綠豆湯 (Lu Dou Tang)

Mung beans (綠豆) [1] are a type of legume commonly found in the cuisines of both East and South Asia. In Chinese cooking, mung beans are used in a variety of ways. They can be turned into mung bean starch, which can be made into pancakes or cellophane noodles. Mung bean sprouts are also a commonly eaten vegetable. The beans themselves, either whole or ground into paste, are often sweetened and used in desserts, such as sweet zongzi, mooncakes, or, more recently, ice cream. Today, however, we will be making mung beans in perhaps their simplest form, a chilled dessert soup. Whole mung beans are packed full of protein, vitamins, and minerals, making this both a delicious and nutritious treat on a hot summer day! [2]

Ingredients

1 cup dry mung beans
¼ cup sugar or to taste
¼ tsp salt
8 cups water

Begin by washing 1 cup of dry mung beans, and soaking them in 2 cups of water. They should soak for at least 2 hours, and up to overnight. The beans will absorb some of the water, reducing cooking time. More importantly, hydrating the starches in the beans will give us a smoother and more consistent texture in the final soup. The beans will swell a bit, and some may split—this is normal!

When the mung beans are soaked, add them and their soaking water to a large pot. Add 6 additional cups of water, bringing the total water to 8 cups. Adding a pinch of salt helps accentuate the natural fragrance of the mung beans, and add the sugar as well. Mung beans on their own have a subtle and fragrant flavor, but are not very sweet. The sweetness of this soup comes almost entirely from the sugar. My personal preference is for about ¼ cup of sugar for this much soup, which lends the soup a subtle sweetness. However, you should adjust the amount of sugar to your taste. It’s worth noting that in restaurants, this soup is generally made with closer to a full cup or even a cup and a half of sugar.

Bring the pot to a boil, and simmer the soup, covered, for 40-60 minutes, or until the beans have softened and many have split. The starch released by these beans will slightly thicken the soup. Don’t cook the soup for longer than an hour, as the beans will lose their green color and start to dissolve. Stir the soup well and taste for seasoning. Then let the soup cool to room temperature before moving to the refrigerator to chill. [3] Chill for at least 2 hours, or until cold. Stir the soup well just prior to serving, and serve chilled. Mung bean soup also freezes well, for longer term storage.

Substitutions

Some variations of this soup will include barley, tapioca pearls, or sago pearls. If you’re using any of these additions, add them with the beans at the start of the simmer. Be aware that you may have to add additional water, especially for the pearls.

You can add a couple slices of ginger to the pot to infuse the soup with a slight ginger flavor. Substituting honey for some or all of the sugar is also a welcome addition. Both ginger and honey will change the flavor profile of the soup.

If you are using a pressure cooker, you can skip the soaking and reduce the cooking time to 20 minutes.

[1] 綠豆 (“lu dou”) translates directly to “green bean” in Chinese. The English name for the legume, “mung,” is derived from the Hindi word मूंग ("moong"), which is itself from the Sanskrit मुद्ग ("mudga").

[2] Traditional Chinese medicine classifies foods into either “warming” or “cooling” categories. Some of these make intuitive sense—spicy foods are “warm,” and most fruits are “cool.” Others make less sense—red meat, chocolate, and rice are “warm,” while tea and seafood are “cool.” Many Chinese dishes try to combine warm and cool ingredients, but in the summer, it is advised that you eat “cooling” foods. Mung beans are considered one of the coldest foods.

[3] In general, it isn’t a good idea to place any large, hot object directly into the refrigerator, as the heat from it can raise the temperature inside the refrigerator to dangerous levels. This is particularly true of soups, as liquid water has an incredibly high heat capacity: 4.18 J/(g K).

Recipe

Prep Time: 5 min Cook Time: 45 min Total Time: 50 min
(+4 hrs inactive) (5 hrs)

Difficulty: 1/5

Heat Sources: 1 burner

Equipment: pot

Servings: 8

Ingredients

1 cup dry mung beans
¼ cup sugar or to taste
¼ tsp salt
8 cups water

Instructions

1. Soak the dry mung beans in 2 cups of water for at least 2 hours, or overnight. The beans will swell and some may split.

2. Add the mung beans and their soaking water to a large pot. Add the sugar, salt, and 6 additional cups of water, and bring to a boil. Simmer for 40-60 minutes, or until the mung beans are soft and many have split.

3. Let the soup cool to room temperature, then refrigerate until chilled.

4. Stir well and serve cold.