Reverse osmosis (RO) and ultrafiltration (UF) retentates were ultra-high temperature (UHT) processed and compared for storage life at room temperature. Viscosity studies indicated that UHT-treated, RO retentate delayed age gelation longer than UF retentate at the same total solids level (26% TS). When compared at 6.4% protein level (2x RO vs 2.7x UF where x=ratio of the feed volume to concentrate volume), the storage life for both RO and UF retentates was about 6 to 8 months. Sodium hexametaphosphate (SHMP) and disodium phosphate (DSP) at 1, 3, 5, 10, and 20 mM concentrations were incorporated prior to UHT processing of each sample to improve the shelf life. SHMP at 1 and 3 mM concentrations was effective in delaying age gelation, whereas all levels of DSP accelerated gelation. However, SHMP accelerated age gelation at concentrations of 10 and 20 mM. SHMP at 1 mM in RO retentate was more effective in delaying age gelation than the same SHMP level in two UF samples (22 and 26% TS). Analysis showed that RO/UHT-treated samples had higher soluble calcium and ionic calcium than did UF/UHT-treated samples. The coefficient of determination (R2) was .80 between soluble calcium-to-protein ratio and shelf life.