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The influence of ethanol (0–10%, <i>v/v</i>) on the acid-induced flocculation of casein micelles was examined using diffusing wave spectroscopy. For this purpose, samples containing 10% (<i>w/w</i>) reconstituted skim milk powder and 0–10% (<i>v/v</i>) ethanol were acidified with glucono-delta-lactone and acid-induced coagulation was monitored by diffusing wave spectroscopy. The pH at which acid-induced flocculation of the casein micelles commenced (pH_f) increased near-linearly with increasing ethanol content, whereas the rate of flocculation was not affected by ethanol. The results are discussed in terms of the steric stabilisation of casein micelles by a polyelectrolyte brush in a medium of high ionic strength. Ethanol-induced increases in pH_f are probably primarily due to an ethanol-induced reduction in solvent quality; an ethanol-induced reduction in dissociation of carboxylic acid groups in the brush is likely to contribute.