A method for the manufacture of an oil-in-water emulsion vaccine adjuvant comprising squalene, polysorbate 80 and sorbitan trioleate, the method comprising the step of: (i) formation of a first emulsion having a first average oil droplet size using a homogenizer, wherein the first emulsion is formed by circulation comprising: (a) a type I circulation of transferring the first emulsion components between a first container and a homogenizer followed by (b) a type II circulation of transferring the first emulsion components from the first container to a second container through a homogenizer, and then returning them from the second container to the first container through the same homogenizer, wherein substantially all of the emulsion components from the first container are passed through the homogenizer into the second container, and then substantially all of the emulsion components from the second container are passed through the homogenizer back into the first container; (ii) microfluidization of the first emulsion to form a second emulsion having a second average oil droplet size which is less than the first average oil droplet size, by circulating the second emulsion components through a microfluidization device a plurality of times, wherein the circulation comprises transferring the second emulsion components from a first emulsion container, through a microfluidization device to a second emulsion container, and then through the same microfluidization device. (i) formation of a first emulsion having a first average oil droplet size using a homogenizer, wherein the first emulsion is formed by circulation comprising: (a) a type I circulation of transferring the first emulsion components between a first container and a homogenizer followed by (b) a type II circulation of transferring the first emulsion components from the first container to a second container through a homogenizer, and then returning them from the second container to the first container through the same homogenizer, wherein substantially all of the emulsion components from the first container are passed through the homogenizer into the second container, and then substantially all of the emulsion components from the second container are passed through the homogenizer back into the first container; (a) a type I circulation of transferring the first emulsion components between a first container and a homogenizer followed by (b) a type II circulation of transferring the first emulsion components from the first container to a second container through a homogenizer, and then returning them from the second container to the first container through the same homogenizer, wherein substantially all of the emulsion components from the first container are passed through the homogenizer into the second container, and then substantially all of the emulsion components from the second container are passed through the homogenizer back into the first container; (ii) microfluidization of the first emulsion to form a second emulsion having a second average oil droplet size which is less than the first average oil droplet size, by circulating the second emulsion components through a microfluidization device a plurality of times, wherein the circulation comprises transferring the second emulsion components from a first emulsion container, through a microfluidization device to a second emulsion container, and then through the same microfluidization device.