Altering the casein:whey protein ratio (CN:WP) is an important determinant of the quality of yoghurt. In this study, the textural, rheological, microstructural and volatile aroma compound release properties of non-fat stirred yoghurts with varying CN:WP were compared. Yoghurts were manufactured using different fortifiers (whey protein isolate, sodium caseinate, low-heat skim milk powder) to achieve varying CN:WP at total protein levels of 4, 4.5 and 5%. At all protein levels, yoghurts with lower CN:WP were firmer and stiffer than those with higher CN:WP. Yield stress of gels increased when the CN:WP deviated from the unfortified CN:WP, 3.2:1. Samples with low CN:WP also had a more elastic gel at 4.5 and 5% total protein. Alteration of CN:WP did not significantly alter volatile aroma compound release from yoghurts. The results demonstrate that CN:WP, and not only total protein or total solids, is an essential consideration when formulating non-fat stirred yoghurts with acceptable qualities.