Rooibos Ferments in the Open, and Processors Heat It Before It Ships

Cederberg processors run rooibos through heat and steam before it ships. The leaf is cut, bruised, and piled into low mounds on open drying yards, watered and turned through the night, what growers have long called fermentation, then spread to dry in the open Cederberg sun. Nothing in that sequence happens inside a sealed vessel.

Why the heat step exists at all

A 2014 peer-reviewed review led by a Stellenbosch University food scientist states: "Rooibos tea, like other plant products, naturally contains a high microbial load." Klipopmekaar, one of the Cederberg's processors, describes the step in its own account of the process: after grading and sieving, rooibos passes through heat and steam treatment "to eradicate any possible organisms which may naturally be found in the growing environment." The step reduces microbes, yeasts, and moulds to levels a food-safety standard will accept. The food-safety standards those facilities must meet include testing for Salmonella, E. coli and other microbes, and the facilities must hold FSSC22000 and ISO 9001 certification.

The pathogen the review calls poorly understood

The same 2014 review says "the presence of Salmonella in Rooibos is poorly understood." The authors write that "gentle processing techniques are necessary for the production of good quality tea," and that this gentleness "has a major influence on the microbiological status of the product." The processing of rooibos, they wrote, "needs to be re-evaluated," with alternative methods that "show great potential to control Salmonella in a fast, efficient and cost-effective manner."

In February 2013, Canada's food inspection agency issued a health hazard alert for Tega brand Organic Lemon Hibiscus Green Rooibos Herbal Tea, made by Nu-Tea Company of Abbotsford, British Columbia, warning that the product might carry Salmonella. The company pulled the affected lots voluntarily. The alert placed the products in the two lower tiers of Canada's three-tier recall system, and no illnesses had been reported.

What brewing does to Salmonella

A 2022 study in Frontiers in Microbiology tested how well Salmonella survives in dried tea, and how reliably brewing kills it. The bacteria can be stubborn in storage: sealed in dry tea at refrigerator temperature, about 4°C (39°F), culturable Salmonella was still detectable after 120 days, and even at room temperature, about 25°C (77°F), a smaller but real count survived that long.

The researchers found that 100°C (212°F) for ten minutes gave more than an eight-log reduction in Salmonella, which in plain terms means it destroyed well over 99.999999 percent of the bacteria present. At 75°C (167°F), some bacteria survived in a dormant, viable state. The authors note that brewing at 100°C, as tested, is unlikely to be a common home-brewing operation. That particular study used black, green, peppermint, and chamomile tea, not rooibos specifically.

Sources

1. Gouws, P., Hartel, T., van Wyk, R., "The influence of processing on the microbial risk associated with Rooibos (Aspalathus linearis) tea,"¹ Journal of the Science of Food and Agriculture 94(15):3069-3078 (2014), on rooibos's natural microbial load, the gentle-processing trade-off, and the call to re-evaluate processing against Salmonella.
2. Rooibos Tea Processing², Klipopmekaar, on the heat/steam sterilisation step, its stated purpose, the testing standards, and FSSC22000/ISO 9001 certification.
3. Health Hazard Alert: Certain TEGA brand Organic Lemon Hibiscus Green Rooibos Herbal Tea may contain Salmonella bacteria³, Government of Canada (23 February 2013), on the Nu-Tea Company recall, its scope, and its outcome.
4. Shi, A., Li, S., Ma, H., Du, X.J., Wang, S., Lu, X., "Survival of Salmonella in Tea Under Different Storage Conditions and Brewing Methods,"⁴ Frontiers in Microbiology 13:816667 (2022), on Salmonella survival in stored dry tea and its inactivation by brewing temperature and time.
5. Rooibos Production and Processing⁵, Carmién Tea International, on the harvest-to-pasteurisation sequence already sourced in The Night Shift Behind Your Calm Cup.