Fermented tofu, also known as "Southern fermented food", is made from tofu as the main raw material and is fermented through a formula. The production process of Putian fermented tofu refers to the special skills of the "Hanxingji" in the Qing Dynasty, which uses a secret recipe to refine fermented tofu. The production of fermented tofu began in the Northern Wei Dynasty in the 5th century AD and gradually became a widely circulated traditional food in my country, but the production formulas and processing techniques vary from place to place. The production technique of Putian "Hanxingji" fermented tofu is special, and its history can be traced back to the Guangxu period of the Qing Dynasty. Huang Qianzhi from Ketang Village, Hanjiang, Putian, his son Huang Meilin and his nephew Huang Zhonglin opened the "Hongyuan Soy Sauce Shop" in the Xiaoyi Society of the former Hanjiang Town, specializing in the production of fermented tofu, pickles and brewed soy sauce with the secret skills of their ancestors, named "Hanxingji", and the products are very popular. Later, the brewing technology was passed on to Huang Zhonglin's four younger brothers, who set up five soy sauce companies, namely "Hongyuan", "Yuanzhen", "Yuanmei", "Jianyuan" and "Yuanchang". The business scale and product marketing volume of the five "sources" accounted for more than half of the entire industry at that time. The pickles and condiments they produced and sold were well-known in the surrounding areas, and the reputation of "pickle family" was widely spread. The raw materials of Putian fermented bean curd are mainly soybeans, rice, salt, sugar, and white wine. In the production process, old tofu is first used as the base, and molds or bacteria are inoculated on the soybean protein tissue that has been coagulated into tofu. The gel protein is decomposed to varying degrees by the protease secreted by the bacteria, generating substances such as peptones, peptides and amino acids with lower molecular weight, breaking the original structure of the protein, so the taste is relatively delicate; but the appearance still maintains its original form, and the surface is covered with mycelium. The sweetness and saltiness in fermented bean curd come from the added auxiliary materials such as sweet wine and salt, respectively. Among the decomposed substances, there are glutamic acid and some umami components generated by the autolysis of microorganisms, so it tastes delicious. In addition to the original inoculated microorganisms, some other fungi also enter the fermentation process of fermented bean curd. Due to the synergistic effect of these microorganisms, the various organic acids and alcohols produced by metabolism form various esters, forming a special aroma. "Hanxingji" preserves the complete traditional process flow with the special skills of refining fermented bean curd with ancestral secret recipes. The process is fine, the finished product has high nutritional value, and the technical requirements are strict. In particular, the ancestral secret recipe fully reflects the characteristics of color, taste, aroma, and shape in my country's traditional food culture, and has important research value.