Borgmann Aquaponics Hydroponics
Infusion & Tea Extract
Herbal tea is the oldest and most widespread form of medicinal plant application worldwide – and at the same time the most underestimated extraction method. "Pour hot water over it" describes the principle, but not the chemistry. The European Pharmacopoeia (Ph. Eur.) distinguishes between three different aqueous preparation forms with fundamentally different physical conditions, active compound profiles, and areas of application. Whoever confuses them will obtain a fundamentally different product from the same plant material – or none at all.
Three Methods – A Necessary Distinction
The Ph. Eur. defines in chapter 4.1.3 three official aqueous preparation forms for medicinal drugs, which are often indiscriminately summarized as "tea" in everyday life. The differences are not academic but practically effective: They determine which classes of active compounds are extracted, whether heat-sensitive substances are preserved, and whether the preparation is ready to drink or ineffective.
Infusum – Infusion
Boiling water is poured over the plant material; the vessel is immediately covered; steeping time 5–15 minutes; then strain. Suitable for: flowers, leaves, delicate herbs, drugs containing essential oils. Covering is mandatory – volatile active compounds (essential oils) would otherwise evaporate with the rising steam.
Decoctum – Decoction
Plant material is started in cold water, then brought to a boil and simmered gently for 10–30 minutes; then allowed to cool and strained. Suitable for: roots, barks, seeds, hard plant parts with dense cell walls. Not suitable for drugs with volatile or thermolabile active compounds.
Maceratum – Cold Macerate
Plant material is placed in cold water (15–20 °C) and extracted for 30 minutes to 12 hours without heat; then strained. Suitable exclusively for mucilage-containing drugs, whose mucilage denatures or is converted into undesirable degradation products when heated. The cold macerate preserves the intact gel structure of the polysaccharides.
In common parlance and in the kitchen, all three are often grouped together as "tea". For therapeutic application, however, choosing the correct method is as important as choosing the correct plant.
Physical-Chemical Principles
Water as a polar solvent – strengths and limitations
Water is the most polar common solvent, with a dipole moment of 1.85 Debye and a Hildebrand solubility parameter of approx. 47 MPa½. It excellently dissolves all hydrophilic (water-soluble) compounds: polysaccharides, mucilages, tannins, glycosides, organic acids, water-soluble vitamins (C, B-complex), mineral salts, and many flavonoids. In contrast, lipophilic substances such as essential oils (aside from small amounts entrained in the steam during infusion), resins, waxes, chlorophyll, and fatty oils are not or only poorly accessed. Aqueous extracts thus have a complementary active compound profile to oil extracts and tinctures – a fact that can be specifically utilized in combination therapy with medicinal plants.
Temperature as an extraction variable – and its double-edged effect
Heat accelerates diffusion and increases the solubility of most compounds in water. However, it also has a destructive effect on a number of valuable classes of active compounds. Resolving this contradiction is the true art of aqueous extraction:
| Active compound class | Optimal extraction temperature | Effect of heat |
|---|---|---|
| Essential oils (volatile terpenoids) | Infusion, covered, 90–95 °C | |
| Flavonoids, phenolic acids | Infusion, 90–95 °C, 10 min | |
| Tannins | Infusion or decoction | |
| Mucilages, polysaccharides | Cold macerate, max. 30 °C | |
| Iridoid glycosides (e.g., harpagoside) | Infusion or short decoction | |
| Enzymes, proteins | Cold macerate or max. 40 °C | |
| Alkaloids (basic) | Slightly acidic infusion or decoction | |
| Saponins | Decoction (15–20 min boiling) |
Why covering during infusion is not a minor detail
When infusing drugs containing essential oils, immediately covering the vessel is not an optional recommendation but a physical necessity. As described in Article 2 of this series on steam distillation, essential oils have a measurable vapor pressure even at temperatures below 100 °C and are continuously carried out of the open vessel by the rising water vapor. With a steeping time of 10 minutes in an open vessel, depending on the plant and temperature, 30–60 % of the volatile terpenes can be lost. The result is an infusion that smells of the plant – because the aromatic substances are in the room air, no longer in the tea. For chamomile, peppermint, thyme, and lemon balm, covering is therefore directly relevant to efficacy.
