GB621877A - A process for the extraction or recovery of oil and other products from herring and other fish - Google Patents

Abstract

A process for the extraction of oil and the recovery of solid products from herring and other fish containing oils and/or fats comprises the steps of heating a charge of herring in the presence of added water (preferably between 20 per cent and 40 per cent by weight of the herring) at a sufficiently low temperature, e.g. below 70 DEG C. and during the main part of the time below 50 DEG C., and during a sufficiently short period of time to avoid coagulation of any substantial part of dissolved coagulable albumens and to avoid also any extended conversion of collagen and other connective tissue substances into gelatine or glue, the temperature of the treatment depending upon the duration of the heat treatment, so as to be lower the longer the heating lasts and so that for a 30 minutes' heat treatment the temperatures are less than 60 DEG C., and for a duration of the heating of 5 minutes or less the temperature is below 95 DEG C., and thereafter treating the heated charge in a press to separate oil and aqueous liquids from solids, and drying the solids by conventional drying means, the temperature of the charge when it enters the final pressing stage preferably not exceeding 70 DEG C. The expression of oil and water from the charge of herring may take place in a continuous screw press, heating of the herring as well as addition of water thereto taking place in the inlet part of the press or in the intake chamber of the press. The pressure treatment of the charge of herring may take place in stages, water being added to the charge subsequent to one or more of the stages, and one or more of the later stages may take place at raised temperatures. The charge may be subjected to powerful mechanical working prior to the final expression of liquid therefrom. The heat required for the heat treatment may be supplied in part by means of heated herring oil or other oil brought into direct contact with the fish as a heat exchange medium. In an example fresh herring are mechanically disintegrated and continuously introduced into one end of a long trough provided with a longitudinal combined screw conveyor and agitator. The trough is enclosed in a hot water jacket and provided at the inlet end with a supply pipe for warm water. About 30 per cent by weight of water is added to the herring in the trough and the mixture of herring and water passed through the trough in about 10 to 20 minutes. The herring pulp is discharged from the trough at a temperature of about 40 DEG C. and is conveyed first to a sieve where liquid is strained off and then to a screw press for further expression of liquid. The liquid from the press and from the strainer is passed to a vessel where it is maintained at a temperature of about 60 DEG C. The surface layer of oil is skimmed off and passed to a centrifugal separator where the remaining aqueous liquid and suspended solids are removed. The press cake is disintegrated and dried in hot air. The liquid extracted from the treated herring, after having been freed from oil and from coagulable matter by heating or the addition of chemicals, may be used to supply all or part of the water required for the preparatory treatment of the next charge of herring. The coagulated albumens may be recovered by filtering them off from the aqueous liquid, and evaporating off the water remaining in the residue.