The reason why canned herring smells so bad is that only the fish head and internal organs are removed in the process of making canned herring. After cleaning, soak it in salt water for a period of time, then cook it with low heat, and then put it in a can for natural fermentation for several months. Therefore, only canned herring smells so bad, and according to experimental research, the taste of canned herring is 3 times that of natto. Canned herring is so smelly because this food is made in a unique way. The production of canned herring only needs to catch herring in spring, remove the fish head and internal organs, clean them, put them in salt water and cook them on medium and low heat. Next, it will be canned and fermented naturally. After several months of natural fermentation, it can be put on the market for sale. Canned herring is one of the traditional Swedish cuisines. The biggest feature of this kind of food is the persistent stench. According to the relevant experimental data, the smell of canned herring is 3 times that of natto, so even if canned herring is used as food. The Swedish government also stipulates that it is not allowed to open canned herring in residential areas.