Rehmannia Root: From Raw to Cooked, A Healing Herb

Rehmannia root, a cornerstone of Chinese medicine for centuries, is a powerful herb with a remarkable transformation from raw to cooked forms. Known for cooling the body or nourishing it depending on preparation, this plant—often called "earth marrow"—offers a range of health benefits. Let’s dive into its origins, appearance, uses, and how its raw and cooked versions differ, making it easier to understand this herbal gem.

What Is Rehmannia Root?

Rehmannia root, or Rehmannia glutinosa, is a perennial herb from the Scrophulariaceae family. Its medicinal part is the rhizome, a thick underground stem dug up in autumn or early winter, especially in Huaiqing, Henan Province, where the best quality grows. Farmers clean the roots, remove stems and hair-like roots, then dry them slowly over low heat or in the sun to preserve their healing properties.

The plant thrives in sunny spots with loose, fertile sandy soil but struggles with drought or waterlogged conditions. Its nickname, "earth marrow," comes from its ability to soak up the soil’s nutrients, requiring crop rotation to keep the land fertile.

Raw Rehmannia

Appearance of Rehmannia Root

Rehmannia root has a distinct look. Its rhizomes are irregularly shaped, round, and thick, with a soft, sticky texture that’s tough to break. Fresh roots are bright yellow, giving the herb its Chinese name, "di huang" (yellow earth).

After drying, raw rehmannia turns brown-black or grayish-brown, with a glossy, sticky surface. Cooked rehmannia, steamed and processed further, becomes darker and sweeter, with a softer, more pliable texture.

Rehmannia Root

Benefits of Raw Rehmannia Root

Raw rehmannia is cool in nature, sweet in taste, and works on the heart, liver, and kidneys. It’s excellent for:

• Cooling the Body: It clears heat and cools blood, helping with high fevers, rashes, or bleeding caused by excessive heat in the body.

• Hydrating and Nourishing: It boosts body fluids, easing thirst, constipation, or dryness from yin deficiency (a lack of cooling energy), often caused by stress or late nights.

• Supporting Overall Health: Modern research shows raw rehmannia strengthens the heart, promotes urination, lowers blood sugar, and fights oxidation. It also protects the liver, aids blood clotting, and may resist radiation or fungal infections.

Raw rehmannia is ideal for those feeling overheated, dehydrated, or dealing with symptoms like nosebleeds or skin rashes.

Raw Rehmannia（left）and Cooked Rehmannia（right）

Benefits of Cooked Rehmannia Root

Cooked rehmannia, made by steaming raw roots, is slightly warm, sweet, and targets the liver and kidneys. Its key benefits include:

• Nourishing Blood and Energy: It replenishes blood, helping with pale skin, dizziness, palpitations, or irregular periods caused by blood deficiency.

• Strengthening Kidneys: It eases sore backs, weak knees, hot flashes, night sweats, or premature graying from kidney yin deficiency, common in high-stress lifestyles.

• Boosting Vitality: It supports bone marrow and essence (vital energy), improving energy and resilience.

Cooked rehmannia is perfect for long-term nourishment, especially for those feeling weak, tired, or experiencing symptoms of low energy or poor circulation.

Cooked Rehmannia Root

Raw vs. Cooked: What’s the Difference?

Though both come from the same plant, raw and cooked rehmannia have distinct roles:

• Raw Rehmannia: Cold and cooling, it clears heat, cools blood, and hydrates. Think of it as a remedy for “hot” conditions like fever or rashes.

• Cooked Rehmannia: Warm and nourishing, it builds blood and strengthens kidneys. It’s best for “weak” conditions like fatigue or low vitality.

The transformation happens during processing. Raw rehmannia is dried to about 80% dryness, keeping its cooling nature. Cooked rehmannia is steamed, sometimes multiple times, turning it warm and sweet. Ancient texts like the Compendium of Materia Medica note this shift: raw rehmannia cools “hot blood,” while cooked rehmannia nourishes “weak blood.”

The transformation of rehmannia during processing.

Raw vs. Cooked rehmannia

Modern Uses and Science

Modern research highlights rehmannia’s active compounds, like catalpol, β-sitosterol, and mannitol. Raw rehmannia has more catalpol, which supports its cooling effects, while cooking converts some compounds into monosaccharides, doubling their content and enhancing nourishment. These compounds help:

• Stimulate blood cell production for better circulation.

• Protect the liver and lower blood sugar.

• Fight oxidative stress, benefiting heart health and diabetes management.

