© Eckard Wolff-Postler · CC BY-SA 3.0 · Commons
Black Spanish radish
CautionSchwarzer Rettich · (Raphanus sativus var. niger)
Cabbage family (Brassicaceae)
Description
Black radish is a winter form of the garden radish: rough, matt-black skin outside, firm and snow-white within, and markedly sharper than a summer radish. It is lifted in autumn and, stored cool and damp, keeps into spring, which long made it an important winter vegetable. Its pungency comes from glucosinolates that break down into isothiocyanates as soon as the root is grated or cut. That is precisely what its medicinal use rests on: the German Commission E recognises fresh radish, or its juice, for digestive complaints originating in the flow of bile — the bitter and pungent compounds stimulate saliva, gastric juice and bile flow and get a sluggish digestion moving. An old household remedy is radish juice with honey for cough, drawn overnight from a hollowed-out root. Care is needed with a sensitive stomach: it is unsuitable in gastritis, peptic ulcer, reflux or acute biliary colic.
Fresh black radish (juice or grated root) is approved by the German Kommission E as a cholagogue for dyspeptic complaints of biliary origin. The isothiocyanates released from glucosinolate breakdown — primarily glucoraphenin and glucoraphasatin — stimulate bile production and secretion. Supports liver detoxification.
Preparation & dosage
Fresh radish juice: 30–40 ml undiluted juice before meals (3 times daily). Alternatively: 50–100 g freshly grated radish root daily. Kommission E daily dose is 50 ml fresh juice divided into 3 doses.
- Doses per day
- 3×
For bloating and sluggish digestion, Kommission E recommends black radish as a bitter-containing digestive. The pungent mustard oil glycosides stimulate gastric gland secretion and intestinal motility. Traditionally also known as a stomach cleanser and liver tonic.
Preparation & dosage
50–100 g freshly grated radish root or 30–40 ml fresh juice with main meals.
- Doses per day
- 3×
Traditionally, black radish juice mixed with honey was used as a cough remedy and expectorant. A tea from dried radish slices is less common but acts mildly as an expectorant through mustard oils and saponins.
Preparation & dosage
Simmer 5–10 g dried radish slices in 200 ml water for 10 minutes, strain. Alternatively: 1–2 tablespoons fresh radish juice with honey 3 times daily.
- Dry amount
- 5–10 g
- Doses per day
- 3×
Laboratory studies show that aqueous black radish extract upregulates cytochrome P450 enzymes (CYP1A1) and phase-II detoxification enzymes (GST) in human liver cells (HepG2). This supports elimination of mutagens and carcinogens. In an animal study, radish diet accelerated excretion of the carcinogen DMBA.
Preparation & dosage
30–50 ml fresh radish juice daily, on an empty stomach. Or 50–100 g freshly grated root with meals.
- Doses per day
- 1×
In Central and Eastern European folk medicine, grated black radish dressed with vinegar and oil is served as a side dish with heavy meals to stimulate digestion and counteract fat overload. The isothiocyanates stimulate bile flow and pancreatic enzymes.
Preparation & dosage
Season freshly grated black radish root with olive oil, apple cider vinegar, and salt. Serve as a salad or side dish.
- Doses per day
- 1×
Alcoholic fresh extract of black radish (1:5, 45 % ethanol) preserves volatile isothiocyanates better than dry extracts. Traditionally used for bile regulation and liver stimulation.
Preparation & dosage
40–50 drops of 1:5 tincture (40–45 % ethanol) before meals, 3 times daily. Do not use with gallstones without medical consultation.
- Doses per day
- 3×
Fresh black radish juice was used in folk medicine topically for fungal skin infections and internally as a general tonic and immune stimulant. Raphanin (isothiocyanate) shows antimicrobial activity against various bacteria and fungi in vitro.
Preparation & dosage
Apply fresh pressed juice topically to affected skin areas or drink 20–30 ml fresh juice daily.
- Doses per day
- 1×
Black radish may cause gastric mucosa irritation and heartburn in sensitive individuals. Do not use with pre-existing gastric ulcers, gastritis, reflux disease, or acute biliary colic. Thyroid disorders: isothiocyanates (glucosinolate breakdown products) may burden the thyroid in high doses (goitrogenic effect) — seek medical advice with existing thyroid conditions. Gallstones: radish stimulates gallbladder contraction, which may trigger colic-like pain in the presence of gallstones.
Safe as food in usual culinary amounts. Medicinal doses (juice therapy) should be avoided during pregnancy as a precaution — no safety studies for therapeutic dosing exist.
Safe as food. Pungent flavour compounds (isothiocyanates) may pass into breast milk and cause colic in the infant. Avoid large quantities.
