Cryogenic freezing of food materials as preparation for crushing
Special Symposium - Innovations in Food Technology (LMC Congress)
Process & Product Innovation (Food-4b)
Keywords: Cryogenic freezing, spices, berries, time of freezing
Cryogenic freezing of food materials is carried out at direct contact of cryogenic liquids to a processable material. The given process is developed in connection with crushing of such food materials as berries or spices with reception of food powders. The basic purpose of cryogenic freezing - reception of necessary properties of particles of a material for the subsequent mechanical crushing with achievement of reduction of the sizes of particles without heating with reception of a high quality product with preservation of aromatic qualities and colors.
Spices and berries contain various oils, including a valuable flying component that results in difficulties at their crushing. Growth of temperature during crushing conducts to losses of flying aromatic components that are not only valuable, but also dangerous, for example such component as capsaicin of pepper red. Developed during crushing heat, usually is harmful to a product and results in some deterioration of taste and quality. Oils in structure of spices interfere with destruction of particles at crushing.
During crushing the temperature of a product raises up to a level from 42 °С up to 95 °С which vary depending on the contents of oil and a moisture in spices, and, owing to such growth of temperature, spices lose a significant part of the flying oil and aromatic substances. In different spices such losses achieve 37 % at crushing a nutmeg, 32 % - in seeds of caraway seeds, 14 % - in a dried peel of a nutmeg and 17 % - in cinnamon.
Losses of flying oil can be appreciably reduced by the method of cryogenic crushing. Liquid nitrogen at temperature -195,6 °С provides the temperature necessary for preliminary cooling of spices, achievements of transition of oils into a firm fragile condition and maintenance required of low temperature a level due to absorption developed during crushing heat. Besides maintenance of low temperature a level, evaporation of liquid nitrogen up to a gaseous condition actually creates an inert and dry atmosphere for additional protection of quality of a product. Preliminary cooling of spices and low temperature constantly supported in a grinder reduces a level of losses of flying oils and a moisture, thus keeping the most part of the aromatic substances.
Theoretical researches of process of cryogenic freezing have allowed to develop a method of calculation of time of process of freezing of the particles having the wrong form. Also calculations of fields of temperature in frozen materials that is necessary by optimization of modes of process of cryogenic freezing are executed.
Process is developed and the device for cryogenic crushing with cooling spices before their submission in a grinder and also with maintenance of low temperature in a zone of crushing is designed. Basic elements of such device are the preliminary cooler and a grinder. The device of preliminary cooling will consist from the screw conveyor with a drive, and also Dewar vacuum vessel with liquid nitrogen. To submit of liquid nitrogen in process able spices in a preliminary cooler the compressor that a forcing of air supersedes liquid nitrogen from Dewar vacuum vessel on the pipeline to the allocator on the screw conveyor is used.
Presented Thursday 20, 10:05 to 10:10, in session Process & Product Innovation (Food-4b).
