Set glass jar in the refrigerator to steep for 12 - 18 hours. Place a mesh strainer lined with a coffee filter over a medium-sized bowl. Pour the brewed coffee into the coffee filter and allow to slowly strain.
This may take up to 15 minutes. Discard the coffee grounds in the trash can (not down a garbage disposal). Transfer cold brew coffee concentrate to a small bottle or jar with a resealable lid. Store in the refrigerator for 7 - 10 days.