Box Design

Large 1 tonne storage boxes for potatoes are the main commercial method of European storage. During the early 1960s there was a move from more casual storage of potatoes in large piles in growers’ sheds to neat vertical stacking of potatoes in large pallet based boxes up to 6 or 7-high in purpose-built stores. These boxes at the time typically varied from half to one tonne (1000 kg) capacity and the buyer usually dictated the exact plan size and height of the boxes, often to match that customers existing box stock.

3.1_400
1000 kg potato boxes

Now almost the entire British potato crop is stored in these boxes in purpose-built stores, whether for seed or for ware (consumption). They are block-stacked loaded up to 8 boxes high if tested to the BS Class 8, usually several boxes deep (front to back) either side of a central aisle in a large storage building. Most boxes are made from one of the European pines or UK spruce, since these species seem to suit the English crop and are able to take the large loads in the stores. The loads have to be withstood without respite for several months of indoor storage and experience has shown this intensity can only be economically met by sawn timber. Other materials such as recycled thermoplastic have not been successful due to innadequate strength under long term load.

Safety and design. During the period of change from loose-piled storage to large boxes, from the 1960s to 1992 there was no British Standard to guide potato box construction, nor any commercial guide such as a Potato Marketing Board design guide. The HSE became concerned over what they considered unsafe height stacks (at the time they felt 4-high was a safe limit) and this was causing wasted storage space and higher costs in stores originally built for 7 or 8 high. The Potato Marketing Board (later the Potato Council) supported the technical development work proposed and PalletLink successfully bid for a UK Government contract to produce the technical content for BS 7511. The aim of the BS was greater stack height with appropriate safety which would result in lower cost and safety. The Potato Marketing Board chaired the technical committee (its members including box manufacturers and timber suppliers) which guided PalletLink work throughout the 2 year project.

In 1992 after a substantial amount of testing and development BS 7611: Potato storage boxes for mechanical handling was published, it reflected industry needs and listed several plan sizes each of 1000 kg capacity. These, in the strongest well braced constructions permitted stacks up to 8-high maximum. The BS 7611 is now considered a benchmark for box construction by box manufacturers, potato growers and supermarket processors. 

Zero chemical treatment. Under cover with ventilation wood boxes are long lasting. however wood can decay with inapropriate storage (debris such as old tubers remaining in boxes left outside) and a past remedy by some growers, was to obtain timber boxes treated with chemical preservative. However, this is now strictly not permissible as there are as yet no preservative treatments permitted by the UK or EU for use with timber in contact with foodstuffs. Note that boxes used for seed potatoes are indistinguishable from preservative-free boxes produced for human consumption and 1 tonne seed boxes are the same size and design as boxes used for potatoes for human consumption and may easily end up in the food-chain.

There is an EN standard (also a UK standard) aimed at food processors and supermarkets requiring packaging users to audit any chemicals in packaging, this is EN 15593: Management of hygiene in the production of packaging for foodstuffs - Requirements. There have been several claims for damages and loss of business where traces of wood preservatives have been found in foodstuffs. The marking of all seed boxes at manufacture if preservatives have been used (as SEED ONLY) would be beneficial and likely to be in any revision of th BS 7611.

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PDF31a Agricultural Produce Storage Box Terminology. (PDF 56kb)
PDF31d BS 7611 testing requirements on bulk 1 tonne potato boxes. (PDF 125kb)
PDF31g Avoiding wood decay in potato storage boxes. (PDF 30kb)
PDF52j International strength levels for pallet & box nails. (PDF 72kb)
PDF78b Natural Durability of Timber used in pallets and packaging. (PDF 26kb)
PDF79b Bending strength properties of softwoods. (PDF 32kb)
PDF81h The causes of bluestain in packaging timber. (PDF 83kb)
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