Method of making expanded foodstuffs
This application is a continuation of application Ser. No. 07/274,059 filed as PCT/EP88/00286, Apr. 7, 1988, now abandoned. 
    
    
     The invention relates to a method of making expanded foodstuffs, a dough emerging from the nozzle of an extruder and the extrudate being subjected to an after-treatment in a hot medium. 
     Essentially two methods are known for the extrusion technique production of expanded foodstuffs, so-called snacks. 
     In the so-called direct expansion the dough is processed at high temperatures and pressures and expands into its final form on emergence from the nozzle of the extruder. 
     In the so-called indirect expansion the dough is pressed at lower temperature and lower pressure through the nozzle of an extruder. The dough becomes pasty in the extruder. The resulting product is similar to pasta. In a subsequent complicated drying process lasting 4 to 8 hours the moisture of the extrudate is reduced to about 11% and after a further conditioning time the extrudate is either placed in hot fat or in hot air for the expansion. 
     In the extrusion method with direct expansion usually extrusion moisture contents of 13% to 22% are employed whilst in the extrusion with indirect expansion the moisture content of the raw material is about 28% to 40%. The reduction to a moisture content of about 11% takes place in a drying process, as mentioned above. 
     Furthermore, various methods of making expanded foodstuffs are known which combine the extrusion with direct expansion with an after-treatment in hot fat. The extrudate is baked in hot fat after emerging from the nozzle and cutting. On emergence from the nozzle the extrudate is subjected to a cooling by the expansion taking place and water evaporation. The after-treatment in hot fat thus has primarily a drying and roasting character and a volume or texture change of the foodstuff is not achieved. 
     The advantage of extrusion with indirect expansion over the method employing dried semiproducts (as a rule in the form of pellets) is that very specific flavour and texture results of the foodstuff can be achieved which in their quality are higher than those of directly expanded extrudates. The disadvantage of the production method with indirect expansion is however that such an apparatus for making the semiproducts and drying thereof is very complicated and expensive. In addition, a quality control and obtaining constant quality is very complicated and obtainable only with great difficulty. Furthermore, the energy consumption for the manufacturing is very high when using this method. 
     The invention is based on the problem of providing a method which gives foodstuffs with taste and texture properties which correspond to those of foodstuffs made with a method with indirect expansion but avoids the disadvantages of the latter method, in particular the high costs and the difficult quality control. 
     This problem is solved according to the invention in that the extrudate is kept after emergence from the nozzle at a temperature which corresponds substantially to the emergence temperature of the dough and that the after-treatment takes place directly after the extruding. 
     According to the invention the extrudate is subjected directly to a strong heat treatment in hot oil, hot air or hot steam without intermediate cooling at higher temperatures (105° to 130° C.) than in the known method. The heat withdrawn from the extrudate by evaporation of water in the expansion after emergence from the nozzle does not result in an otherwise usual hornification of the dough and termination of the expansion but instead due to the heat carrier into which the extrudate is conducted a considerable amount of heat is supplied, the viscosity of the dough thereby being reduced and a considerably greater expansion effected. The resulting texture, in particular the crispiness and the chewing feeling of the extruded foodstuff, is identical to the product otherwise produceable only by extrusion with indirect expansion. Consequently, with the method according to the invention foodstuffs of high quality are obtained and complicated apparatuses for drying and conditioning semifinished products can be dispensed with. Whereas a conventional apparatus for making pellets and carrying out the necessary process steps costs about DM 2 million, a plant for carrying out the method according to the invention costs less than half this sum. Since a tedious drying of semi-finished products is dispensed with the quality control and the quality constancy of extruded and expanded foodstuffs is simpler. In addition the energy consumption is greatly reduced with the method according to the invention. 
     According to a preferred embodiment the dough is extruded from the extruder directly into hot oil or fat. The nozzle of the extruder is preferably disposed in the hot fat or oil. 
     According to a further preferred embodiment the extrudate is conducted through a passage in which a temperature and a moisture content obtain which are equal to the temperature and the moisture content of the extrudate so that neither a heat nor a moisture loss of the extrudate occurs before the latter is introduced for example into hot oil or fat. In the passage through which the extrudate is conducted preferably vapours of the medium in which the after-treatment of the extrudate takes place are contained. The medium for the after-treatment of the extrudate may be hot fat, oil, hot air or hot steam. It is for example possible to conduct hot air to the nozzle with a temperature of for example 600° C.