How to brew herbal infusions safely and well, including the herbs that need cold water

Key takeaways

• Europe’s official monograph on marshmallow root calls for a soak, called a macerate, rather than a boiled brew, and says to use it right after you make it¹³.
• European pharmacy practice uses three methods: cold soaks for slimy roots, 5- to 15-minute hot infusions for delicate parts such as leaves and flowers, and 15- to 30-minute boils for roots and bark³⁵⁶.
• Common European herbal tea monographs call for about 1.5 to 4.5 grams of dried herb per cup, so it pays to weigh what your scoop or tea bag holds⁴⁵⁶.
• Nettle leaf is rich in minerals, but in a small 2024 Serbian study only about 1% to 3% of its iron moved into the tea⁹¹⁵.
• University extension guides advise brewing tea with 195°F water for 3 to 5 minutes, and warn that a sun tea jar won’t get much above 130°F, too cool to kill bacteria⁸¹³.

The official European instructions for marshmallow root tea read more like a kitchen recipe than a drug label. The European Medicines Agency’s monograph, adopted in 2016, calls for chopped root soaked in 150 milliliters of water, used as soon as it’s made¹.

A 2000 reference book on German herbal monographs, cited in the agency’s assessment report, is more specific: 2 to 5 grams of root in cold water for 30 minutes, stirring often, then strain it and warm it before drinking².

Cold water, for a root. Most of us would boil it.

There’s a reason the method matters. Marshmallow root is about a quarter to a third starch, and 5% to nearly 12% mucilage, the slippery material traditionally used to soothe a scratchy throat². European pharmacy practice turns to cold soaks for mucilage-rich plants like this one³.

That one root shows why making herbal tea is a skill. The water, the heat, the time and the amount of herb all change what you drink. So does what happens to the batch after you pour it. This guide covers all of it.

Three ways to get a plant into water

A 2024 paper in the Ukrainian journal News of Pharmacy compared Ukrainian and European rules for water-based herbal preparations, including European pharmacopeia standards and the European Medicines Agency’s guidance³. It lays out three methods.

• Maceration (cold soak). The plant sits in room-temperature water for about 30 minutes. It’s used for mucilage-rich plants³, such as marshmallow root¹.
• Infusion (steep). Water at 90 to 100°C (194 to 212°F) is poured over the plant, which stands for 5 to 15 minutes. It’s used for the plant’s delicate parts³, and Europe’s monographs apply it to leaves and flower blends⁵⁶.
• Decoction (simmer). The plant is boiled for 15 to 30 minutes and strained right away. It’s used for tougher parts: roots, rhizomes (underground stems) and bark³.

These methods are old, yet they have been surprisingly hard to standardize. In 2008, the European Medicines Agency launched an effort to write one EU-wide guideline for preparing herbal teas. It later marked the project discontinued⁷.

Its monographs now point readers to a separate glossary of tea terms instead¹⁵⁶.

In other words, even regulators leave much of the craft to the person holding the kettle.

Heat and time change the cup, but not always the way you’d guess

Some official instructions are precise. Europe’s monograph on sweet fennel fruit, revised in January 2024, calls for 1.5 grams of fruit in 250 milliliters of boiling water, steeped for 15 minutes, three times a day for adults⁴.

Others give an amount and a method but leave the clock to you. The lemon balm monograph simply says 1.5 to 4.5 grams in 150 milliliters of boiling water⁵.

Longer steeping doesn’t make every part of a tea stronger. Polish researchers tested 10 herbal tea products whose makers recommended brewing 5 to 15 minutes¹⁰. Going from 5 to 10 minutes made no significant difference overall in the share of trace minerals that reached the water. For copper, manganese and lead, the longer steep yielded less, while iron, zinc and cadmium went the other way¹⁰.

What about covering the cup? Many herbalists cover a steeping tea to keep aromatic oils from drifting off with the steam. It’s a reasonable, harmless habit, but we found no published measurement of how much it changes a home cup. Treat it as good practice, not proven science.

