Phosphate-free detergents have been on the market for a while now, and although we've found many that clean well, some readers aren't happy. They've complained to us about a buildup of white residue on dishware over time. As a result, we started a new test in which 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 very hard water. (Only 12 of the rated products have been subjected to that new test so far, so it was not a factor in our overall scoring, though we note our early findings in the Ratings, which are available to subscribers.)
Results of the tough new test showed that readers might have a reason to complain about some products. Method Smarty Dish, a very good cleaner otherwise, eventually turned our glassware milky white, as did the bottom-rated 365. And aluminum sheets discolored after we washed them repeatedly in those two products. Top-rated Finish Quantum, the mediocre Biokleen, and the subpar Finish Powder and The Laundress made our clear glassware somewhat filmy by the end of our test. Aluminum discolored after repeated washings with The Laundress and Finish Powder, though not with Biokleen and Finish Quantum. The coatings didn't etch the glass, but the worst of them required lots of scraping to begin removing the residue.
To rate a detergent's cleaning ability, we mix chocolate pudding, peanut butter, cream cheese, and more than a dozen other ingredients, refrigerate that goop, apply it to dinner plates, bake it on, and let it harden before the plates go into the same model dishwasher. For pot-cleaning, we make a batch of macaroni and cheese, mash it up, and smear it into 1-quart stainless-steel pots. Then we bake and cool the pots and put them in the dishwasher.
With each detergent, we also check for water spotting and redepositing of soil.