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Putting the finger on thumbnail damage

30 August 2011

A revolutionary new store-warming system is helping Lincs-based suppliers Manor Fresh put an end to both bruising and thumbnail damage. Adrian Cunnington, head of Sutton Bridge Experimental Unit, has been to the store to see it in action.

Handling potatoes straight from cold storage heightens the risk of bruising and splitting, so most packers have systems in place to enable rapid warming to take place. This is usually done with the aim of raising the tuber temperature to around 8°C, but logistical constraints often mean this needs to be done in a matter of hours rather than days.

But if more heat is added, using aggressive gas or kerosene-fuelled heaters for example, warming the air to in excess of 30°C, this can dry out the skins of the potatoes making them taut.  If they are then given insufficient time to recover, they will readily split on handling leaving the characteristic ‘thumbnail’ marks on the tuber skin (see picture).

What is actually needed when warming a crop up is better airflow and, if this is available, the crop can be warmed with air at a very similar temperature to that required.

This is the approach Manor Fresh, Lincolnshire-based suppliers of high quality fresh potatoes, has taken in tackling the problem in a radical new way.

Shayne Tyler, head of operations at Manor Fresh, has been working with Ray Andrews of Crop Systems, who has fitted out the refurbished warming store with a series of independently ventilated bays, each with its own inverter-driven fan.

The fan is controlled on the basis of the crop temperature loaded into the bay, determined by a single probe put into the crop by the forklift driver when the crop first comes into the warming store.

Depending on the temperature of the crop coming in, the fan speed is adjusted to suck a variable amount of air through the boxes from the store, which is maintained at a fixed 10.5°C using recovered heat from the adjoining cold store equipment. Continual ventilation keeps gradients down to a claimed maximum of 1°C, minimising the risk of condensation.

“It has been revolutionary” says Mr Tyler. “Warming of most crops is achieved within 2 to 4 days at a fraction of the energy incurred previously for the job — and the computer-control system provides paperless records to give us full traceability of crop temperature”.

The new system has been dubbed WarmStor® by Crop Systems and has been submitted for an innovation award at the forthcoming Potato Europe 2009 exhibition at Emmeloord, the Netherlands in September.

It has helped Manor Fresh reduce its energy use for warming, an important aspect given Marks and Spencer’s widely-publicised ‘Plan A’ objectives for combating climate change. This was a fact not lost on M&S chairman Sir Stuart Rose when he visited the site near Holbeach this summer.

It is indeed a major step forward. Efficient warming is a boon to any packer, but the real gain with this system is the consistent quality that appears to have come with it.

Manor Fresh believes that thumbnailing has been virtually removed and bruising is effectively controlled using the warming system. This offers the potential to make a step-change in the reduction of damage and wastage incurred in the packing sector.

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