A lactone is a cyclic ester in organic chemistry . It is the conensation product of an alcohol group and a carboxylic acid group in the same molecule. The most stable structure for lactones are the 5-membered lactones (gamma-lactone) and 6-membered lactones (delta-lactone), because of the minimal angle strain in the compounds' structure. Gamma-lactones are so stable that, in the presence of dilute acids at room temperature, 4-hydroxy acids (R-CH(OH)-(CH2)2-COOH) immediately undergo spontaneous esterification and cyclisation to the lactone. Beta-lactones do exist, but can only be made by special methods.