Storing Herbal Tea: Shelf Life, Moisture and Mold
What studies of dry tea found about mold, bacteria and humidity, what they did not test, and why we found no official shelf-life rule for herbal tea.
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Dry herbal tea feels shelf-stable, but dry plant material can still carry mold and bacteria, and damp storage can let them grow. This page describes what studies of dry tea found. It is information, not a storage rule, and we found no official "how long does it last" figure for herbal tea in the sources we could read. Proper evidence not found for a general shelf life, after searching PubMed and agency pages for herbal tea storage, expiration and shelf life.
What the studies found
| Study | What it found | Limits |
|---|---|---|
| Italy, 32 black and green tea products (laboratory survey, 2018) | The authors wrote that improper herbal tea storage (long periods, humid environments) is a health hazard because bacteria and molds can grow. [1] Ochratoxin A, a mold toxin, was detected in 22 of 32 tea solid samples. [1] | Samples were black and green tea (Camellia sinensis), not herbal tisanes; storage conditions were not tested |
| Latvia, 140 Camellia sinensis and 26 herbal teas (2020) | 87% of the tea samples tested positive for 32 fungal species. [2] The authors' exposure estimate, assuming full transfer into the drink, indicated that the analysed teas are safe for consumers. [2] | Herbal and true teas were reported together; one market |
| Lisbon, 40 teas including 10 herbal infusions or white tea (2023) | In the raw tea group, 23 samples (57.5%) had one to five mycotoxins in the same sample. [3] | Mostly green and black tea; results for the herbal infusions were not reported separately in the abstract |
Two points stand out. Mold and mold toxins were common in surveys of dry tea, and the authors of the Latvian study judged the exposure from those samples to be within safe limits on their assumptions. Both can be true, because the surveys describe tea as sold, not tea stored badly for months.
Humidity and warmth in laboratory tests
- A review of mycotoxins in tea says mold toxin production is induced by factors including poor processing methods and environmental factors such as high temperature and humidity. [4]
- In a laboratory test of dried plantain leaf (Plantago lanceolata), leaves held at 75% relative humidity for 24 weeks had intensive microbial growth. [5] Changes at 45% or 0% relative humidity were typically insignificant. [5]
- In a test on Ilex asprella root, a raw material for a Chinese herbal tea, the mold Aspergillus versicolor grew quickly and made large amounts of the toxin sterigmatocystin at humidity of 85% to 90% and temperatures above 26 °C. [6] The herb had been inoculated with the mold and stored for seven days. [6]
These are laboratory conditions with specific plants. They do not tell us how a kitchen cupboard compares, and they do not transfer directly to other herbs.
What a reader can safely do
- Read the label and any date printed on the pack; we did not find an official rule that replaces it.
- If a batch looks or smells wrong, ask the maker or a pharmacist. We found no source that explains how to judge a doubtful batch by eye or smell.
- Keep in mind that mold toxins and bacteria are not the only quality issue; see herbal tea quality and labels and product quality and contamination.
- If you feel unwell after a drink, seek medical care; in the US, Poison Help is 1-800-222-1222.
Not covered
We did not read sources on bagged versus loose storage, freezer storage, or how aroma or strength fades over time. See loose leaf vs tea bags for what sources say about those forms.
Frequently asked questions
How long does herbal tea last?
Proper evidence not found for a general rule. We found studies of mold and bacteria in dry tea but no official shelf-life statement for herbal tea in the sources we read.
Can herbal tea grow mold?
In laboratory tests, dried herbs held in humid conditions showed mold growth, for example dried plantain leaf at 75% relative humidity over 24 weeks. [5]
Is it dangerous to drink tea from a package that was open for a long time?
Not described in the sources we read. The Italian authors wrote that long, humid storage is a hazard because bacteria and molds can grow. [1]
Does the heat of brewing remove mold toxins?
Not described in the sources we read. The Latvian study assumed full transfer of toxins into the drink when estimating exposure. [2]
Where can I read more about contamination?
References
- Cariddi LN et al. Comparative assessment of the quality of commercial black and green tea using microbiology analyses. BMC Microbiology, 2018. Read 2026-10-23.
- Reinholds I et al. Determination of Fungi and Multi-Class Mycotoxins in Camelia Sinensis and Herbal Teas and Dietary Exposure Assessment. Toxins, 2020. Read 2026-10-23.
- Tea contamination by mycotoxins and azole-resistant mycobiota: the need of a One Health approach. International Journal of Food Microbiology, 2023. Read 2026-10-23.
- Mycotoxins along the tea supply chain: A dark side of an ancient and high valued aromatic beverage. Critical Reviews in Food Science and Nutrition, 2023. Read 2026-10-23.
- Effect of high relative humidity on dried Plantago lanceolata L. leaves during long-term storage. Phytochemical Analysis, 2012. Read 2026-10-23.
- Optimization of Storage Conditions of the Medicinal Herb Ilex asprella against the Sterigmatocystin Producer Aspergillus versicolor. Toxins, 2019. Read 2026-10-23.