不少罐頭食品的保存期限長達兩三年，甚至更久。很多人以為是加入大量防腐劑，其實真正令罐頭耐放的秘密，並不是防腐劑，而是密封與高溫殺菌技術。
Many canned foods remain safe to eat for several years, leading people to assume they’re packed with preservatives. In reality, their remarkable shelf life comes from advanced sealing and heat-processing methods rather than chemical additives.
中文版本
每當打開一個罐頭，不少人都會好奇，為什麼裡面的食物放了幾年仍然可以食用？其實，罐頭食品之所以能夠長時間保存，主要依靠的是食品加工技術，而不是大量添加防腐劑。現代罐頭製造流程十分嚴謹。食物經過清洗、切割及預先處理後，會放入金屬罐或玻璃瓶內，再加入適量湯汁、糖水或油脂，然後利用機器將容器完全密封。密封完成後，整個罐頭會放進高溫高壓設備內進行加熱，通常溫度超過攝氏一百一十度，部分產品甚至高達一百二十一度。這個過程稱為商業無菌處理，可以有效消滅大部分細菌、霉菌及可能產生毒素的微生物，包括耐熱性較高的細菌孢子。完成殺菌後，密封的罐頭幾乎沒有空氣進入，外界細菌亦無法再次污染食物，因此即使放置多年，只要罐身保持完整，食物仍能維持安全。許多人誤以為罐頭一定加入大量防腐劑，其實大部分罐頭食品根本毋須依靠防腐劑保存，因為真正發揮作用的是密封及高溫殺菌。當然，保存期限並不代表品質永遠不變。隨著時間過去，食物的色澤、口感及部分維生素可能慢慢下降，但只要包裝沒有生鏽、膨脹、破損或漏氣，並按照標示方式存放，一般仍能保持良好品質。如果發現罐頭頂部鼓起、打開時有異味、內容物變色或噴出氣體，就應立即丟棄，因為這可能代表細菌已經滋生。原來，一個小小的罐頭，結合了食品科學、金屬加工及殺菌技術，不靠大量防腐劑，也能讓食物安全保存多年，成為人類最成功的食品保存發明之一。
English Version
It can be surprising to discover that a can of soup, vegetables, or fish may stay shelf-stable for several years. The secret isn’t an abundance of preservatives but a carefully controlled preservation process developed through food science. Before sealing, the food is cleaned, prepared, and placed into a metal can along with liquid such as water, broth, oil, or syrup when needed. The container is then tightly sealed so outside air cannot enter. After sealing, the cans are heated under pressure at temperatures high enough to destroy microorganisms that could spoil food or cause illness. This process, often called commercial sterilization, eliminates bacteria, molds, yeasts, and even many heat-resistant spores. Once the food has been sterilized and the container remains airtight, microorganisms cannot easily re-enter, allowing the contents to remain safe for a very long time without refrigeration. This is why many canned foods require little or no added preservatives. While the food remains safe, its quality slowly changes over time. Colors may become duller, textures softer, and some vitamins gradually decrease, but the product can still be perfectly edible if stored properly. However, damaged cans should never be ignored. A swollen lid, leaking seam, heavy rust, unusual odor, or contents that spray out when opened can all indicate bacterial growth, making the food unsafe. The humble food can is therefore much more than simple packaging. It is the result of decades of innovation in engineering, microbiology, and food preservation, allowing millions of people around the world to store nutritious food safely for years while reducing waste and improving food security.
總評
中文
罐頭能保存多年，真正原因是密封技術配合高溫殺菌，而非大量防腐劑，是食品科技的重要成果之一。
English
The long shelf life of canned food comes from airtight sealing and heat sterilization, making it one of the greatest achievements in modern food preservation.
