Stability of carotenoids is a key for successful product form development and of particular interest in synthesis and adjacent crystallization as well as in formulation processes. Ethyl acetate was used as model solvent to demonstrate decomposition of astaxanthin due to the presence of traces of acetic acid and oxygen. Based on solvent pretreatments, i.e., by means of oxygen stripping, the stability could be enhanced significantly. Additionally, the stability was improved with regard to the desired isomeric configuration. Deceleration of the carotenoid isomerization by potassium carbonate was demonstrated in dichloromethane. In the case of corn oil, the degradation was negligible under ambient conditions, while decomposition occurred at higher temperatures. Presence and quantity of peroxides proved to be indicators for oil quality and associated degradation kinetics.