Melatonin is synthesised by yeast during alcoholic fermentation in wines

► Melatonin is a new bioactive identified by LC-MS/MS in six monovarietal wines. ► Melatonin was not detected in skin, seeds or pulp in 13 grape varieties analysed. ► Melatonin was not found in the musts but it is formed after yeast addition. ► Melatonin concentrations range from 245.46 ng/ml (Merlot) to 423.01 ng/ml (Syrah). ► The white wine value is within this range (Palomino Fino 390.82 ± 10.05 ng/ml).