Soak 1 cup dried soybeans in plenty of water for 8 to 12 hours
Drain and rinse the soybeans
Remove the skins if desired
Add the soaked soybeans to a blender with 4 cups fresh water
Blend until smooth
Pour the mixture into a large pot
Cook over medium heat, stirring often
Bring to a gentle boil, then reduce heat and simmer for 15 to 20 minutes
Skim off any foam that forms on top
Strain the mixture through a nut milk bag, cheesecloth, or fine sieve
Squeeze out as much liquid as possible
Return the soy milk to the pot if needed
Add sweetener or flavoring if desired
Cool completely
Refrigerate and use within 3 to 5 days