Mung Bean, Kelp and Rue Herb Sweet Soup 臭草海帶綠豆沙 (Cantonese: cao cho hoi dai luk dou sha) is a traditional Cantonese sweet soup. Sometimes it’s made without the kelp but mung bean and rue herb are always together. The strong aroma of the rue herb balances the mild flavour of the mung beans. People say that rue herb to mung bean is like dry mandarin peel to red bean or tong choy to preserved bean curd.
The mung beans are really the supporting cast in this show. The star is the rue herb or “Stink Grass”. I was reluctant to smell it at first because of the name. But when I took a whiff of it, I quite liked it! It was a strong scent, but not a bad scent. When it’s in the soup, the scent is much milder. Unfortunately, rue herb is not readily available at grocery stores here in Vancouver. Luckily for me, my mom grows it in her garden. I found the seeds for sale on Amazon and they are very easy to grow. If you know of someone who has some, you only need a branch/stem, put it in some water to grow some roots and then stick it in the soil. I’m going to grow some in my garden too.
Rue herb has many health benefits as per both Chinese and European herbology. It helps with menstruation, detoxification, respiratory issues, headache, arthritis, swelling and so much more. Together with mung beans, they are good for skin, heatiness (下火) and expels dampness (去濕) just to name a few. Furthermore, kelp is also good for skin. It’s high in antioxidants which fights free radicals and helps to prevent cancer and heart disease. Please note that this is general information about the ingredients. There may or may not be any studies to make conclusions. Please consult with your healthcare provider for advice.
Mung Bean, Kelp and Rue Herb Sweet Soup 臭草海帶綠豆沙 is NOT recommended for pregnant women because it is deemed to be too “cold 寒涼”. If you generally have cold limbs, you shouldn’t have too much of it either. A method to reduce the coldness of this dessert is to toast the mung beans with some uncooked rice in a wok before boiling it in water. Adding rice will make it more porridge-like and add some heat to balance the cold. (If adding rice, add ¼ of the weight of the mung beans). It is also not advised to consume Mung Bean, Kelp and Rue Herb Sweet Soup 臭草海帶綠豆沙 on an empty stomach.
My limbs are generally more hot than cold. And so, I love adding some Mung Bean, Kelp and Rue Herb Sweet Soup 臭草海帶綠豆沙 to vanilla ice cream and grass jelly. I made it with more texture and less broken so that when I put it on ice cream, it’s not too mushy. In my recipe, I’ll show you how to make it very smooth and broken down or soft but not as broken. Either way, I’m sure you’ll find it cooling and refreshing.
Another one of my favourite sweet soups is the Asian Pear Peach Resin Sweet Soup 雪梨桃膠糖水, give it a try!
Mung Bean, Kelp and Rue Herb Sweet Soup 臭草海帶綠豆沙
Ingredients
- 250 g Mung beans
- 20 g Dry kelp
- 20 g Rue herb (aka Common Rue, Ruta Graveolens, Stink Grass)
- 5 g Dry mandarin peel
- 2 L Water
- 1-2 slabs Brown rock sugar (aka pian tang/peen tong, slab sugar, approx. 80g/slab)
Instructions
- Soak green beans for 1 hour in water
- Soak kelp and mandarin peel for 30 minutes separately
- After 30 minutes, rinse kelp
kelp has a natural powder-like white substance that forms on it; it’s not mold. After soaking, it will be slippery, so be careful when you’re slicing it - Take half of the kelp, fold and slice into thin strips.
I usually discard the other half after cooking because I can’t eat that much but I want the jelly-like substance that it gives to the soup. Of course, you may also julienne all of it as well. 
- For the mandarin peel, use a knife and scrape off the white parts which may add bitterness to the soup
- Bring 2 L of water to a boil. Add mung beans, kelp, rue herb and mandarin peel. Bring to a boil again. Lower the heat to medium so that it is at a simmering boil
You want there to be some bubbles and the mung beans should be moving around in the water. Cook for 60 minutes, give it a stir every 20 minutes This cooking time will give you very broken mung beans. The finished product in the photos have the mung beans being less broken. This is because I wanted to add it to vanilla ice cream and grass jelly. If you’d like to do this too, cook for 30 minutes on medium (instead of 60 minutes) and then 20 minutes on low - When 60 minutes are up, remove the large pieces of kelp, mandarin peel and rue. Discard
- Turn heat to low and add sugar. Cook for 15 minutes
- Taste test. Add more sugar if necessary. Cook until sugar dissolves
- Serve hot or cold
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