GB928452A - Improvements in the thawing of frozen fish - Google Patents

Abstract

The phenomenon of "run-away heating" in the thawing by R.F energy of deep-frozen blocks of animal matter such as fish may be avoided by determining the maximum permissible mean rate of R.F. energy input per unit mass (wmax) of a frozen block and passing blocks continuously and with minimum permissible spacing through an R.F. field at a rate (measured in terms of mass per unit time) which is calculated as the ratio of the product of wmax, the R.F. field, electrode length (l) in the direction of travel of the blocks and the width (b) and thickness (c) of a block to the enthalpy per unit mass of the block for a given input temperature; b, c and l should preferably be so chosen that all the available R.F. power (Wmax) is utilized at the electrodes, where Wmax=b.c.l.wmax Examples are given. The Specification also makes the following disclosures:- (i) each block may contain discrete units of e.g. fish of comparable size; (ii) when the blocks are conveyed horizontally between vertically-spaced upper and lower electrodes, dripping of fluid on to the lower electrode may be avoided by supporting the blocks on trays or by encasing them in waterproof containers; (iii) when a plurality of blocks are to be passed between the electrodes, arcing may be prevented by interposing thin layers of a material of high dielectric strength such as sheet polythene; (iv) for thawing fish, the electrode width should be less than that of the blocks by two inches for blocks below about twenty inches width (but of the same width for those of thirty inches width or over); (v) the R.F. energy should be fed to an electrode at its centre; (vi) an earthed screening plate may be interposed between the blocks on the conveyer and the strip connecting the upper electrode plate to the oscillator; (vii) the lower electrode should be bonded to earth; (viii) the conveyer may be supported by a lower electrode plate coated with a thin layer of polytetrafluorethylene to minimize friction.