The science behind Rooibos: What the latest research says

This is a summary of various studies on the sensory, industry and agricultural potential of Rooibos:

Phenolic content of Rooibos
The phenolic content of Rooibos is affected by seasonal production variations, quality grade and steam pasteurisation. Researchers found that grade A (the highest quality) samples contained a higher content of almost all phenolics. They also determined that steam pasteurisation decreased the content of the majority of phenolic compounds in a ‘cup-of-tea’ strength Rooibos infusion.
Stanimirova et al., 2013. High-dimensional nested analysis of variance to assess the effect of production season, quality grade and steam pasteurization on the phenolic composition of fermented Rooibos herbal tea. Talanta, 115, pp.590-599.
Available at: http://linkinghub.elsevier.com/retrieve/pii/S0039914013005237

Compound contributing to taste of fermented Rooibos
Scientists have isolated and analysed a compound thought to contribute to the taste and mouthfeel of fermented Rooibos. The compound is known as Z-2-(b-D-glucopyranosyloxy)-3-phenylpropenoic acid (PPAG) and it has a slightly bitter to astringent taste. It was not always present in high enough quantities to detect in unfermented tea leaves, and this leads to large variation in the fermented plant material, infusions and food-grade extracts.
Joubert et al., 2013. Occurrence and sensory perception of Z-2-(b-D-glucopyranosyloxy)-3-phenylpropenoic acid in Rooibos (Aspalathus linearis). Food Chemistry, 136, pp.1078-1085.
Available at: http://www.ncbi.nlm.nih.gov/pubmed/23122165

Impact of season and quality grade on polyphenols and antioxidants in Rooibos
Researchers found substantial variation in the polyphenolic content and total antioxidant capacities of different production seasons and quality grades of Rooibos.
Joubert et al., 2012. Variation in phenolic content and antioxidant activity of fermented Rooibos herbal tea infusions: Role of production season and quality grade. Journal of Agriculture and Food Chemistry, 60(36), pp.9171-9.
Available at: http://www.ncbi.nlm.nih.gov/pubmed/22920220

Rooibos sensory wheel and lexicon
This article describes how a sensory wheel was developed to help standardise the terminology and quality of Rooibos tea. Using the wheel, Rooibos teas can now be thoroughly described in terms of taste, flavour and mouthfeel. As such, the “characteristic” Rooibos flavour is described as “a combination of honey, woody and herbal-floral notes, with a slightly sweet taste and subtle astringency”.
Koch et al., 2012. Sensory characterization of Rooibos tea and the development of a Rooibos sensory wheel and lexicon. Food Research International, 46(1), pp.217-228.
Available at: http://linkinghub.elsevier.com/retrieve/pii/S0963996911006715

Higher antioxidant capacity of infused Rooibos tea
This study found that the total antioxidant capacity of infused Rooibos tea was slightly higher than that of Rooibos hot water extracts. The total polyphenol and aspalathin contents were equivalent, while the isoorientin and orientin contents of the infusion were found to be slightly higher than those of the extract. Hot water extracts are increasingly used as an ingredient in ready-to-drink beverages and a variety of food products.
Joubert, E. & De Beer, D., 2012. Phenolic content and antioxidant activity of Rooibos food ingredient extracts. Journal of Food Composition and Analysis.
Available at: http://www.sciencedirect.com/science/article/pii/S088915751200052X

Steam pasteurisation of Rooibos reduces polyphenols
Steam pasteurisation significantly reduces the amount of certain polyphenols in Rooibos, including the antioxidant aspalathin. It also affects the aroma and flavour of the tea, and decreases the astringency slightly.
Koch et al., 2012. Impact of steam pasteurization on the sensory profile and phenolic composition of Rooibos (Aspalathus linearis) herbal tea infusions. Food Research International.
Available at: http://linkinghub.elsevier.com/retrieve/pii/S0963996912004280

Summary of health benefits of Rooibos
This review article summarises the scientific data available on the health effects of Rooibos, including the animal models used and whether the tea was fermented or unfermented. The long list includes activities against cholesterol, high blood sugar, fat cell development, oxidative stress, heart disease, inflammation, wrinkles, cancer, sun damage and liver damage. The paper also mentions that Rooibos is actually not a valuable source of nutrient minerals like Vitamin C and iron, as is sometimes claimed in promotional material.
Joubert, E. & De Beer, D., 2011. Rooibos (Aspalathus linearis) beyond the farm gate: From herbal tea to potential phytopharmaceutical. South African Journal of Botany, 77(4), pp.869-886.
Available at: http://linkinghub.elsevier.com/retrieve/pii/S0254629911001086

Rooibos as an indigenous food crop adapted to growing conditions in Africa
The success of Rooibos highlights the potential of indigenous, multi-purpose food crops to alleviate poverty in Africa through income-generating produce, because such crops are well adapted to harsher African growing conditions.
Sprent, J.I., Odee, D.W. & Dakora, F.D., 2010. African legumes: A vital but under-utilized resource. Journal of Experimental Botany, 61(5), pp.1257-65.
Available at: http://www.ncbi.nlm.nih.gov/pubmed/19939887