Whey protein concentrate (WPC) has been recommended for use in emergency aid programs, but it is often stored overseas without temperature and relative humidity (RH) control, which may cause it to be rejected because of yellowing, off-flavors, or clumping. Therefore, the volatile compounds present in 14.0-kg bags of WPC34 (36% protein) and 18.7-kg bags of WPC80 (79% protein) were analyzed during storage over 18 mo in environmental chambers at 25, 30, and 35°C at RH levels of 70, 80, and 90%. An ambient chamber at around 21°C and 45–65% RH served as the control. The concentrations of dimethyl disulfide increased with time as the sulfur-containing amino acids cysteine and methionine were degraded. Five aldehydes (hexanal, heptanal, octanal, nonanal, and benzaldehyde) and 2 ketones (2-butanone and 2-heptanone) appeared as a result of lipid oxidation. Lactose breakdown led to the presence of butanol, hexanol, and furaneol. The levels of volatiles were higher in the WPC80 and tended to increase with temperature and RH. Although the color and flow properties were affected by the conditions, the generation of volatile compounds did not have a noticeable effect on product odor.