How we tested
Warming trays are portable flat surfaces that are designed to keep food piping hot as it sits out. They plug into the wall like electric griddles and, after preheating for about 10 minutes, can be topped with fully cooked food, either directly on the tray or in a serving vessel.
We loaded four models (from about $40 to about $125) with a saucepan of tomato soup, a ceramic dish of spinach-artichoke dip, a glass casserole of macaroni and cheese, and small quiches set directly on the trays, tracking their temperature over 4 hours to see if they remained above the food safety threshold of 140 degrees. We also noted how easy they were to handle and clean.
One model was a complete failure, allowing foods to cool to a lukewarm 128 degrees after just 1 hour. We became wary of another model when its metal sheet popped in and out during use and its heating element burned light marks onto the steel surface after just a few uses. But we found two models worth considering. One featured a heat setting that kept food hot in all but the deepest pots—and its low price earned it our Best Buy recommendation—while the other offered a range of heat settings, the highest of which did a better job in our final head-to-head test: keeping a Dutch oven full of chili piping hot for 4 hours.