Traditional processing methods, like “nine steaming and nine drying,” have been simplified to one or three cycles, but they still preserve rehmannia’s core benefits.

Cooked Rehmannia

Precautions

When using rehmannia, keep these in mind:

• Quality Matters: Some commercial cooked rehmannia may include additives for color or sweetness, which can reduce effectiveness. Choose products that follow the Chinese Pharmacopoeia standards.

• Tailor to Symptoms: Use raw rehmannia for heat-related issues and cooked for nourishment. Consult a doctor to pick the right form.

• Moderation: Overuse or incorrect use may cause side effects, especially for those with specific health conditions.

  
  

Final Thoughts

Rehmannia root, whether raw or cooked, is a versatile herb with a rich history and modern relevance. Raw rehmannia cools and hydrates, tackling fevers and thirst, while cooked rehmannia nourishes blood and kidneys, boosting energy and resilience.

By understanding its forms and benefits, you can harness this “earth marrow” to support your health. Always consult a healthcare provider to use rehmannia safely and effectively, ensuring its ancient wisdom benefits your modern life.

Chinese Name	地黃
Chinese Pinyin	Dihuang
English Name	Adhesive Rehmannia Root Tuber
Latin Pharmaceutical Name	Rehmanniae Radix
Category	Roots and rhizomes
Origin	The fresh or dried tuberous rhizome of Rehmannia glutinosa Libosch.(Scrophulariabeae)
Production Regions	Primarily produced in the Chinese provinces of Shandong, Shanxi, Henan, Hebei.
Macroscopic Features	Xian di huang: Fusiform or cylindrical strip-shaped, 8~24cm long. Outer skin is thin, externally pale reddish-yellow, and with curved longitudinal wrinkles, scars of bud, horizontal long lenticels and irregular scars. Fleshy and easily broken; fractured surface is pale yellowish-white, orange-red oil spots can be seen, xylem is yellowish-white; faint odor; slightly sweet and bitter. Sheng di huang: irregular spherical or long spherical lumps, 6~12cm long, 3~6cm diameter; externally grayish-brown or grayish-black, whole body is wrinkled with irregular horizontal curves; thin ones are often flake-shaped, slightly flat and twisted; soft texture, firm after dried, heavy, difficult to break; fractured surface is smooth, purple-black or brownish-black and lustrous, oily and sticky; faintly aromatic odor; slightly sweet. Shu di huang: irregular lumps, segments, uneven size and thickness; externally brownish-black and lustrous and sticky; soft texture and pliable, difficult to break; fractured surface is brownish-black and lustrous; sweet taste.
Quality Requirements	Superior medicinal material of Xian di huang is reddish-yellow, thick and strong. Sheng di huang is large, heavy, brownish-black oily fractured surface and sweet. Shu di huang is large with brownish-black inner and outer surface and lustrous.
Properties	Xian di huang: sweet, bitter; cold. Sheng di huang: sweet, cold. Shu di huang: sweet, slightly warm.
Functions	Xian di huang: Clears heat, engenders fluids, cools blood, stops bleeding. Sheng di haung: clears heat, cools blood, nourishes yin, and engenders fluids. Shu di huang: nourishes yin, supplements bloods, boosts essence, and fills the marrow. Apply to yin deficiency and hectic fever, diabetes, hematemesis, non-traumatic hemorrhage, metrorrhagia, irregular menstruation, threatened miscarriage, diarrhea due to yin damage.
Processed Form	Shu di huang (Rehmanniae radix praeparata): Dried di huang stir with 30% yellow rice wine, steam to black and moisture, take out and dry. Or steam dried di huang for 8 hours and moisten overnight, resteam 4~8 hours on the next day and moisten overnight, take out and sun-dry 80% dry, slice and dry. Irregular lupms, black externally and enternally, wrinkles on outer surface. Soft texture; fractured surface is moisture, lustrous oily lumps in the center, very sticky; sweet taste. Nourishes yin, supplements blood. Apply to yin deficiency and anemia, relative weakness in the loins and knees, hectic fever and bone steaming, seminal emission, metrorrhagia, irregular menstrual periods, diabetes, frequent urination, deafness, and dizziness. Charcoal shu di huang: put shu di huang into calcined pot about 80% full and cover with one pot, sealed with yellow mud, press with heavy stuff, calcine with slow and fast fire till the paper on the cover pot turned into burnt yellow, block the fire, cool and take out; or straightly fry to charcoal. Promotes stop-bleeding and astringing functions.