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

Cederberg processors run rooibos through heat and steam before it ships. That is not a marketing claim. It is standard practice at the plants that handle the leaf, and the reason for it sits in plain sight in our own account of how the leaf is made: 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. It happens on the ground, in the weather, the way it has for a century. That openness is also, honestly, the reason the finished leaf cannot simply be bagged and shipped.

Why the heat step exists at all

Rooibos, like any crop grown and handled outdoors, picks up a naturally high load of ordinary environmental microbes along the way, a fact a 2014 peer-reviewed review by food scientists at Stellenbosch University and the University of the Western Cape states plainly: "Rooibos tea, like other plant products, naturally contains a high microbial load." Almost anything cut in a field and dried in open air, rather than grown under glass, picks up the same kind of load. What is specific to rooibos is what happens next. Klipopmekaar, one of the Cederberg's processors, describes the required step in its own account of the process: after grading and sieving, every batch passes through heat and steam treatment "to eradicate any possible organisms which may naturally be found in the growing environment," reducing microbes, yeasts, and moulds to levels a food-safety standard will actually accept. The Ministry has already set out the mechanics of that step for the everyday batch: leaf heated hot enough that the tea itself reaches about 94°C (201°F), just short of a full boil, and held there for at least 90 seconds, longer if the client's own specification calls for it, the food-safety half of processing that has nothing to do with flavour. Klipopmekaar adds the part that rarely makes it onto a tin: finished batches are also screened directly for Salmonella, E. coli, and other microbes before shipment, at facilities that hold FSSC22000 and ISO 9001 food-safety certification.

The one pathogen the heat step cannot fully promise

Here is the honest complication, and it is worth sitting with rather than smoothing over. The same 2014 review that documents rooibos's natural microbial load goes on to say something a tin of tea will never tell you: "the presence of Salmonella in Rooibos is poorly understood," and the processing the industry actually uses has a built-in limit. Rooibos cannot be blasted with the kind of aggressive, high-heat sterilisation that would reliably flatten every organism, because that same aggression would cook the delicate flavour compounds, and the antioxidant aspalathin that gives green rooibos its point, out of the leaf. The review's own authors put it as a trade-off, not a failure: "gentle processing techniques are necessary for the production of good quality tea," and that gentleness "has a major influence on the microbiological status of the product." Their conclusion reads like a to-do list, not an alarm: the processing of rooibos, they wrote, "needs to be re-evaluated," with gentler alternatives to plain steam pasteurisation holding real promise for controlling Salmonella specifically, "in a fast, efficient and cost-effective manner," without ruining the cup.

This is not a hypothetical worry. 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, not the top tier reserved for the most serious health consequences, and no illnesses were ever reported tied to it. Nobody was hurt. But a real batch of green rooibos blend, sold on a real shelf, genuinely needed pulling, which is exactly the scenario the Stellenbosch review had in mind when it called the industry's reliance on steam alone something to keep improving rather than something already solved.

What actually finishes the job

A cup of rooibos is still a safe bet. The safeguard a reader can trust most for it, though, is not printed on any label, and it is not exotic: it is the kettle. A 2022 study in Frontiers in Microbiology tested how well Salmonella survives in dried tea, and how reliably ordinary 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. Brewing, though, is a different matter entirely once the water is genuinely hot enough. The researchers found that a full boil, 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. The catch is the word "genuinely." At 75°C (167°F), some viable bacteria survived the same treatment, and at 55°C (131°F) and below, the study found brewing could not reliably inactivate Salmonella at all. That particular study used black, green, peppermint, and chamomile tea, not rooibos specifically, but the mechanism it measured, heat overwhelming a bacterium's tolerance, does not care what plant the dried leaf came from. A rooibos leaf brought properly off the boil gets the same physics.

Two safeguards, not one

Put the two halves of this together and the picture is more reassuring than either half alone, though it still asks something of the reader, not just the processor. Before it ever reaches a shop shelf, a batch of rooibos has already been heat-treated once, at the plant, specifically because it fermented and dried in the open, and screened directly for the pathogens that step exists to catch, at facilities certified against a real food-safety standard. That is a genuine, tested safeguard. It is also, by the field's own peer-reviewed admission, an imperfect one for a single organism that the industry is still working to control better, and the gap that leaves is closed by something plainer than any label or marketing claim: the same instruction the Ministry has always given, said here for a different reason than usual. Bring the water to a proper, rolling boil, and keep it there a real minute or two, not just the first bubbles. The Shi study's own strongest number, that eight-log kill, was measured at a full 100°C (212°F) held for ten minutes, and its authors say plainly that a shorter or gentler pour, the kind most kettles actually deliver, may not fully clear Salmonella from a cup. Give the water the time as well as the heat, and the one pathogen a delicate leaf's own processing cannot fully rule out is facing the best odds the evidence actually offers, not a guarantee, but the closest thing to one a kettle can give.

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 and improve pasteurisation against Salmonella specifically.
2. Rooibos Tea Processing², Klipopmekaar, on the heat/steam sterilisation step, its stated purpose, the Salmonella/E. coli screening requirement, 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, corroborating the mechanics of the harvest-to-pasteurisation sequence already sourced in The Night Shift Behind Your Calm Cup.