How much herb makes a medicinal-strength cup

A tea’s strength depends most on how much plant goes in. European monographs, which set doses for registered herbal teas, give these amounts for adults:

Herb or blend	Amount per serving	Water	How often
Lemon balm leaf	1.5 to 4.5 g	150 ml boiling	1 to 3 times a day5
Cough-tea blends (“Species pectorales”)	1.5 to 2 g	150 ml boiling	3 times a day6
Sweet fennel fruit	1.5 g	250 ml boiling, 15 minutes	3 times a day4
Marshmallow root, for throat irritation	0.5 to 3 g	150 ml, soaked	Several times a day, up to 15 g daily1
Marshmallow root, for mild stomach upset	2 to 5 g	150 ml, soaked	3 times a day, up to 15 g daily1

Two lessons hide in that table. First, a “cup” in these monographs is about 5 ounces, smaller than most mugs. Second, the grams matter more than the scoop. A kitchen scale that reads tenths of a gram is the most useful tool an herbal tea maker can own.

Blends deserve a note too. Europe’s monograph on cough-tea blends, adopted in July 2025, recommends no more than four active herbs in one mix⁶. Simple blends make it easier to know what you’re drinking and to spot what disagrees with you.

Nettle “nourishing infusions”: what the mineral numbers show

Some herbalists recommend strong, long-steeped nettle tea as a daily mineral source. The leaf itself is impressive. Researchers at Virginia State University found it rich in calcium, with levels that shifted sharply with the season it was picked¹⁵.

But a leaf’s minerals only count if they reach your cup. The real question is how much leaves the leaf.

For iron, a small 2024 conference paper on nettle from five Serbian sites found only 1.1% to 2.8% moved into a 10-minute infusion⁹. Copper did better, with roughly a quarter to two-thirds extracted⁹. We found no solid measurement of how much calcium reaches the cup.

If minerals are your goal, eat the greens. In that 2013 Virginia State study, published in the International Journal of Food Science, cooked nettle leaves held 376 to 430 milligrams of calcium per 100 grams, and cooking tames the sting¹⁵.

Claim about nettle tea	What research shows	Rating
A good source of iron	In one small study, only about 1% to 3% of the leaf’s iron reached the infusion9	Evidence says no
A good source of calcium	Rich leaf, but no reliable data on how much dissolves15	Not enough evidence
Steeping longer pulls out more minerals	In one study of 10 herbal teas, an extra 5 minutes made no significant overall difference10	Not enough evidence

Herbal tea becomes a perishable drink once it’s brewed

Dried leaves are a farm product, and they can carry bacteria. In 1996, the CDC sent state health officials a memo about bacteria in iced tea, later summarized by Food Safety News¹¹. It said tea leaves may carry coliform bacteria, most often Klebsiella and Enterobacter, which can grow when tea is brewed too cool, held too long or kept in a dirty urn¹¹.

The CDC’s advice to restaurants was to brew at 195°F for 3 to 5 minutes, store iced tea no longer than 8 hours and clean the brewer, dispenser and spigot every day¹¹. It also said it knew of no outbreaks clearly tied to tea¹¹. The risk is low, and good habits keep it that way.

The memo was about restaurant iced tea, but the same logic fits any leaf brewed in water. Fecal coliform bacteria turned up in U.S. restaurant iced tea in 1995. A 1997 study in the Journal of Food Protection concluded they got in after steeping, through poor sanitation¹².

University extension services give similar home advice. Illinois Extension says to heat water to 195°F, steep 3 to 5 minutes, refrigerate after brewing, and never leave brewed tea at room temperature more than 8 hours⁸.

Sun tea skips the heat. The CDC memo called sun-brewed tea a higher theoretical risk¹¹. Ohio State University Extension notes that a sun tea jar won’t get hotter than about 130°F, which isn’t hot enough to kill bacteria¹³.

Ohio State suggests steeping tea in cold water in the refrigerator instead, and brewing only what you’ll drink within a few hours¹³. Tea that turns thick or syrupy may be growing a ropy bacterium¹³.