Safe as food (small amounts) for children over 4 years. Medicinal juice cures not recommended for children under 12 — no dosing data available.
Drug interactions
Levothyroxin / Schilddrüsenpräparate
Isothiocyanates from glucosinolates may influence thyroid hormone synthesis and reduce the efficacy of thyroid medications.
CYP1A1-substrat Arzneimittel
Black radish extract induces CYP1A1 in liver cells; possible influence on the metabolism of CYP1A1 substrates (e.g. theophylline, some oncology drugs).
Contraindications
- Acute biliary colic or bile duct obstruction
- Gastric or duodenal ulcers, acute gastritis
- Hypothyroidism — goitrogenic effect of isothiocyanates
Harvested part: root (autumn-winter)
- Time of day:
- No time-of-day restriction; harvest after the first light frost for more intense flavour
- Drying:
- Use fresh for medicinal purposes (fresh juice) or slice thinly and dry at 40–50 °C. Store dried slices whole or ground.
- Storage:
- 3 months — Fresh root: cool (4–8 °C), dark, high humidity — stores up to 3 months. Dried: airtight, dark, up to 12 months.
- Time of day:
- Harvest in the morning or late morning in dry weather when the seed pods are yellow-brown and dry
- Drying:
- Allow seed pods to finish drying, then thresh and store seeds in paper bags or dark glass jars in a dry location.
- Storage:
- 36 months — Dry, cool, protected from light. Test germination capacity before sowing.
- GlucorapheninGlycosideContent: 0,3–1,5 %Root
Most abundant glucosinolate in black radish; precursor of raphanin (sulphoraphene); shows cholagogue and phase-II enzyme-inducing activity.
- GlucoraphasatinGlycosideRoot
Second most abundant glucosinolate; breakdown product is a potent isothiocyanate; antioxidant and antimicrobial.
- Raphanin (Isothiocyanate-Gemisch)OtherRoot
Enzymatic breakdown product of glucosinolates by myrosinase; active antimicrobial component; responsible for the pungent-bitter taste of radish.
- MyrosinaseOtherRoot
Plant enzyme (thioglucosidase) that cleaves glucosinolates into reactive isothiocyanates. Activated upon maceration or chewing.
- AnthocyaneFlavonoidRoot
Responsible for the dark colour of the black skin and red flesh of some radish varieties; antioxidant. Primarily pelargonidin derivatives.
- Vitamin C (Ascorbinsäure)VitaminContent: 20–30 mg/100 g FrischgewichtRoot
Black radish is a good source of vitamin C; ascorbic acid acts as an antioxidant and supports iron absorption.
- Folat (Folsäure)VitaminRoot
Contains relevant amounts of folate; important for cell division and DNA synthesis.
- KaliumMineralRoot
High potassium content contributes to cardiovascular function and a mild diuretic effect.
- [1]MonographFechner et al. (2011): Screening, Identification and Quantification of Glucosinolates in Black Radish (Raphanus sativus L. niger) Based Dietary Supplements using LC-PDA-LC-MS. J Chromatogr A 1218(39):7033–7039(accessed: 2026-05-24)
- [2]MonographBranka et al. (2014): Raphanus sativus L. var niger as a Source of Phytochemicals for the Prevention of Cholesterol Gallstones. Phytother Res 28(2):288–293(accessed: 2026-05-24)
- [3]MonographHanlon et al. (2007): Aqueous Extract from Spanish Black Radish (Raphanus sativus L. Var. niger) Induces Detoxification Enzymes in the HepG2 Human Hepatoma Cell Line. J Agric Food Chem 55(16):6439–6446(accessed: 2026-05-24)
- [4]MonographHerr et al. (2012): Spanish Black Radish (Raphanus sativus L. Var. niger) Diet Enhances Clearance of DMBA and Diminishes Toxic Effects on Bone Marrow Progenitor Cells. Nutr Cancer 64(8):1287–1296(accessed: 2026-05-24)
- [5]MonographShim et al. (2007): Antioxidant and Choleretic Properties of Raphanus sativus L. Sprout (Kaiware Daikon) Extract. J Agric Food Chem 54(22):8292–8299(accessed: 2026-05-24)
- [7]BookPlants For A Future (PFAF): Raphanus sativus — Radish(accessed: 2026-05-24)
- [6]WikipediaWikipedia EN: Black radish(accessed: 2026-05-24)
🤝 Permaculture Partners
In your garden, this plant acts as:
✨ Best symbiotic partners
Source: Helga und Margarete Langerhorst, Mein gesunder Naturgarten (eigene Kuration)