Water quality – an underestimated factor
Tap water in regions with high water hardness contains dissolved calcium ions (Ca²⁺) and magnesium ions (Mg²⁺), which can form poorly soluble complexes with tannins and inhibit the extraction of certain active compound groups. Especially for tannin-rich drugs (oak bark, blackberry leaves, green tea), the use of soft water or filtered water is recommended. Lime deposits on the tea surface are not a quality defect of the tea but precipitates of insoluble calcium salts – they affect the appearance but only slightly influence the active compound content.
Microbiological stability – why tea spoils quickly
An aqueous plant extract is a microbiologically unstable system. Water as a solvent offers no preserving properties; the plant material inevitably introduces germs, fungal spores, and yeasts. Added to this is a high content of carbohydrates, organic acids, and nutrients that provide optimal growth conditions for microorganisms. At room temperature, an aqueous extract is considered microbiologically questionable within 12–24 hours; in the refrigerator, this period extends to 2–3 days. Therefore, the rule for therapeutically used teas is: prepare fresh daily, never brew in advance. In contrast, tinctures (Article 4) with over 40 % ethanol are stable for 2–5 years – a difference of several orders of magnitude that directly reflects the microbial stability of the solvent.
Plant-Specific Characteristics – which method for which drug
The choice between infusion, decoction, and cold macerate is not a matter of taste but results from the active compound localization, cell structure, and thermal stability of the target compounds. Some examples from the practice textbook:
Chamomile (Matricaria chamomilla) – Infusion
Chamomile flowers contain the essential oil with bisabolol and the blue azulene (chamazulene), which is only formed from its precursor matricin through the heat of the infusion – a thermal conversion step that actually requires a certain amount of heat input. At the same time, the apigenin glycosides as anti-inflammatory flavonoids are highly water-soluble and transfer completely at 90–95 °C. Mandatory: cover and steep for 5–10 minutes. Steeping times that are too long (over 15 minutes) increase the tannin content and create a bitter-astringent character that is therapeutically counterproductive for gastric and intestinal irritation.
Marshmallow root (Althaea officinalis) – Cold macerate mandatory
Marshmallow root is the prime example of a mucilage drug where the method makes the crucial difference. The mucilage (a mixture of arabinogalactans and other heteropolysaccharides) forms a highly viscous, mucilaginous gel in a cold macerate, which mechanically protects the mucous membranes of the mouth, throat, and esophagus and soothes irritation. With hot water (above 60 °C), these polysaccharides partially denature and hydrolyze; the finished product is significantly thinner and less effective than the cold macerate. The recommendation is: 2–4 g of cut root in 150 ml of cold water, stir or let stand for 30–60 minutes, strain, and drink. The finished cold macerate can be warmed to drinking temperature before consumption – this does not harm the gel, as it is already stabilized.
Peppermint leaves (Mentha × piperita) – Infusion, strict covering requirement
Peppermint tea is the most consumed herbal tea in Germany – and is shockingly often prepared incorrectly in households. The essential oil with its main component menthol (30–55 %) is the therapeutically relevant active compound (spasmolytic, carminative, mildly antibacterial). Menthol is volatile and evaporates quickly in an open vessel. Recommended practice: boiling water, cover immediately, steep for exactly 5–8 minutes. Steeping too long increases the tannin content and makes the tea intolerable for people with heartburn and reflux – peppermint relaxes the lower esophageal sphincter and can thus trigger or exacerbate reflux. For infants and young children, peppermint tea is contraindicated due to the menthol content (risk of respiratory distress).
Devil's claw root (Harpagophytum procumbens) – Cold macerate or short decoction
Devil's claw is a good example of the necessity of knowing the Ph. Eur. method precisely. The main active compound harpagoside (an iridoid glycoside) is moderately thermolabile: A short infusion at 90 °C for 10 minutes is acceptable and extracts harpagoside well. However, a cold macerate overnight (8–12 hours in cold water) yields the highest harpagoside yield with the least degradation – and is recommended as the preferred method by the German Commission E as well as ESCOP. Prolonged boiling (decoction), on the other hand, is unfavorable: It demonstrably degrades harpagoside and yields a therapeutically weaker extract, although the result appears visually darker and more intense.
Step-by-Step by Method
Infusion (Infusum)
Decoction (Decoctum)
Cold Macerate (Maceratum)
Safety Instructions & Limits of Self-Medication
Drugs that must not be prepared as tea
The Ph. Eur. and the German Commission E explicitly point out that some medicinal plants must not be marketed or used as tea due to their toxicity. This includes, among others:
- Mistletoe (Viscum album): Lectins and viscotoxins are partially inactivated during boiling – but dangerous as a raw extract; clinical use only as a standardized injectable extract.
