At Tyler Malek's ice cream parlors, one cook's trash is another chef's frosty treat. The head ice cream maker at the Portland, Oregon-based Salt & Straw uses the whey leftover from yogurt makers in upstate New York to make his lemon curd flavor. For chocolate barley milk, he mixes in the remnants of rice and grains from beer brewing to give it a light and creamy taste. "Instead of calling this food waste, we need to call it wasted food and start decreasing how much wasting we're doing," Malek said. Malek's ice cream chain is among those at the forefront...