This paper aims to fully demonstrate the feasibility of the use of the bottle-in-bottle structure for food contact purpose, and provide convenience for the majority of peer practitioners. Firstly the principle of the second-generation''bottle-in-a-bottle'' is introduced where the alcohol concentration can be adjusted automatically, and the hidden food hygiene and safety hazards in the assembly process are analyzed. The inner and outer bottles are connected and rotated together to avoid direct contact between them, and then a specially designed tooling is used to press-fit the closure to realize the isolation of the inner and outer bottles, finally the inner and outer bottles are cleaned separately. Different bottling lines can bottle the inner bottle and the outer bottle separately. All these measures are taken to solve the hidden hazards in both the safety and hygiene one by one. After the second-generation bottle-in-a-bottle is assembled, it can meet the alcohol concentration automatic adjustment accuracy and the national food hygiene and safety requirements. The second-generation "bottle-in-bottle" structure can allow free adjusting of liquor with alcohol concentration of 38%, 42%, 45%, 52%, and 69%. The filling method introduced in this article can ensure food hygiene and safety, and achieve high-efficiency mass production, which can be used as a reference for the same type of packaging.