How are 'high-tech' box lunches on bullet trains made? (6)

While cooking, the temperature of the food has to be kept above 85 degrees Celsius, and below 10 degrees Celsius while packing. Train attendants then serve the food after heating them in the microwave. The most difficult part of making box lunch for bullet trains is how to keep the good taste of the dish after a sudden temperature drop. Cooks had tied countless times to come up with the best choice with materials and processes. (Photo/Cri.cn)