Fluid milk may be pasteurized by high-temperature short-time pasteurization (HTST) or ultrapasteurization (UP). Literature suggests that UP increases milk astringency, but definitive studies have not demonstrated this effect. Thus, the objective of this study was to determine the impacts of pasteurization method, storage time, and fat content on milk sensory and mechanical behaviors. Raw skim (<0.5% fat), 2% fat, and 5% fat milks were pasteurized in duplicate by indirect UP (140°C, 2.3 s) or by HTST pasteurization (78°C, 15 s), homogenized at 20.7 MPa, and stored at 4°C for 8 weeks. Sensory properties, instrumental viscosity, and friction profiles were evaluated at 25°C at 1, 4, and 8 weeks. SDS-PAGE and confocal microscopy were used to determine protein structural changes in milk at these time points. Fresh milks were processed by HTST at wk 7 for wk 8 evaluations. UP increased milk sensory and instrumental viscosity compared with HTST pasteurization (P < 0.05). Increased fat content increased sensory and instrumental viscosity, but decreased astringency and friction profiles (P < 0.05). Astringency increased for UP versus HTST (P < 0.05); however, UP did not significantly affect friction profiles (P > 0.05). Increased storage time increased instrumental viscosity and friction profiles (P < 0.05) but did not affect sensory viscosity or astringency (P > 0.05). SDS-PAGE and confocal microscopy showed more denatured whey proteins in UP processed milks compared with HTST processed milks. The network formed by these proteins likely caused the increase in viscosity during storage. Astringency and increased friction were likely due to the presence of denatured proteins, which formed large molecules. Overall, fat content had a greater impact on milk mechanical and sensory behaviors than storage time or heat treatment. Mechanical–sensory relationships were not straightforward; however, instrumental testing may still be used to evaluate milk behavior and enhance the understanding of sensory behaviors.