Custard cream-based desserts, made up of highly nutritive raw materials, are easily spoiled by specific microbial contaminants. Little is known about these spoilage issues. The objective of this study was to fully characterize the type of bacteria and the respective metabolic activities involved in the spoilage of custard cream-based desserts. Materials &Methods (700) The level of bacterial contamination of 64 spoiled commercial custard cream-based desserts was measured (PCA, 24h, 30°C) and colonies were identified based on their 16SrDNA sequences. Over a bacterial collection of 565 isolates, 33 isolates of the 4 dominant genera were submitted to individual challenge tests (inoculum size of 3 log CFU/mL, incubation at 10°C for 21d in sterile custard cream). Microbial growth, sensorial evaluation, and biochemical changes (acidification; hydrolysis of sugar, protein and fats; production of volatile compounds and organic acids) were measured and the set of data was subjected to a principal component analysis (R software). Results (360) The spoilage was characterised by high bacterial counts (> 6 log CFU/mL) with predominance of Gram-positive bacteria, including Bacillus cereus group cells. The metabolic activities were highly dependent on the genus. The volatilome fingerprint appeared as a specific marker allowing assigning each type of spoilage to a specific bacterial genus. Significance (125) A better understanding of custard cream spoilage issues could help manufacturers improve detection and prevention.