ISO 16305|IDF 187:2005 specifies a method for the determination of the firmness of butter.

The method is also applicable to butter prepared by recombination of milk components, aerated butter, and butter to which vegetable fat, spices or other foods have been added. Any changes with regard to the preparation of the butter, however, will influence its firmness characteristics. Therefore, for the purposes of ISO 16305|IDF 187:2005 these products are not included.