Herbal Teas, Infusions and Decoctions: The Art of Plant Preparation

Presentation

Preparing medicinal plants as herbal teas is the most universal and ancient phytotherapeutic practice known to humankind. Every civilization — Egyptian, Greek, Roman, Chinese, Indian, Native American, African — developed sophisticated systems of aqueous plant preparations. The word "tisane" derives from the Greek ptisanê, describing a barley decoction prescribed by Hippocrates as the basis for many remedies. The term encompasses all aqueous plant preparations: infusions, decoctions, and macerations.

Water is the most natural and safest solvent for extracting plant active compounds. Its physicochemical properties — high polarity, hydrogen bonding capacity, variable solvent power with temperature — make it a versatile extractor capable of solubilizing a wide range of compounds: polyphenols, flavonoids, tannins, mucilages, certain alkaloids, mineral salts, water-soluble vitamins, organic acids, and heterosides. However, water does not efficiently extract lipophilic compounds (volatile essential oils, resins, waxes, certain terpenoids), justifying the use of other solvents (ethanol, glycerol) for certain therapeutic applications.

The European Pharmacopoeia regulates the quality of plants for herbal teas. The monograph "Plantae ad ptisanam" defines purity criteria, maximum contaminant levels (pesticides, heavy metals, aflatoxins), storage conditions, and control methods. In France, 148 plants are listed for over-the-counter herbal tea preparation, while pharmacists access an expanded list including plants requiring pharmaceutical advice.

The therapeutic value of herbal teas extends beyond simple active compound extraction. The act of preparing and drinking a tisane has a ritual and psychological dimension — steeping time as a pause, the warmth of the cup, the aromas — that contributes to the overall therapeutic effect, particularly in stress-related functional disorders. Studies on placebo effects and mind-body therapies confirm the importance of this contextual dimension.

Fundamental Principles

The three main aqueous extraction methods differ in water temperature, contact time, and the type of active compounds extracted. An infusion involves pouring simmering water (80–100°C depending on the plant) over plant material, covering, and letting it steep for 5 to 15 minutes before straining. This technique suits fragile plant parts — leaves, flowers, flowering tops — whose active compounds are easily extractable and heat-sensitive. Covering is essential to prevent evaporation of volatile compounds (essential oils) that condense on the lid and return to the preparation.

A decoction involves placing plant material in cold water, bringing to a boil, and maintaining a gentle simmer for 10 to 30 minutes depending on the hardness of the material. This method is reserved for hard, woody parts — roots, bark, stems, seeds, dried fruits — whose thick cell walls require prolonged thermal energy to release active compounds. Decoction extracts more tannins, polysaccharides, and minerals than infusion but may denature some heat-sensitive compounds.

Maceration involves leaving plants in cold or lukewarm water for several hours (4 to 12 hours, even 24 hours) at room temperature. This technique is used for mucilage-rich plants (marshmallow, mallow, flax) whose polysaccharides dissolve slowly in cold water, and for plants whose active compounds are degraded by heat. Cold maceration carries increased microbiological risk and should be consumed promptly.

The plant-to-water ratio is fundamental. The European Pharmacopoeia generally recommends 1 to 2 teaspoons (2–5 g) of dried plant per 200–250 ml of water. This ratio varies with the density of the plant drug: light leaves require more volume than dense roots. Particle size also influences extraction: finely cut plant (tisane cut) offers greater contact surface and faster extraction than coarsely cut material.

Water quality is often overlooked but significantly influences extraction. Low-mineral water (total dissolved solids < 200 mg/L) at a slightly acidic pH (6.5–7.0) optimizes polyphenol extraction. Chlorinated tap water can alter oxidation-sensitive compounds and change taste. Filtered or spring water is preferable.

Technical and Scientific Aspects

From a physicochemical standpoint, aqueous extraction of plant active compounds is governed by diffusion laws (Fick's law) and solubility. The octanol-water partition coefficient (logP) of molecules determines their affinity for the aqueous phase: compounds with negative or low positive logP (< 2) are well extracted by water. Temperature increases solubility of most solid compounds and accelerates diffusion kinetics, but can also cause hydrolysis of certain glycosides and thermal degradation of fragile compounds.

Polyphenols are the compounds best extracted by hot water. Glycosylated flavonoids (rutin, hyperoside, quercetin-3-glucoside) are more water-soluble than their aglycones. Condensed tannins (proanthocyanidins) and hydrolyzable tannins (gallotannins, ellagitannins) are abundantly extracted by decoction, explaining the astringency of tanniniferous herbal teas (tea, red vine, witch hazel). The optimal temperature for green tea catechin extraction is 70–80°C; above this, excessive tannin extraction produces bitterness.

