Douzhir (Beijing Fermented Mung Bean Drink)

Rinse 1 cup dried mung beans and soak in 2 cups of water for 4 hours until fully expanded and soft.

Drain the soaking water. Gradually add the beans to a blender along with 4 cups of water, blending until smooth and creamy.

Strain the mung bean mixture through a fine cheesecloth, squeezing out the liquid. Reserve the pulp for other uses (like mung bean patties).

Let the strained liquid sit for 2 hours to allow starch to settle. Carefully pour off the top clear water, leaving the thick starch paste at the bottom.

Transfer the starch paste to a clean fermentation container. Add about 1 cup of water and stir. Cover with a lid, leaving a small gap for air. Ferment at 25-30°C (77-86°F) for 24-48 hours until bubbles appear and it smells sour.

After fermentation, the mixture separates into a clear sour liquid on top and starch on the bottom. Pour the sour liquid into a pot (avoid disturbing the sediment), add some water (ratio 2:1 sour liquid to water), and bring to a boil over high heat.

Reduce heat to low, skim off any foam, and continue cooking for 5-10 minutes until the surface is frothy and the color turns gray-green with a fragrant aroma.

Ladle the cooked douzhir into bowls. It can be seasoned with a pinch of salt or sugar if desired, but traditionally served plain, accompanied by jiaoguai (fried dough rings) and shredded pickled vegetables.