Cold soaks skip it too. Europe’s marshmallow monograph says to use the soak right away, and the older method warms it before drinking¹².

Your fridge may be warmer than you think. A 2011 food-safety review cited a 1999 survey of 939 U.S. home refrigerators in which 27.4% ran warmer than 41°F (5°C)¹⁴. A cheap fridge thermometer settles the question.

The tool: an infusion method card

Use this card to match the method to the plant part. Amounts are for one adult serving from the European monographs; when a product label gives directions, follow the label.

Herb type	Method	Amount	Time	After brewing
Leaves and flowers (lemon balm, cough blends)	Infusion, just-boiled water	1.5 to 4.5 g per 150 ml56	5 to 15 minutes3	Drink fresh; chill leftovers
Seeds and fruits (fennel)	Infusion, boiling water	1.5 g per 250 ml4	15 minutes4	Drink fresh
Mucilage-rich roots (marshmallow)	Cold soak	0.5 to 5 g per 150 ml1	About 30 minutes, stirring2	Use right away1
Roots, rhizomes and bark	Decoction, simmer	Per product or monograph	15 to 30 minutes3	Strain at once; chill leftovers
Batch for iced tea	Brew hot, then chill	Per recipe	3 to 5 minutes at 195°F for tea8	Refrigerate; no more than 8 hours at room temperature8

Pregnancy, children and the blends to read closely

European monographs often say an herb is “not recommended” in pregnancy. Read that carefully. Usually it means safety hasn’t been studied, not that harm has been shown. Europe applies that wording to lemon balm, marshmallow root and most cough-tea blends¹⁵⁶.

A few herbs carry more specific cautions:

• Fennel. Europe’s 2024 monograph advises against fennel tea in pregnancy and breastfeeding. It points to laboratory and animal data on estragole, a natural compound in fennel, and notes that another fennel compound, trans-anethole, passes into breast milk⁴. It also advises against fennel tea for children under 4⁴.
• Willow bark in blends. The 2025 cough-tea monograph says blends with willow bark are not recommended in the first two trimesters and should not be used in the third. They’re also ruled out for anyone under 18, since willow bark carries a Reye’s syndrome risk for young people⁶.
• Meadowsweet and licorice in blends. The same monograph says blends containing them aren’t recommended for anyone under 18⁶.
• Marshmallow root. Not for children under 3 for throat use, or under 12 for stomach use. Space it half an hour to an hour away from other medicines, because it may slow their absorption¹.

Our guide to judging herbal teas covers licorice and blood pressure, St. John’s wort interactions and plant toxins called pyrrolizidine alkaloids. If you’re pregnant, nursing or brewing for a child, bring your tea list to your clinician, since most monographs lack safety data for those groups¹⁴⁶.

Tea-making is a household skill worth keeping

Brewing herbs is one of the most personal ways to care for yourself and your family. It asks for patience, attention and a few good tools, and it rewards you with a ritual you control from plant to cup.

Respecting that skill means treating it like cooking. Weigh your herbs, match the method to the plant, keep your jars clean and your fridge cold. The tradition is strongest when it’s practiced carefully.

When to get help

See a clinician if a sore throat or cough lasts more than a week, or comes with fever, trouble breathing or pus-filled mucus, whatever you’re drinking for it¹. Stop a tea and get advice if symptoms get worse while you use it⁴.

For a stomach complaint, Europe’s marshmallow monograph says to see a clinician if it lasts beyond two weeks¹. Its fennel monograph caps fennel tea at two weeks for adults and under one week for children 4 to 12⁴. A remedy that needs longer deserves a proper diagnosis.

Questions readers ask

The bottom line

Good herbal tea starts with matching the method to the plant: cold soaks for slippery roots, hot steeps for leaves and flowers, and simmering for roots and bark. Weigh your herbs, because the grams decide the strength.

Then treat the result like food. Brew hot unless the plant calls for a soak, keep batches small and cold, skip sun tea, and check pregnancy and children’s cautions for every herb in the blend.

