In a dry skillet over medium heat, toast rice grains, stirring frequently until fragrant and just starting to color, about 4 minutes. Transfer to a bowl or jar and add 2 cups water. Set aside to soak for 10 hours.
When soaking is complete, pour rice and water into blender, add salt, sweetener (if desired) and vanilla (if desired), and blend at highest setting until rice grains are no longer visible, about 2 minutes (see note).
Using a nut milk bag set in a colander (or a similarly fine mesh strainer), strain milk into a bowl and transfer to a clean glass storage jar. Chill rice milk thoroughly before serving. Shake well before each use.
