities can have a negative impact on the quality of rooibos, however, when not detectable, the infusion is found to be insipid, therefore when present at a mild intensity, it adds
to the characteristic profile of the tea. “Hay/dried grass” notes were present in 90% to 100% of the samples from both regions and at differing intensities. The attribute “hay/dried grass” is definitely viewed by industry as a negative attribute (Personal communication, workshop with industry to validate the rooibos sensory wheel, 21 November 2013). However, when present in lower intensities, e.g. at intensities below 15/100, this negative attribute could possibly be viewed as not having a negative impact on the overall profile of rooibos. This view should, however, be tested for validity.
Sub-profiles, also emerged from samples collected in 2012 and 2013, indicating that regardless of the production area, “caramel” or “fruity-sweet” aroma was present in more than 40% of the samples. “Apricot” aroma was also found to be present in the sub-profile, although sometimes in a lower intensity and percentage occurrence than the “caramel” and “fruity-sweet” aromas. As indicated in the results, there are significant associations between these attributes for both production areas. The attributes found in 100% of the rooibos samples, from both production areas, therefore are indicative of the primary characteristic profile of rooibos tea. The primary characteristic profile is thus “rooibos-woody” and “fynbos-floral” notes, with a “honey” aroma, “sweet” taste and an “astringent” mouthfeel, often coupled with the slight flavour or aroma of “hay/dried grass”. The sub-profile lends itself to the occurrence of a secondary characteristic profile for rooibos tea. This secondary characteristic profile includes the “fruity- sweet” and “caramel” aromas, often combined with an “apricot” aroma. With the exclusion of the WC11 and NC11 samples, as they were not tested for all aroma attributes, the data set for 2012 and 2013 sufficiently represents the variation over production areas and production seasons. Most of the Northern Cape samples (61.4%) fall under the primary characteristic rooibos profile, whereas only 14.45% represent the secondary characteristic profile. The Western Cape samples represent the primary profile with 57% of the samples, and 9.35% of the samples fall under the secondary profile. These values are similar to those obtained for the samples from the Northern Cape, although slightly lower in value. In order to be considered as a match to the different rooibos profiles, the samples needed to exhibit the intensities of the attributes, within certain criteria. For the primary characteristic profile, the samples needed to contain the “rooibos-woody”, “fynbos-floral” and “honey” aromas at an intensity of more than 30, 20 and 15, respectively. For the negative attributes, they all needed to be present at an intensity of less than 10, whereas “hay/dried grass” needed to be below an intensity of 15. The secondary characteristic profile adhered to the same rules for the negative attributes, as for the primary profile. Additionally, the secondary characteristic profile required that the “apricot”, “fruity-sweet” and “caramel” aromas all be present at an intensity of greater than 10. If all the criteria were met, then the sample was added to the respective profile group, either primary or secondary. The samples that did not meet all the criteria for each of the profiles, were not labelled as having either a prominent primary or secondary characteristic profile.
Overall, samples harvested during the same production season, regardless of the production area, exhibited similar intensities for the sensory attributes. No distinct differences between the regions were
observed; leading to the conclusion that plant growth within either rooibos production region, does not affect the sensory profile of rooibos. Therefore, the development of production region-specific sensory wheels is not justified for the rooibos industry.