Sugar and an electrical field can be used to accelerate smoking.
SMOKED SALMON IS AN EXPENSIVE DELICACY that France has long specialized in producing. Manufacturers buy imported salmon and resell their smoked filets the world over. A team of researchers from the Institut Français de Recherche pour l’Exploration de la Mer and the Centre de Coopération Internationale en Recherche Agronomique pour le Développement perfected the process currently used to accelerate processing without sacrificing flavor. The two principal ingredients of the new method are osmosis and electrostatic smoking.
Smoking, like salting and drying, was originally used to preserve foods. In all three cases the idea was to eliminate water from foods in order to kill microorganisms that were already present and to prevent the development of new pathogenic microorganisms. Yet the old methods often gave an excessively salty or smoky flavor.
With the appearance of modern refrigeration systems, the technique of smoking was retained, in a modified form, because it gave filets of fish (and other foods) the delicious taste we know and love. Present-day products are less salty and less smoky, but they must be kept at low temperatures, between O°C (32°F) and 2°C (36°F).
Fish filets prepared by traditional methods are either immersed in a brine, sprinkled with salt, or injected with brine. The first treatment, which takes about four hours, eliminates only about 2% of the water; health regulations make it a complicated affair requiring costly treatment facilities. The elimination of water is ensured only by drying at a temperature of about 22°C (72°F), with a humidity of 65%, for three to four hours, before the actual smoking begins. Here again the procedure must be carefully monitored, for the processing temperatures favor the development of microorganisms.
In the procedure patented by Antoine Collignan, Camille Knockaert, Anne-Lucie Wack, and Jean-Luc Vallet, the salting and drying are done simultaneously at a temperature of 2°C (36°F). The filets are immersed in a concentrated salt and sugar solution (10–30% sugar and 70–90% salt) so that some of the salt penetrates the flesh by osmosis and dries it out. In fact, the various molecules are distributed in such a way that their concentration is everywhere the same: When the filets are immersed in a salt-saturated solution, the salt migrates toward the flesh and the water comes out. At the same time the sugar—composed of large molecules that cannot enter the cells of the fish—promotes the outflow of water as well. All told, filets immersed in a solution containing some 350 grams of salt per liter and about 1900 grams of sugar per liter lose roughly 10% of their water. Moreover, the sugar reacts with the amino acids of the fish and produces agreeable flavors through a series of Maillard reactions. In certain classic recipes for smoked salmon the fish is rubbed with sugar until it has a tanned appearance. With the new procedure, the result is comparable but easier to achieve because it takes place in solution.
Smoke Without Fire
After rapid rinsing and draining, the smoking takes place in a chamber traversed by a metal conveyor belt that passes under a grate. Smoke is produced by subjecting sawdust to pyrolysis (dry heat). The smoke is injected into the chamber after having been cooled to a temperature of 40°C (104°F), condensing the aromatic polycyclic hydrocarbon molecules, which are carcinogenic, so that they do not contaminate the filets. After being electrically charged as they pass under the grate, the smoke particles are impressed on the filets by a difference in electrical potential (amounting to several tens of thousands of volts) between the conveyor belt and the grate. In this method the smoking lasts fifteen minutes (rather than three and a half hours, as in the usual procedure) so no additional drying out occurs.
The electrical system could easily be adapted to the scale of traditional smoking, where up to 400 kilograms (880 pounds) of salmon filets can be treated at a time, and the new method of salt drying and cold smoking could be applied to various other meats and fish. Naturally, one wants to know whether products prepared in this way are as good as the old ones. At first their coloring was a bit more pronounced than that of smoked filets today, but by prefiltering the smoke it became possible to give them a lighter tint. As for the flavor, it is not noticeably different from that of salmon smoked in the traditional manner.