Fu ru kong xin cai (腐乳空心菜) — water spinach stir-fried with fermented bean curd — is the ultimate quick Hunan home-style green vegetable. Just a handful of ingredients, three minutes in a hot wok, and you have a side dish that is intensely savory, pungent, salty, and somehow absolutely addictive. The strong, cheesy fermented bean curd transforms simple greens into something with real depth and character. It is quick, cheap, and goes with everything — the very definition of peasant food at its best. If you have ever wondered how Chinese restaurants make plain greens taste so good, this is one of their secrets.
Furu kong xin cai (腐乳空心菜) is a perfect example of Xiangjiang River school home cooking at its most elemental: cheap ingredients, maximum flavor, zero fuss. Fermented bean curd (fu ru, 腐乳) is one of the great umami weapons in the Chinese pantry — cubes of tofu that have been fermented with mold cultures, then brined in rice wine and salt. The result is something like a cross between blue cheese and miso — salty, pungent, creamy, and packed with umami. A single cube is enough to flavor a whole plate of greens. Water spinach (kong xin cai, 空心菜, literally "hollow heart vegetable") — also known as ong choy, morning glory, or kangkong — is the ideal vehicle: its hollow stems and tender leaves absorb the savory fu ru sauce perfectly, and its slight bitterness balances the saltiness. This is the kind of dish that Hunan families eat at almost every dinner — a quick green vegetable to round out a meal of rice and a main dish. It is not glamorous, it is not complicated, and it is one of the most delicious things you can make in under 5 minutes.
Ingredients
The ingredient list could not be shorter. The quality of the fermented bean curd and the freshness of the greens are what matter most.
- Water spinach — 300 g. Also called kong xin cai, ong choy, morning glory, or kangkong. Look for bunches with bright green leaves and firm, crisp stems. Avoid any that look wilted or yellowed.
- White fermented bean curd — 2 cubes. Also called bai fu ru or white furu. This is the mildest variety. Look for it in glass jars at Asian grocery stores, usually near the tofu and pickled vegetables.
- Garlic — 2 cloves. Fresh garlic, thinly sliced. It infuses the oil with aroma.
- Dried red chilies — 2. For a bit of heat and color. Tear them into pieces before using.
- Cooking oil — 2 tablespoons. Use a high-smoke-point oil like peanut oil, canola oil, or vegetable oil.
- Chinese rice wine — 1 teaspoon. Shaoxing wine or mijiu (Taiwanese rice wine) both work. It helps loosen the fu ru paste and adds depth.
- Sugar — just a pinch, to balance the saltiness of the fermented bean curd.
Step-by-Step Instructions
- Wash and trim the water spinach. Water spinach grows in water and tends to have a lot of sand and dirt hidden in its hollow stems and curled leaves. Wash it thoroughly in several changes of cold water — swish it around, lift it out, and change the water until the water runs clear. Trim off and discard the thick, tough lower stems (the bottom third or so). The upper stems and leaves are what you want. You can leave the tender stems whole or cut them into 5 cm sections. Dry the greens as well as you can — use a salad spinner or pat them dry with a clean kitchen towel. Wet greens will steam in the wok instead of stir-frying, resulting in mushy, dull-colored greens. Dry greens sear and stay bright green.
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Mash the fermented bean curd with rice wine. Pop 2 cubes of white fermented bean curd into a small bowl. Add 1 teaspoon of rice wine. Mash them together firmly with the back of a spoon until you have a smooth, creamy paste with no lumps. This is an important step — if you just drop whole cubes into the wok, they will not distribute evenly and you will get clumps of concentrated fu ru. Mashing it first ensures that every bite gets an even coating of that savory, pungent flavor. Set the paste aside.
Fermented bean curd is very salty
Fu ru is intensely salty — it is a preserved food, after all. Two cubes is plenty for 300 g of greens. You almost certainly will not need to add any additional salt. Taste before seasoning — if you think it needs more, add just a tiny pinch. It is easy to add more salt; it is impossible to take it away. The pinch of sugar is important too — it does not make the dish sweet, it balances the salt and rounds out the fermented flavor.
- Heat the wok until screaming hot. Place your wok on the stove over the highest heat you have. Let it heat up for at least 2 minutes — you want it genuinely hot, almost to the point of smoking. This is the single most important tip for good stir-fried greens. A hot wok sears the outside of the vegetables instantly, locking in color and creating that smoky wok hei flavor. If the wok is not hot enough, the greens will steam instead of sear, and they will turn dark and mushy. Add the oil and swirl it around to coat the sides of the wok. The oil should shimmer and look thin and runny.
- Stir-fry garlic and dried chili. Add the sliced garlic and the torn dried red chilies to the hot oil. Stir them around with your spatula for about 10 seconds — just until the garlic turns a pale golden color and you can smell its aroma. Do not walk away. Do not get distracted. Garlic goes from golden to burnt in literally 3 seconds, and burnt garlic is bitter and will ruin the whole dish. The goal here is to infuse the oil with garlic and chili flavor — that flavored oil is what coats every piece of spinach and makes it taste so good.
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Add water spinach and fu ru paste, toss fast. Dump all of the water spinach into the wok at once. Drizzle the fu ru paste over the top. Now, using your wok spatula, toss everything together as fast as you can — lift, turn, fold, repeat. Keep the heat on high. The greens will wilt dramatically in the first 30 seconds. Keep tossing for another 15 to 30 seconds, until all of the leaves are wilted but the stems still have a bit of crunch. Total cooking time from when the greens hit the wok: 45 to 60 seconds. That is it. Add a pinch of sugar and give it one last toss. Turn off the heat immediately.
