It melts less and tastes better when it is cooked immediately after the geese are slaughtered.
BOTH ALSACE AND THE SOUTHWESTERN REGION of France claim to have been the first to invent foie gras, but it is not a new delicacy: The Romans are known to have force-fed geese with figs. The manner in which it is prepared is changing, however. Goose livers traditionally were cooked several hours after the animals had been slaughtered, but a revision of food industry regulations in France has led to a centralization of local slaughterhouses and, with it, the practice of immediate evisceration and cooking. What effect has this had on the quality of the livers?
In the early 1990s, a team headed by Dominique Rousselot-Paillet and Gérard Guy at the Institut National de la Recherche Agronomique (INRA) station in Artiguères succeeded in showing that livers obtained by on-the-spot (à chaud) evisceration lost less fat than ones that had been allowed to cool down before cooking. Producers were delighted, but they worried that the new method would have adverse consequences from the point of view of taste. To resolve the matter, which concerns one of the glories of French cuisine, Sylvie Rousset-Akrim and her colleagues at the INRA station in Clermont-Ferrand analyzed the sensory characteristics of canned foie gras prepared under both conditions.
Thirty geese were raised and force-fed at Artiguères. After immediate evisceration the large lobe of the livers was cut lengthwise into two parts. One sample was sterilized at once at 105°C (221°F) for 50 minutes, and a second sample, taken from the other half of the lobe, was prepared following the same procedure, only à froid, which is to say after several hours of cold storage. Then the two samples were tested by trained tasters.
Earlier studies comparing goose and duck foie gras revealed a great disparity between livers and helped researchers develop the protocol for later tests. The tasters were instructed to grade the intensity of eighteen aspects of the cooked livers on a scale of 0 to 20: appearance (compact, smooth, veined), odor (chicken liver, foie gras), texture (sticky, compact, firm, tender, granular, plump, smooth, crumbly), taste (sour, bitter), and aroma (defined as a detectable part of flavor: foie gras, chicken liver, rancid). Statistical analysis of the results yielded the desired information.
First, the Clermont-Ferrand team showed that human beings are reliable measuring instruments when one knows how to use them. In many cases it was possible to distinguish the two modes of preparation. In particular, the livers that had been cooked at once were both more veined and more tender, plumper and smoother, less granular, less friable, and less bitter, with a foie gras aroma that was more developed than that of livers prepared after a few hours’ delay. The sticky livers were the plumpest and the least crumbly. The compact livers were the firmest and smoothest and, again, resisted crumbling. Finally, the most granular ones were the most friable and also the least plump and smooth.
More Tender, More Fragrant
Similarly, the statistical analysis showed a correspondence between odors and aromas, the aromas of chicken liver and rancidity being opposed to the aroma of foie gras. Acidity varied inversely with the intensity of the aroma of foie gras. But to a greater degree than either odor or taste, the various aspects of texture were positively correlated with aroma: In addition to smoothness of appearance and the odor of foie gras, tenderness, compactness, plumpness, and smoothness were associated with the aroma of foie gras.
Without making any prior assumptions, the tasting distinguished two groups. The first consists mainly of livers prepared à froid, which have a granular, friable texture and an aroma of chicken liver with a note of rancidity; the second group is composed of livers prepared à chaud (along with a few livers from the first group), which are plumper, more tender, and smoother.
What accounts for this division? The fact that the lipid melting rate (the rate at which fatty matter is released during cooking) is far higher for livers prepared à froid (21%) than for ones prepared à chaud (9%) suggests that rapid removal and cooking of the liver after slaughter prevents the postmortem change of hepatic tissue, limiting membranous lesions and the escape of lipids.
The melting rate depends on the mass of the livers in the case of preparation à froid but not in the case of preparation à chaud. And no matter which mode of preparation is used, warm or cold, compactness and firmness vary inversely with the weight of the liver: The heaviest ones were found to be less compact and less firm. But when the melting rate increases, as in the case for the livers prepared à froid, the foie gras seemed more granular, friable, rancid, and also less smooth, tender, compact, plump, and aromatic.
Producers have no reason to worry, because the new method of cooking livers immediately after the geese have been slaughtered does not harm their product—quite the opposite. Cooks will draw the same conclusion: The best foie gras is made from livers obtained directly from the slaughterhouse.