- Yew (Taxus baccata): all parts except the red seed coat (arillus) contain highly toxic taxanes; life-threatening as tea.
- Digitalis species: Cardiac glycosides with a narrow therapeutic window; only under medical supervision and as a standardized finished medicinal product.
- Autumn crocus (Colchicum autumnale): Colchicine is present in all parts; confusion with bear's garlic or wild garlic leads to poisoning cases every year.
Interactions with medications
Aqueous plant extracts can interact with medications, even if they are considered "natural" or "harmless". Known clinically relevant examples: St. John's wort tea (and extracts) induces the cytochrome P450 enzyme CYP3A4 and P-glycoprotein, which can significantly reduce the effectiveness of immunosuppressants (cyclosporine), anticoagulants (warfarin), antiretroviral therapy, and oral contraceptives. Grapefruit juice and bitter orange peel inhibit the same enzyme, thus increasing the bioavailability of some drugs to dangerous levels. Anyone who takes medication regularly should seek medical advice before the therapeutic use of herbal teas.
Dosage and therapeutic range
Compared to tinctures or extracts, the active compound content of a tea is difficult to standardize – it depends on the amount of drug, water quality, temperature, steeping time, and the quality of the plant material. The Ph. Eur. explicitly cites this lack of dosage accuracy as a limitation of aqueous preparations. For diseases requiring precise dosing, standardized finished medicinal products are preferable to home-brewed tea for quality reasons.
Conclusion of the Series – The Five Methods Compared
Each extraction method accesses a different spectrum of active compounds. The following overview summarizes the series and helps in selecting the appropriate method.
| Method | Solvent | Accessed active compound classes | Shelf life | Suitability for home use |
|---|---|---|---|---|
| Oil extract (Maceration) | Fatty oil | Lipophilic substances: terpenoids, carotenoids, fat-soluble vitamins | 6–18 months | very good |
| Steam distillation | Water vapor | Exclusively volatile essential oils; hydrolat as by-product | 6 months – 3 years | limited |
| Cold pressing | – | Fatty oils (triglycerides) or volatile citrus oils | 3–24 months | limited |
| Tincture (Alcohol) | Ethanol / water mixture | Broadest spectrum: hydrophilic + lipophilic; concentration controllable | 2–5 years | very good |
| Aqueous extract (Tea) | Water | Hydrophilic substances: glycosides, tannins, mucilages, flavonoids | 12–48 hours | optimal |
Further Specialized Literature
- European Pharmacopoeia (Ph. Eur.), Chapter 4.1.3: Tea preparations (Plantae ad ptisanam). EDQM Strasbourg; continuously updated. — Official definitions for Infusum, Decoctum, and Maceratum; dosage guidelines and quality requirements for tea drugs.
- Blaschek W. (Ed.): Wichtl – Teedrogen und Phytopharmaka. 6th Edition, Wissenschaftliche Verlagsgesellschaft Stuttgart, 2016. ISBN 978-3-8047-3068-7. — Monograph work with plant-specific information on the preparation form (infusion, decoction, cold macerate) and therapeutic dosage recommendations.
- Hänsel R., Sticher O.: Pharmakognosie – Phytopharmazie. 8th Edition, Springer-Verlag Heidelberg, 2007. ISBN 978-3-540-26508-5. — Chapter "Aqueous preparations": Physical-chemical principles of infusion, decoction, and maceration; thermal stability of active compound classes; verified via SpringerLink and AbeBooks.
- Teuscher E., Melzig M.F., Lindequist U.: Biogene Arzneimittel. 7th Edition, Wissenschaftliche Verlagsgesellschaft Stuttgart, 2012. ISBN 978-3-8047-2285-9. — Foundational work on ingredients, pharmacology, and preparation; sections on aqueous extraction methods and microbiological stability; existence confirmed via ciando and DNB.
- Federal Institute for Drugs and Medical Devices (BfArM): Commission E monographs on chamomile flowers, peppermint leaves, marshmallow root, and devil's claw root. — Publicly accessible at bfarm.de; contain information on the preparation form, daily dose, and contraindications for aqueous medicinal drug extracts.
The temperature specifications for active compound stability and the shelf life guidelines are based on generally accepted values from pharmacognosy and food chemistry. For therapeutically used teas, consultation of the Commission E monographs or ESCOP monographs for the respective plant material is recommended.
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