For the professionals of “foie gras” production, the main quality criteria of this product are the liver weight and the technological yield after cooking (TYC). Contrary to the liver weight that is easily known after the duck evisceration, the TYC is only known after cooking the livers by pasteurization or sterilization. However, the TYC depends on the liver weight and on the cooking process and strongly impacts the valorization of the products. Thus, the study aims to identify biomarkers correlated to the TYC and that could predict the TYC before cooking the livers. A group of 120 male mule ducks were overfed during 12 days (twice a day). A subgroup of 30 ducks were slaughtered at day 6, day 8, day 10 and day 12. Their liver was taken off. For each liver a slice of 180 g was sampled and cooked by pasteurization in a glass jar to determine the TYC, and a sample of 20 g was frozen. One hour before the slaughtering, blood was collected at the occipital sinus and the plasma was extracted and frozen. Nuclear Magnetic Resonance of the proton (1H-NMR) analyses were performed on the plasma samples and on the hydrophilic extracts of the liver. A total of 15 plasmatic biomarkers and 13 hepatic biomarkers of the TYC were identified that are mainly amino acids and carbohydrates. These biomarkers could help to predict the TYC of the “foie gras”. Thus, they could be very useful for the “foie gras” producers. The utilization of these biomarkers might be helpful for optimizing the “foie gras” process, for the duck selection and for improving the feed additives in duck nutrition to reduce the melting rate at cooking of “foie gras”.