Quality of ingredients used

As a coffee ***** I occasionally pass by Seattle and have spent thousands of rands at their little store in one of the caltex garages. I really do enjoy the quality of the beans used, although this time while I was in a hurry to go write an exam I took a few sips in the car and the milk was completely sour... After taking several tastings I definitely realized it was the coffee and not me. Hours after this I didn't feel well at all due to the lack of this ingredient. I understand that milk can go sour but perhaps an employee should sample it before using to pour into a quality coffee such as Seattle, we're already spending a lot of money on a hot drink not to mention the recent price increases.