Ever since phosphates were eliminated from dishwasher detergents in the summer of 2010, consumers have been complaining about "clean" dishware coming out of the dishwasher covered in a white film or metal that's been discolored. Because phosphates foul waterways, they were banned in many states. Major manufacturers responded by reformulating their products for all 50 states eliminating all but trace amounts from dishwasher detergents. (Laundry detergents were already phosphate-free.)
Phosphates help to control water hardness, according to the American Cleaning Institute. They also boost a soap's ability to clean and prevent food particles from sticking to the dishes. Without it, dishes can emerge from the dishwasher with bits of food still attached, glassware filmed in white and aluminum that's tarnished.
The chorus of complaints we heard from readers after the switch caused Consumer Reports to recalibrate its dishwasher detergent tests. In the new tough test we take a set of clean glass dishware and uncoated aluminum sheets and wash them 20 times, simulating more than a month of machine washing, using the same detergent and with water that's harder than most. Our revised tests of tablets, pacs, liquids, gels, and powders changed the rankings of some products.
We also test the cleaning ability of the detergents by smearing dishware with a "monster mash" of sticky foods such as chocolate pudding, peanut butter, rice, and macaroni and cheese, while pots received just the macaroni-and-cheese blend. We baked on the goo and assessed how well each detergent removed the food, kept it from being redeposited, and avoided leaving water spots. A key lesson from out tests was not to shop strictly by brand, as different products from the same brand wound up near the top and bottom of the Ratings.
The best detergents cleaned well without leaving film on the glassware or discoloring the aluminum. This matters most in areas with hard water, which is more than half of the country. If your home has soft water, you can consider detergents that scored well for cleaning and pay less attention to the hard-water test results.