Mucilages are hydrophilic polysaccharides forming viscous solutions on contact with water. Their extraction is maximal in prolonged cold maceration because heat can denature their three-dimensional structure and reduce viscosity. Marshmallow mucilages (Althaea officinalis) consist of arabinogalactans and galacturonans; psyllium mucilages (Plantago ovata) are primarily arabinoxylans.

Essential oils are poorly water-soluble (hydrophobic) but can be partially carried by steam. During a covered infusion, volatile molecules (thymol, carvacrol, menthol, eugenol) condense on the lid and return to the tea. Covering increases volatile compound concentration by 30–60% compared to an uncovered infusion. For aromatic plants (thyme, mint, chamomile), covering during infusion is therefore imperative.

Alkaloids are weak bases whose water solubility depends on pH. In slightly acidic conditions (pH 5–6), they form water-soluble salts. Adding a squeeze of lemon juice (citric acid) to the tea can increase alkaloid extraction and improve bioavailability. Caffeine from tea and coffee, theobromine from cocoa, and berberine from barberry are examples of alkaloids well extracted by hot water.

Mineral salts and trace elements are easily solubilized by water, especially by decoction. Horsetail teas (silicon), nettle teas (iron, calcium, magnesium), and ash teas (potassium) are significant sources of bioavailable minerals. A 30-minute horsetail decoction extracts up to 70% of the plant's soluble silicon.

Steeping time drastically modifies the tisane's composition. For green tea, a 2-minute infusion at 70°C provides primarily L-theanine (relaxing) and catechins; a 5-minute infusion at 100°C releases far more caffeine and tannins (stimulating and astringent). For chamomile, 5 minutes extract anti-inflammatory flavonoids; 15 minutes release deeper sesquiterpenes. This knowledge enables practitioners to tailor preparation to the desired therapeutic effect.

Therapeutic Indications

• Digestive disorders: peppermint infusion (spasmolytic, cholagogue), chamomile infusion (anti-inflammatory, carminative), licorice decoction (antiulcer, demulcent), fennel-anise-caraway infusion (carminative, antispasmodic), lemon balm infusion (spasmolytic, digestive anxiolytic)
• Sleep and anxiety disorders: linden bract infusion (mild sedative, spasmolytic), lemon verbena infusion (calming, digestive), passionflower infusion (anxiolytic, GABAergic), valerian root decoction (sedative — 15 min decoction), orange blossom infusion (sedative, antispasmodic)
• Urinary infections and renal drainage: heather infusion (urinary antiseptic), bearberry infusion (antibacterial arbutin — alkaline urinary pH required), mouse-ear hawkweed infusion (diuretic), cherry stem infusion (aquaretic diuretic), couch grass decoction (diuretic, anti-inflammatory)
• Respiratory conditions: thyme infusion (antiseptic, expectorant), elderflower infusion (sudorific, antiviral), mullein decoction (bronchial emollient), eucalyptus infusion (antiseptic, mucolytic), marshmallow decoction (emollient, mucosal soother)
• Circulatory disorders: red vine leaf infusion (venotonic, antioxidant), witch hazel infusion (venous vasoconstrictor), hawthorn infusion (cardiotonic, mild hypotensive), yarrow decoction (hemostatic, venous tonic)
• Hepatic detoxification and drainage: rosemary infusion (cholagogue, hepatoprotective), dandelion infusion (choleretic, diuretic), burdock decoction (cutaneous and hepatic depurative), artichoke leaf infusion (choleretic, hepatoprotective)
• Metabolic disorders: olive leaf infusion (hypoglycemic, hypotensive), cinnamon infusion (improves insulin sensitivity), gymnema decoction (reduces glucose absorption), green tea infusion (thermogenic, antioxidant)
• Skin conditions (external use): chamomile compresses (anti-inflammatory), thyme foot baths (antifungal), sage gargles (oral antiseptic), cornflower water eye washes (decongestant)

Consultation Process and Prescription

The phytotherapist specializing in herbal teas formulates magistral blends of 3 to 7 synergistic plants. Blend construction follows rigorous methodology, distinguishing the base plant (primary remedy, 30–40% of the blend), complementary plants (synergistic action or addressing associated symptoms, 20–30% each), and corrective plants (taste improvement, gastric protection, 10–15%). Proportions are expressed in equal parts (aa — ana) or weighted parts.

Example formula for spasmodic-dominant irritable bowel syndrome: Mentha piperita folium (peppermint leaf) 30%, Melissa officinalis folium (lemon balm leaf) 25%, Matricaria chamomilla flos (chamomile flower) 25%, Foeniculum vulgare fructus (fennel fruit) 15%, Glycyrrhiza glabra radix (licorice root) 5%. Dosage: 1 tablespoon of blend per 250 ml simmering water, steep 10 minutes covered, strain. 3 cups daily between meals for 3–4 weeks.

