Producers of nonfat chocolate milk have reported shelf-life failures of a musty off odor. The objective of this study was to determine when the failure takes place in shelf-life. Nonfat chocolate milk products with and without off-odors were acquired from regional processors. A shelf-life study was performed to detect when the musty off odor occurs. Fresh product was stored at 7°C and evaluated daily for the presence of the odor. It was determined that product failure occurred between d 15 and 17 with 100% product failure. Microbiological analyses were performed using standard serial dilution and spread-plating methods on tryptic soy agar for standard plate count (SPC), pseudomonas isolation agar (PIA), spirit blue agar (SBA), skim milk agar (SMA), MRS Agar, eosin methylene blue (EMB) and MacConkey, and chocolate milk agar. Chocolate milk agar was prepared using 2 formulations: one agar was prepared by adding chocolate milk to standard methods agar, while the other was prepared by adding chocolate syrup to skim milk agar. These media were selected to help differentiate the colonies that grow in a chocolate environment. All plates were incubated at 25°C before enumeration. The chocolate milk samples analyzed at 6 d had counts of <10 cfu/mL on all media types. At 15 d the samples had a SPC of 10⁴ to 10⁶cfu/mL. Coliforms and lactic acid bacteria were <10 cfu/mL for all samples. Bacteria producing proteolytic and lipolytic enzymes were detected on SMA and SBA in all samples. The 2 chocolate milk agars performed equally well, and had growth of similar morphology from all samples. A musty odor was observed during incubation on the chocolate milk agars, and it increased with growth. This indicates that chocolate milk agars may be effective as early warning for product failure.