Ghouls And Food

So this is something thats been bothering me since I first got into Tokyo Ghoul. (got into it very recently) So Ghouls cant eat human food right? They are able to drink coffee for some reason. So since Coffee has milk and other stuff wouldnt that mean they are able to consume anything with a dairy product like cheese ice cream and such? Or because of the mixing of items to make the coffee make it consumable for ghouls?