postum is an instant type beverage used in place of coffee. it made from roasted grains and molasses. postum history goes back to 1895 when an american named c.w. post created the coffee substitute, inspired by a caramel coffee recipe made by harvey kellogg. it reached the height of its popularity during world war ii. it also really caught on with people who for health or religious reasons preferred not to consume drinks that contained caffeine. for popular usage on the sitcom seinfeld george says to jerry he does not know why postum is not a more popular beverage.