a side view of an embodiment of the vane type impeller built in accordance with the present invention partly broken away for illustration fig3 is a side view of another embodiment partly broken away for illustration fig7 is a partially broken away perspective view of another embodiment and fig8 is a schematic cross section of a fermentor equipped with the impellers of one embodiment indicating the mode of arrangement of the impellers in the fermentor the identical or related reference numerals are used to indicate the corresponding parts or components of the exemplified impellers as well as an apparatus equipped with the impeller throughout several views in each of the figures numeral 1 indicates inclusively an impeller which has a center hub 2 vane s or blade s 3 radially planted on the hub 2 and a grating 5 composed of a plurality of closed loops of strand 4 encompassing the outer periphery of the body of revolution defined by the vane s the grating 5 is usually secured to distal s 3 39 of the blade s by rivetting or welding though it may alternatively be supported by independent stems not shown planted directly on the hub 2 in the embodiments of fig3 and 6 the strand 4 is wound spirally around the impeller 1 to form the grating 5 a side loop 4 39 is also provided on the front face of the impeller 1 of the former embodiments only part of the strand 4 wound around a single spiral vane 3 is shown in fig6.