Related reading

• Water, alcohol or oil: how an herb’s form changes what you get
• How to judge a cup of herbal tea, which is gentle but not automatically harmless
• Chamomile nudged sleep quality in small trials without fixing insomnia
• Date labels mostly track quality, while a fridge thermometer tracks safety
• Herbal supplements are a $13 billion business, and herbalists need no license

Sources

1. European Medicines Agency, Committee on Herbal Medicinal Products. “European Union Herbal Monograph on Althaea officinalis L., radix.” EMA/HMPC/436679/2015, adopted July 12, 2016. ema.europa.eu
2. European Medicines Agency, Committee on Herbal Medicinal Products. “Assessment Report on Althaea officinalis L., radix” (draft revision). EMA/HMPC/436680/2015, November 24, 2015. ema.europa.eu
3. Fedorovska MI, Sinichenko AV, Polovko NP. “A Comparative Analysis of Compounding Aqueous Extracts From the Medicinal Plant Raw Material in Accordance With the Requirements of the Regulatory Legal Acts of Ukraine and the European Union.” News of Pharmacy, 2024;107(1):13–21. nphj.nuph.edu.ua
4. European Medicines Agency, Committee on Herbal Medicinal Products. “European Union Herbal Monograph on Foeniculum vulgare Miller subsp. vulgare var. dulce, fructus, Revision 1.” EMEA/HMPC/372839/2016 Rev. 1, adopted January 31, 2024. ema.europa.eu
5. European Medicines Agency, Committee on Herbal Medicinal Products. “Community Herbal Monograph on Melissa officinalis L., folium.” EMA/HMPC/196745/2012, May 14, 2013 (copy hosted by e-lactancia.org). e-lactancia.org
6. European Medicines Agency, Committee on Herbal Medicinal Products. “European Union Herbal Monograph on Species pectorales.” EMA/HMPC/239465/2024, adopted July 9, 2025. ema.europa.eu
7. European Medicines Agency. “Development of a Guideline on Preparation of Herbal Teas: Scientific Guideline.” EMA, concept paper published September 4, 2008; status discontinued. ema.europa.eu
8. Smith J. “The Dangers of Sun Tea.” Illinois Extension, University of Illinois, July 5, 2018. extension.illinois.edu
9. Antonijević Nikolić M, Popović K, Đuričić-Milanković J, et al. “Elemental Composition of Infusions of Stinging Nettle Collected From Different Localities in Serbia.” Physical Chemistry 2024 (17th International Conference on Fundamental and Applied Aspects of Physical Chemistry), Proceedings Vol. II, 2024:663–666. doi.ub.kg.ac.rs
10. Sembratowicz I, Rusinek-Prystupa E. “Effects of Brewing Time on the Content of Minerals in Infusions of Medicinal Herbs.” Polish Journal of Environmental Studies, 2014;23(1):177–186. pjoes.com
11. Schreck S. “Did You Know? Iced Tea Safety” (summarizing the CDC’s 1996 memo on bacterial contamination of iced tea). Food Safety News, June 2010. foodsafetynews.com
12. Zhao T, Clavero MRS, Doyle MP, Beuchat LR. “Health Relevance of the Presence of Fecal Coliforms in Iced Tea and Leaf Tea.” Journal of Food Protection, 1997;60(3) (abstract record, International Institute of Refrigeration). iifiir.org
13. Ohio State University Extension. “Is Sun Tea Safe?” Live Smart Ohio, August 19, 2011 (updated May 2023). livesmartohio.osu.edu
14. Nummer BA, Schaffner DW, Fraser AM, Andress EL. “Current Food Safety Issues of Home-prepared Vegetables and Herbs Stored in Oil.” Food Protection Trends, 2011;31(6):336–342. foodprotection.org
15. Rutto LK, Xu Y, Ramirez E, Brandt M. “Mineral Properties and Dietary Value of Raw and Processed Stinging Nettle (Urtica dioica L.).” International Journal of Food Science, 2013:857120. pmc.ncbi.nlm.nih.gov