48 hours. In catering service places, in order to carry out inspection, identification or analysis, it is necessary to keep a sample of some foods that are perishable, controversial or need to be tested. According to the relevant national laws and regulations "Product Quality Law", it is required that the food sample should be kept for no less than 48 hours, so that the problem food can be traced back in time and measures can be taken as soon as possible to ensure public health and safety.