剩菜到底能放几天？USDA食品安全口径：冰箱不高于华氏40度，剩菜3到4天内吃完、复热到165度
做一顿吃两顿是很多家庭的日常，但剩菜在冰箱里到底能放几天，美国农业部（USDA）食品安全检验局和联邦食品安全门户 FoodSafety.gov 给出过明确口径，数字并不复杂。
第一是温度。冰箱冷藏室应保持在华氏40度（约摄氏4度）或以下，冷冻室为华氏0度（约摄氏零下18度）。温度不够低，细菌繁殖速度会明显加快；USDA建议在冰箱里放一个温度计核对，而不是只凭旋钮刻度。
第二是时间。熟食剩菜要在烹饪后2小时内放进冰箱——如果室温高于华氏90度（约摄氏32度），这个时限缩短为1小时。放进冰箱的剩菜应在3到4天内吃完；冷冻可以长期保住安全性，但风味和质地一般在2到6个月内较好。
第三是复热。剩菜再次加热时，整份食物要热到华氏165度（约摄氏74度），汤汁类要煮沸；微波加热时中途搅拌、静置一两分钟，让热量分布均匀。
第四是分装。用浅口容器分装剩菜，冷却和冷藏都更快；吃多少取多少，反复整盒加热又放回，会额外增加风险。以上口径出自 USDA 与 FoodSafety.gov 的剩菜保存指引。（来源：美国农业部食品安全检验局、FoodSafety.gov 公开指引）
How Long Do Leftovers Keep? USDA Food-Safety Numbers: Fridge at 40°F or Below, 3 to 4 Days, Reheat to 165°F
Cooking once and eating twice is routine in many households, and the U.S. Department of Agriculture's Food Safety and Inspection Service and the federal FoodSafety.gov portal publish clear numbers for how long leftovers keep.
Temperature comes first: a refrigerator should be held at 40°F (about 4°C) or below, and a freezer at 0°F (about −18°C). The USDA advises checking with an appliance thermometer rather than relying on the dial.
Time comes second: cooked leftovers should be refrigerated within two hours of cooking — within one hour if the room is above 90°F (about 32°C). Refrigerated leftovers should be eaten within three to four days. Freezing keeps food safe indefinitely in safety terms, though quality is best within two to six months for many cooked dishes.
Reheating comes third: leftovers should be reheated to 165°F (about 74°C) throughout, soups and sauces brought to a boil, and microwaved food stirred and rested so heat distributes evenly. Finally, the guidance calls for storing leftovers in shallow containers so they chill quickly, and taking out only the portion to be eaten rather than reheating and re-chilling the whole container repeatedly. (Source: USDA Food Safety and Inspection Service and FoodSafety.gov guidance)
图片来源：冰箱中的蔬果，CC0（Wikimedia Commons，摄影：Alabama Extension）
