The Same Long Steep That Is Kind to Rooibos Is Not Kind to a Mesh Tea Bag

This office has told readers for years to leave the pot alone. Rooibos carries almost no tannin, so a full boil held ten minutes, twenty, even a forgotten hour, comes back strong rather than bitter, as this Ministry's own brewing guide records. That advice still holds. What it did not account for is that the same near-boiling water, held that same long time, is precisely the condition a run of tea-bag studies have identified as the one that strips the most plastic out of a mesh bag and into the cup. Rooibos's patience with heat and time is not in question. What sits in the water while it waits is.

What a mesh bag is actually made of

The pyramid-shaped bag that looks like silk is rarely silk. Most are woven nylon or PET, food-grade plastic chosen because it is heat-stable and does not colour the water, and in 2019 a McGill University team led by Nathalie Tufenkji tested what that weave does at brewing heat. A single plastic teabag, heated in water to simulate steeping, released about 11.6 billion microplastic particles and 3.1 billion nanoplastic particles, the team reported in Environmental Science & Technology, a figure the university's own announcement called thousands of times higher than anything previously measured in food. That is one bag, once.

A 2024 follow-up from the Universitat Autonoma de Barcelona, working with Germany's Helmholtz Centre for Environmental Research, measured the release more precisely across materials: polypropylene bags shed about 1.2 billion particles per millilitre of tea, nylon-6 about 8.18 million particles per millilitre, the team found. The same study, led by Gooya Banaei, put the released particles in contact with human intestinal cells in the lab and found the mucus-producing cells took up the most of them, some reaching into the cell's own nucleus. That result describes a laboratory dish, not a body, and it does not show the particles crossing into the bloodstream. It is still the first time anyone had shown a teabag's plastic getting inside a human cell at all.

Why the Ministry's own advice makes it worse, not better

Neither of those studies varied the steep. A 2025 study out of Russia's Enikolopov Institute did, testing nylon, polypropylene, and cellulose bags at 20, 50, and 100 degrees Celsius (about 68, 122, and 212°F) over steeps from an hour to several days. The finding was blunt: the concentration of released particles rises with both higher temperature and longer time, the authors reported in the journal Polymers, for every material tested. A full boil is the top of that scale. Ten to twenty minutes, this Ministry's own recommended range, is far past the five-minute steep the earlier studies used to get their numbers. Nothing about rooibos changes the chemistry. It only removes every reason to cut the steep short, which is exactly the one lever that would.

"Plant-based" is not automatically the fix

The tidy answer, switch the mesh for something that sounds natural, does not hold up cleanly either. The 2025 Polymers study tested cellulose bags alongside the plastic ones and found their peak particle concentration during the brew, 170 billion particles per litre at the high end, actually ran higher than the synthetic bags' peak of 14 billion per litre. The consolation is what happens next: over the study's ten-day observation window, the cellulose particles broke down to nothing detectable, while the synthetic ones showed no measurable degradation at all. A cellulose bag sheds hard in the cup you are about to drink and then disappears from the world; a plastic one sheds less in that one cup but the particles persist. Neither is the same thing as harmless.

Rooibos brands selling bagged tea have mostly reached past cellulose, for PLA, a corn-starch bioplastic marketed as compostable and used in place of the woven mesh. BOS Brands, one of South Africa's own rooibos producers, switched its bags to a PLA filter paper specifically to avoid the polypropylene sealing agents common in conventional bags, a real and verifiable step away from the material the McGill and Barcelona studies measured directly. None of the studies this piece could find have tested PLA itself at brewing temperature the way they tested nylon, polypropylene, and cellulose, so what can honestly be said stops there: PLA is chemically distinct from the plastics the research condemns, and no study yet says it is clean.

What changes, and what does not

Nothing here is an argument against rooibos, or against the Ministry's own advice on how to brew it. A general Afrikaans-language consumer piece on the same question, aimed at a South African readership that has been asking about this for longer than the English-language coverage suggests, reaches a similarly unhurried conclusion: manufacturers hold that the plastic in a sealed bag is minimal and within international food-safety limits, and consumer researchers quoted there see no cause for panic. That is a fair summary of where the science actually sits: real, measured, still being worked out, not a reason to stop drinking tea.

What it changes is the format, not the leaf. Loose rooibos in an infuser or a pot puts nothing between the water and the plant, and a plain paper bag without a synthetic seal is the next-safest choice research has actually tested. A mesh pyramid bag left in a mug for twenty minutes at a full boil, the exact treatment this Ministry has spent years recommending, is the one combination the evidence keeps pointing back to. The tea was never the problem. What holds it may be.