High heat, fast toss — do not overcook
The biggest mistake people make with stir-fried greens is overcooking them. Water spinach cooks in under 2 minutes. If you cook it for 5 minutes, it will be dark green, mushy, watery, and bland. The ideal texture is bright green, just wilted, with stems that still have a slight snap to them. It should look vibrant, not dull. If you are unsure, err on the side of undercooking — the residual heat in the wok and the plate will continue to cook the greens for another minute after you turn off the heat.
- Serve immediately. Transfer the greens to a plate and serve right away. Stir-fried greens are at their best within the first minute or two out of the wok — they continue to wilt and lose color as they sit. This is a side dish, not a main course — serve it alongside rice and a main dish like Hunan stir-fried pork or beer duck. The salty, pungent, savory flavor of the fermented bean curd cuts through rich, fatty dishes perfectly. It is the kind of simple green that makes you want to eat more vegetables — and more rice.
Fermented bean curd (腐乳, fu ru), also called fermented tofu or preserved bean curd, is a traditional Chinese fermented food with a history of over 1,500 years. It is one of the most important umami seasonings in Chinese cooking. Here is what you should know:
- How it is made. Firm tofu is cut into small cubes and inoculated with a mold culture (usually Actinomucor elegans or Mucor species). The cubes ferment for several days, developing a fuzzy white coating. Then they are brined in a mixture of salt, rice wine, and often other seasonings like chili, sesame oil, or five-spice powder, and aged for weeks or months.
- What it tastes like. Fu ru has a strong, pungent, salty flavor that is often compared to blue cheese — creamy, savory, and intensely umami. The texture is soft and spreadable, like a soft cheese. The flavor is concentrated, so a little goes a very long way.
- White vs red. White fermented bean curd (bai fu ru, 白腐乳) is the mildest variety, fermented with white mold and brined in rice wine. Red fermented bean curd (hong fu ru, 红腐乳) gets its color and flavor from red yeast rice (hong qu), which gives it a deeper, more complex flavor and a reddish-brown color. White is used for stir-frying greens; red is often used for braising meat.
- How it is used. Fu ru is never eaten plain — it is always used as a seasoning. It is commonly stirred into congee, used as a dipping sauce, mashed into stir-fry sauces, or added to braised dishes for depth. It is also a popular condiment at the breakfast table, served with rice porridge.
- Health benefits. Like other fermented foods, fu ru contains probiotics and is easier to digest than regular tofu. The fermentation process also increases the bioavailability of certain nutrients. In traditional Chinese medicine, it is believed to strengthen the spleen and aid digestion.
Substitutions & Adjustments
This is one of the most flexible recipes in the Hunan repertoire. Change the greens, change the heat, change the seasoning — it always works.
Less spicy
Omit the dried red chilies entirely — the fermented bean curd and garlic provide plenty of flavor even with no heat. If you want just a hint of heat, use one chili and remove the seeds. The dish does not need to be spicy to be delicious.
Ingredient substitutes
- No water spinach: Use regular spinach (cooks even faster — 30 seconds max), baby bok choy, choy sum, gai lan, Swiss chard, or kale (cut into thin ribbons). Adjust cooking time based on the green — tougher greens need longer, tender greens need less.
- No fermented bean curd: The closest substitute is white miso paste — use 1 teaspoon of miso thinned with a bit of rice wine or water. It will not be the same, but it provides a similar salty-fermented umami. You can also use oyster sauce or soy sauce, though the flavor profile will be different.
- No rice wine: Use a splash of dry sherry, mirin, or even just water to thin the fu ru paste. The wine adds depth but is not essential.
- Add more flavor: For extra richness, add a splash of oyster sauce along with the fu ru. For extra heat, add a teaspoon of chopped fresh chili or a drizzle of chili oil. For extra garlic, double the garlic — it is hard to have too much garlic with greens.
Make ahead
Do not make this ahead. Stir-fried greens are at their absolute best the moment they come out of the wok. They lose color, texture, and flavor within minutes. Prep the greens and the fu ru paste ahead of time, but cook them at the last minute — it only takes 3 minutes.
Storage
Leftover stir-fried greens are not great — they become mushy and lose their bright color. If you have leftovers, they will keep in the fridge for a day and can be reheated briefly in a hot wok, but the texture will not be the same. It is better to make just enough for one meal. An unopened jar of fermented bean curd keeps for years in the pantry; once opened, store it in the fridge where it will keep for at least 6 months.
Nutrition
Estimated values per serving (recipe serves 2). This is a light, low-calorie side dish — most of the calories come from the cooking oil. Water spinach is a good source of fiber, vitamin A, vitamin C, and iron.
| Nutrient | Per serving |
|---|---|
| Calories | 120 kcal |
| Protein | 4 g |
| Total fat | 9 g |
| Saturated fat | 1 g |
| Carbohydrates | 6 g |
| Sodium | 420 mg |
| Sugar | 2 g |
Values are estimates based on standard ingredient databases. Actual nutrition will vary depending on the amount of oil you use and the specific brand of fermented bean curd.
Frequently Asked Questions
Related Recipes
If you love this quick, flavorful Hunan green vegetable, these other home-style classics use the same high-heat stir-fry technique and pantry staples.