ISO 19662 | IDF 238:2018 specifies a method, the acido-butyrometric or "Gerber", for determining the fat content of milk. It is applicable to whole milk and partially skimmed milk.
It is also applicable to milk containing authorized preservatives (potassium dichromate, bronopol).
It does not apply to formalin milk, nor to milks that have undergone a homogenisation treatment.