Soak the soybeans inside a bowl with water overnight.
The next day, blend a small quantity of soybeans in a blender each time. Add enough water to cover them over. Blend well until smooth for about 2 minutes.
Transfer the batter formed through a nut milk bag over a large bowl and squeeze all the milk well.
Transfer all the remaining soy pulp to a different bowl. You can make meatballs or other delicious recipes from soy pulp, so you shouldn't throw them away.
Repeat the process of blending the soybeans in water and then squeezing the milk through a cheesecloth for the remaining soybeans.
Remove all the foam formed with a large spoon. Even during cooking, the milk will form foam.
Transfer the strained milk to a cooking pot. Remove the foam and close again with a lid. Cook for 15 minutes over medium heat. Make sure it's simmering and watch over the milk so it won't boil otherwise all the milk will spill.
Remove from the heat and leave inside the covered pot until cooled. Then transfer to a glass bottle with a hermetic closure. Keep refrigerated for up to a week.