Grading And Cleaning Potatoes

Press, Volume XCVIII, Issue 28938, 4 July 1959, Page 9

Grading And Cleaning Potatoes

The handling of the main potato crop in Canterbury is concentrated in only a few months of the year and at a time when unfavourable weather and holdups can cause heavy losses to the grower. Merchants who handle potatoes for the North Island market find a serious bottleneck occurs in stores after the grower’s line has been accepted and has to be graded before shipping. Once a line of potatoes has been graded it can be bulked with other lines of comparable quality but ungraded lines take up considerably more room in the store. The factor governing the efficiency of the store is the grading unit. Two of the largest grading and dry-cleaning units in New Zealand, which will handle up to 700 sacks a day with an 11-man team, have been designed and built by * Skillings Implements, Ltd., a Christchurch agricultural engineering firm which has manufactured equipment for the potato industry for many years. One machine was put into use during last season and the second was installed recently. The principle employed is the sizing of the potatoes by shaped

rubber rollers set at determined spacings to allow definite sizes of tubers to pass through. The rollers are covered with small teats, or projections, which have a scrubbing action on the dirt without damaging the skin of the potato. The speed of the rollers is sufficient to give a rolling action as the potatoes pass along but is not enough to make them tumble, which would cause bruising. The sacks from the grower are emptied into a hopper and the potatoes pass up an open conveyer through wich the loose dirt and remaining haulms fall. The first section of the rubber rollers takes out the pig potatoes and the next the one to two-ounce seed. From there a further section sorts out the two to four-ounce seed, and if necessary a further grading of four to six-ounce potatoes can be taken.

The larger potatoes then move on over a further set of rubbers to complete the cleaning and at this stage are inspected for faults. The seed sizes also pass along inspection conveyers before they reach the bagging platforms. The capacity of the unit is governed by the amount of earth

included in the grower’s line, the ratio of seed to table, in the sample and the amount of damage or any other fault. An illustration of the amount of dirt which can be brought into store is the amount extracted from one line graded this season on the machine owned by Field and Royds at their Hornby store. A line of 1485 sacks received from one grower contained just under 10 tons of dirt, or about 10 per cent. This was the equivalent to between 15 and 161 b of dirt a sack.