日常在消費與飲食之前，檢視有效日期成為一種習慣性的社會行為，習以為常但並非理所當然，乃至於矛盾。基於此，本研究好奇有效日期這項制度於社會的現況為何？如何被實踐？試以眾人熟悉且店家數分布最密集的連鎖加盟便利商店—「7-Eleven統一超商」為代表性研究場域，其門市職員為面訪對象來源。研究發現到有效日期的實施與「食物浪費」之間的強烈關聯性，換言之，以「食物安全」為目的的有效日期，與「食物浪費」產生的對立、衝突，成為不可被忽略的事實。現代社會中，一方面面對著不時被討論、關懷的糧食危機議題，食物浪費的嚴重化成為最大的諷刺；另一方面食品危機層出不窮、屢見不鮮，對於食物安全的重視度成了最沉重的難題。 本研究試圖釐清「在有效日期制度存在之下，對於食物究竟可食與否，產生的兩難困境」：若不依據有效日期而食，「食物安全」令人堪憂疑慮；反之，「食物浪費」成了不得不的後果。本研究依序從制度、理性、價值面向來對此困境進行歸納與分析，最終歸結為下列五點：一、近年來，頻繁的食安風暴造成食物安全的要求加重，而易將仍可食用的食物拋棄；二、有效日期的氾濫使用致使消費者僅在意食物「過期與否」而非「可食與否」；三、越謹守有效日期所帶來的新鮮品質與安全保障，越能為業者製造更多正面名聲與商業價值；四、個人原本對於食物應負起的責任，因有效日期而轉移到整體社會來承擔，使得人們對於「食物浪費」顯得無感與忽視；五、買賣雙方對有效日期的意義認知有一定差異，前者視為「預期性安全」，後者作為「必然性浪費」。 時至今日，有效日期這項制度在社會建構下的結果，改變了社會與食物之間的關係，冀望此研究作為現代社會的反思基礎，並共同致力於未來出路。 / Checking for the expiry date before buying or eating anything, has to be one of the habitual behaviors in our daily life. This act seems usual, but actually is not necessary at all and is even a contradiction. Based on this reasoning, this research is about how the system of expiration date is being used nowadays and how it is being implemented. Through participant observation and in-depth interviews, collecting view points and experience from staff members in 7-ELEVEN President Chain Store, which is known for the most branches of convenience retailer in Taiwan. The research found that there is a robust relation between the implementation of expiration date and serious “food waste”. It means that the system of expiration date, which is for the purpose of ensuring “food safety”, will also come about vast amounts of “food waste”. Comparing with the global food crisis, “food waste” is not only a great irony but also conflicts with the maintenance of “food safety”. In view of this, the objective of this research lies in clarifying that food is edible or not will be a dilemmatic situation under the system of expiration date. If people don’t follow the expiration date it compromises “food safety”, otherwise “food waste” will be the consequence without choice. Whereas this dilemma, the research is going to integrate and analyze it sequentially via three dimensions, including system, rationality, and value. There are five following conclusions: (1) Recently, the frequent food safety issues raise the demand of safety, so it’s easier to abandon edible food. (2) Overusing the expiration date makes the consumer only focus on if food is “overdue or not” but not “edible or not”. (3) For businessmen, adhering to the expiration date more results in having more positive prestige and benefits. (4) Because of the expiration date, the responsibility of food for the individual shifts onto the whole society. (5) The understanding of expiration date between buyer and seller are different. The former views it as “Precautionary safety”, while the latter is to regard it as “Inevitable Waste”. Hopefully this research will provide reference for reflecting on the relation between society and food, and aid in finding a solution in the future.