When the food you consume is burned in the body, it yields a mineral residue called "ash." This ash can be either acidic or basic (alkaline) in reaction depending on whether the food burned contains mostly acidic or basic ions.
The reaction of the urine can be changed definitely by drinks (like orange juice). Most fruits and vegetables give an alkalized ash and tend to make the urine alkaline, but there are some exceptions. Meats and cereals usually produce an acidic ash that will acidify urine. Some acid-producing examples are: breads (especially whole wheat), cheese, corn, crackers, cranberries, eggs, macaroons, nuts, pastries, rice, prunes, meat, milk, bananas, beans (lima, navy), beets, greens and spinach. Some neutral foods are: butter, coffee, grease, honey, salad, oils, syrups, tapioca and tea. Watch your diet - Mother Nature knows what she is doing.