A detergent composition

A detergent composition, preferably in granular form, comprises: (i) a surfactant, preferably comprising more than 1% by weight of the composition; (ii) a system, which yields a gas on reaction, comprising: (A) an alkaline source, preferably selected from an alkali metal carbonate, an alkali metal bicarbonate, an alkali metal sesquicarbonate, an alkali metal percarbonate, an alkaline earth metal carbonate, an alkaline earth metal bicarbonate or an alkaline earth metal sesquicarbonate; (B) a dicarboxylic acid, preferably selected from fumaric acid, malic acid, maleic acid, tartaric acid or malonic acid, and the salts or esters thereof; wherein: (I) the mole ratio of (B) to (A) is from 0.005:1 to 2:1; (II) (B) has an effervescence optimum index (EOI) of not more than 4.00, wherein: EOI = MW multiplied by HI multiplied by reciprocal of (10.2 - pKa1) multiplied by reciprocal of (10.2 - pKa2) wherein: ```MW is the molecular weight of the acid source; ```HI (hydrophobicity index) represents the ratio, in the empirical formula of the dicarboxylic acid source, of the number of carbon atoms to the number of oxygen atoms; ```pKa1 and pKa2 represent the logarithm of the first, and second, dissociation constants of the dicarboxylic acid; ``` provided that: said EOI value does not take into consideration a pKa value of at least 10.2; ``` provided that: said composition does not comprise an alkali metal chloroisocyanurate.