The standard dosage for herbal teas is generally 3 to 4 cups daily (750 ml to 1 liter) for adults, distributed throughout the day. Some teas are taken at specific times: digestive teas 30 minutes before or just after meals, sedative teas 30–60 minutes before bedtime, diuretic teas in the morning and early afternoon (to avoid nocturia).

Treatment duration varies by condition: 1–2 weeks for acute disorders (urinary infection, cold), 4–8 weeks for chronic conditions (irritable bowel syndrome, insomnia), with one-week therapeutic windows every 3 weeks for prolonged treatments. Some wellness teas (verbena, linden, rooibos) may be consumed daily without time limitation.

The practitioner trains patients in correct preparation technique: use a stainless steel or glass kettle (avoid aluminum), measure plant quantity precisely, respect temperature and extraction time, always cover, and filter with unbleached paper or stainless steel filters (avoid plastic filters that may release microplastics). Herbal tea should be consumed freshly prepared; it should not be reheated or stored for more than 24 hours (bacterial growth risk).

Administration routes for herbal teas extend beyond oral use. Concentrated decoctions serve as baths (balneotherapy), compresses (dermatology), gargles (ENT), enemas (traditional gastroenterology), inhalations (respiratory medicine), and sitz baths (proctology, gynecology). For compresses, concentration is doubled from oral tisane. For baths, prepare a decoction of 500 g of plant per 5 liters of water.

Traditional Formulas and Variations

• Four-flower tea (pectoral species): classic French pharmacopoeia formula of mallow, marshmallow, mullein, poppy, cat's foot, violet, coltsfoot. Bronchial emollient and antitussive. Preparation: 1.5 g per 150 ml, infuse 10 min
• Hepatic tea (choleretic species): artichoke leaf, boldo leaf, rosemary leaf, peppermint leaf. Stimulates bile secretion and hepatic detoxification. 5 min decoction for artichoke, then 10 min infusion for other plants
• Traditional carminative blend: fennel fruit, green anise fruit, caraway fruit, coriander fruit in equal parts. Anti-bloating and digestive antispasmodic. Lightly crush fruits before infusing to release essential oils. 10 min covered infusion
• Diuretic tea (urological species): bearberry leaf, heather tops, mouse-ear hawkweed whole plant, cherry stems. Urinary antiseptic and diuretic. 5 min decoction then 10 min infusion
• Compound sedative tea: valerian root, passionflower aerial parts, hawthorn flowering tops, lemon balm leaf. Anxiolytic and sleep-inducing. 15 min decoction for valerian, then add other plants for 10 min infusion
• Spring depurative tea: dandelion root and leaf, burdock root, nettle leaf, heartsease. Hepatic, renal, and cutaneous drainage. 10 min decoction for roots, 10 min infusion for leaves
• Remineralizing decoction: horsetail stem, nettle leaf, alfalfa leaf, bamboo exudate. Silicon, calcium, magnesium, and iron supply. 20–30 min decoction for horsetail, 10 min infusion for others
• Galactagogue infusion: fennel fruit, fenugreek seed, green anise fruit, goat's rue aerial parts. Stimulates lactation in breastfeeding mothers. 10 min infusion, 3 cups daily

Contraindications and Precautions

• Plant allergies: Asteraceae (chamomile, echinacea, arnica) are the most common plant allergens. Cross-allergy risk between plants in the same botanical family. Always verify allergy history before prescribing
• Drug interactions: St. John's wort teas reduce efficacy of oral contraceptives, anticoagulants, and immunosuppressants. Daily licorice tea can cause hypokalemia and hypertension in patients on diuretics or antihypertensives. Grapefruit tea inhibits CYP3A4
• Pregnancy: many plants are contraindicated during pregnancy: sage, mugwort, wormwood (uterotonic), senna, buckthorn, cascara (stimulant laxatives, potentially teratogenic), meadowsweet (salicylates). Permitted teas include ginger (nausea), linden (nervousness), lemon balm (digestion)
• Breastfeeding: some plants pass into breast milk and may affect the infant. Large quantities of peppermint can reduce lactation. Sage is galactofuge (anti-lactation). Moderate fennel is compatible
• Renal insufficiency: strongly diuretic teas (hawkweed, cherry stems, couch grass) are inadvisable in severe renal insufficiency. Horsetail is contraindicated in cardiac or renal edema
• Hepatic disorders: choleretic and cholagogue teas (artichoke, boldo, rosemary) are contraindicated in biliary obstruction (symptomatic gallstones, cholangitis). Germander and greater celandine are hepatotoxic with prolonged tea use
• Children under 6: reduced dosages (quarter to half adult dose), menthol-containing plants contraindicated (peppermint, eucalyptus) due to laryngospasm risk. Prefer chamomile, linden, verbena
• Quality and contamination: verify certified organic or wild-harvested origin, absence of pesticides, aflatoxins (damp storage), and heavy metals. Prefer pharmacy or certified herbalist plants over mass-market sources with often insufficient traceability