Archive Article: 1997/08/02

2 August 1997




TUBER damage could be halved on many farms if operators made full use of all the adjustments available on todays harvesters.

That fact, however, is constantly ignored, according to research by the Sutton Bridge Experimental Unit (SBEU).

Pinpointing which part of your harvesting operation is causing the damage is the key to solving any potential damage or bruising in harvesting and grading operations.

Many resort to the electronic potato but there is a less hi-tech method that the SBEU carries out on behalf of growers every year. Devised at the Scottish Centre for Agricultural Engineering in 1970, it uses the following visual classification to calculate a potato damage index:

&#8226 undamaged

&#8226 scuffed (skin only broken)

&#8226 slight (flesh damage removable by two strokes of a peeler)

&#8226 severely damaged (flesh damage not removable by two strokes of a peeler)

SBEUs Patricia Harbour explains how it works: "We use a 10kg sample of potatoes. Each tuber is by hand and then individually assessed into one of the above categories. The weight of each category is recorded as a percentage of the whole 10kg sample."

A damage index is then calculated by taking the percentage weight of scuffed tubers. This figure is added to three times the percentage weight of slightly damaged tubers and, then added to seven times the percentage weight of severely damaged tubers. The multiplication factors reflect the importance of each type of damage.

The net result? Less than 50 is not worth worrying about, she says. But a damage index of more than 50 requires a rethink on the harvesting operation; more than 100 is a big problem.

An index for bruising is also used. It is carried out along similar lines, but the bruising in the tubers is accelerated by placing them into a hotbox so that visual assessments can be made.

However this system does have some disadvantages, according to Ms Harbour. "A wound of any depth receives the same weighting regardless of its length."

It is also reliant upon weighing, which can mean delays during harvesting while samples are sent back to the farm.

A new method, funded by the British Potato Council, is therefore being assessed. It involves counting the number of strokes, made with a stirrup-type potato peeler, needed to remove all damaged tissue from a given number of tubers.

So the range and spread of damage is discerned simply by the number of peels removed. Then the number of tubers in each category is counted.

However, although the new system compared well against the old damage index there are two drawbacks: "It takes longer to perform, despite there being no need to weigh the potatoes. And there is no assurance that damage scores made by different assessors using the new system would be consistent," explains Ms Harbour.

So it is back to the old damage index system for the moment, until the new one can give reliable results.

How much damage is your harvesting setup doing? Scientists are continuing their

quest to find answers.


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