They’re best cooked slowly after the dough has been chilled and allowed to rest.
AS WITH ÉCHAUDÉS, often called gnocchi today, there are many recipes for fish quenelles, but whether they call for salmon or trout or pike they are all variations on a theme: To the finely ground flesh of the fish one adds fat (beef kidneys, butter, or cream) and perhaps egg and panada (either bread soaked in milk or a dough made by combining flour with boiling water). The ingredients are kneaded for a long time—so long, in fact, that Isabella Beeton (author of the famous cookbook published in England in 1860 as Beeton’s Book of Household Management) wrote, “French quenelles are the best in the world, because they swell up more.” And they swell up more, she explained, because they are kneaded longer.
Why should kneading quenelles have anything to do with their succulence? And why should quenelles hold their shape during cooking, even when they do not contain any egg? Florence Lefèvre and Benoit Fauconneau at the Institut National de la Recherche Agronomique (INRA) in Rennes have indirectly answered the question by exploring the thermogelling properties of river (or brown) trout.
The fleshy tissue of the trout is composed of cells, or muscle fibers, that contain myofibrillary proteins. These proteins, which are responsible for muscle contraction, form a gel when they are heated in a water solution. Like the proteins in egg whites, the proteins in trout muscle tissue bind together, creating a network that traps water. In a quenelle, this gel also traps fat and the expanded starch granules contributed by the panada.
Understanding the chemistry of gelatinization allows us to make quenelles and various other products from farm-raised salmon. These products, which Norwegian companies hope to bring to market soon, would be culinary cousins to Asian fish noodles and surimis (dumplings made from freshwater fish such as carp, especially in China). In France, where farm-raised trout is more common, the proteins of this fish are being studied with a view to creating new products as well.
Which proteins form these gels? Like all cells, muscle fibers contain sarcoplasmic proteins that regulate cellular function and maintenance. But they also contain specific myofibrillary proteins, of which the main ones are actin and myosin. In water solution, Lefèvre showed, only the myosin gels alone. The actin by itself does not gel, although incorporating it in a myosin preparation was found to increase the rigidity of the gel.
Under what conditions does gelatinization take place? In the case of quenelles, as in other dishes that depend for their effect on myofibrillary protein gels, the practical problem is how to combine the greatest possible tenderness with sufficient firmness. The parameters that determine the firmness of a gel are the storage time of the solution, the rate of heating, and the maximum cooking temperature, in addition to the protein concentration, acidity, and salt concentration of the solution.
To study the effect of these factors, the biochemists in Rennes inserted the pointed tip of a penetrometer into the trout with constant pressure and measured the degree of deformation. Having first established that this test gauges firmness in the same way biting into the flesh of a fish does, the researchers went on to analyze the gels formed by heating different protein solutions and discovered that the maximum protein concentration was on the order of 10 grams per liter.
A Well-Deserved Rest
Firmness depends also on the length of time solutions are stored, for it is during this time that protein interactions begin to form a gel. Its firmness changes during cooking. A few minutes’ heating within a range of 70–80°C (158–176°F) is enough to stabilize the incipient gel, but prolonged cooking re sults in a loss of water and therefore of tenderness. A rate of heating of 0.25°C per minute has been found to produce a sufficiently firm and elastic gel for making quenelles.
Because proteins contain ionizable lateral groups, their behavior depends especially on the acidity of the solution in which they are placed: In an acidic environment, the acid groups of the proteins are unchanged, but the base groups bond with a hydrogen ion, positively charging the protein molecules and causing them to repel one another rather than to combine. Conversely, in an insufficiently acidic environment, the base groups are neutralized while the acid groups are ionized, likewise producing a repulsion. Thus the acidity of the solution determines the bonds not only between proteins but also with water molecules. The optimal acidity levels depend on the proteins involved and on the animal species from which these proteins come. The INRA chemists showed that, in the case of river trout, the formation of gels is optimized when the acidity of the protein solution is higher (a pH of about 5.6) than the levels conducive to gelatinization in other fish.
This research makes it possible, finally, to perfect the classic preparation of quenelles. First, the quenelle dough must be chilled and left to rest for a few hours, so that a gel forms from the proteins released by the ground muscle fibers. The quenelles themselves should then be heated gently, in a very low oven. Finally, if the quenelles have been slightly acidified, the firmness this imparts will yield a more tender result through the addition of extra water (which in this case means a strongly flavored liquid such as shellfish fumet or fish stock) during cooking.