Provided is a quick and accurate way of assessing harshness of a surfactant towards a protein, which can be easily carried out under non-laboratory conditions and which facilitates recommendations for making suitable products. Particularly, provided are methods of measuring the harshness of a surfactant, which includes (a) providing an aqueous solution of surfactant and taking a first colour measurement; (b) adding a solid protein-dye complex to the aqueous solution of surfactant; (c) taking a second colour measurement and measuring the change in colour between the first colour measurement and the second colour measurement; and (d) matching the change in colour with a reference scale. The solid protein-dye complex can be prepared by dissolving a non-denatured corn protein and a protein binding dye in aqueous alcohol, and removing the aqueous alcohol.

A method of measuring the harshness of a surfactant, comprising the steps of: i) preparing a solid protein-dye complex comprising: a) a protein, which is a non-denatured corn protein and which is soluble in aqueous alcohol; and b) a protein binding dye, which is specific to the protein (a); by dissolving a) and b) in aqueous alcohol to form a solution of protein-dye complex; and removing the aqueous alcohol to form a solid protein-dye complex; and ii) providing an aqueous solution of surfactant and taking a first colour measurement, iii) adding the solid protein-dye complex to the aqueous solution of surfactant, taking a second colour measurement and measuring the change in colour between the first colour measurement and the second colour measurement; and iv) matching the change in colour with a reference scale; provides a quick and accurate way of assessing surfactant harshness towards protein, that can be easily carried out under non-laboratory conditions and enables suitable product recommendations to be made.