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Improvements relating to packaging of potatoes

Potatoes are often sold in sealed packs formed from a transparent plastics material which is liberally punctured with relatively large holes to allow the pack to "breathe", which is believed to be necessary in order to minimise deterioration of the product. However, packaging in a transparent bag provided with air holes tends to encourage greening and sprouting of the potatoes due to the exposure to light under normal atmospheric conditions. If potatoes are packed in a totally sealed and close fitting bag, then the potatoes will deteriorate rapidly due to anaerobic bacterial action.
It is an object of this invention to provide a means of packaging potatoes which enables them to be maintained for useful periods of time without significant deterioration.
According to the present invention there is provided a method of packaging potatoes, wherein the potato and atmospheric air, or a comparable oxygen containing gas, are sealed in a pack formed from sheet material which is impermeable to the gas, or semi-permeable to oxygen, such that a predetermined controlled environment is established, with the oxygen volume, at the packing stage, being between about 4 to 15% of the potato volume.
The invention further extends to a pack incorporating potatoes, as created by the packaging method as hereinbefore defined. Such a pack comprises one or more potatoes and atmospheric air, or a comparable oxygen containing gas, sealed in a pack formed from sheet material which is impermeable to the gas, or semi-permeable to oxygen, and containing a predetermined controlled gas environment with an initial oxygen volume between about 4 to 15% of the potato volume.
The quantity of oxygen provided within the pack allows the potato (which is a living organism) to develop slowly and also avoids creation of conditions which lead to rapid decay. Furthermore, the control of the atmosphere within the pack substantially reduces the rate at which greening or sprouting may occur. This is essentially because the carbon dioxide level increases slowly over a period of time and this retards the greening process. For one type of preferred product, the sheet material will be impermeable to the gas since this provides an added advantage that the pack can be retained as an enclosure for potatoes during the cooking process (such as boiling or baking) . The flavour and goodness of the potato is then retained, rather than being lost to some extent during the cooking process. If the sheet material is of a semi-permeable nature, then normally the pack will only be suited for retaining the potatoes during cooking achieved by the microwave process. The level of oxygen within the gas is of significant importance in achieving a balance between creating the conditions where decay is likely and conditions where undue activity of the potato is experienced. A more preferred limited range for the oxygen volume (compared to the volume of potato) is 4 to 12% with the optimum being near 9%. It is also desirable that the initial carbon dioxide level should be less than 5%. In atmospheric air the remainder of the gas is largely of an inert nature but, if a particular non-ambient gas atmosphere is created, desirably this will incorporate an inert buffer gas having a volume at least three times that of the level of oxygen. For example, the inert gas may essentially be nitrogen at a level of 70 to 75% of the total gas volume. By packing the potatoes in the manner indicated above, it is envisaged that the potatoes can be stored without change to an unacceptable condition for well over ten days on the sales shelf.
The sheet material will ideally be formed into a sleeve which is sealed at both ends to enclose the potatoes and the gas atmosphere. This enables packaging to be carried out by a flow wrapping technique. The bag will normally have to be fairly robust and so the sheet material is ideally of a high tensile strength. If it is envisaged that the potatoes are to be cooked within the bag, then the sheet material will ideally be heat resistant to break-down up to 200°C, whilst allowing for heat sealing at a temperature of perhaps 110 to 150°C. A preferred type of sheet material for the bag is a polyester film sold by ICI under the Trade Mark MELINEX 850. In the packaging process the potatoes will need to be thoroughly washed (probably by a double washing technique) if it is intended that the potatoes should be cooked without further preparation. The strict hygiene requirements of very clean operating conditions in a closed environment at the packing station can result in significant usage by the operators of the normal atmospheric oxygen. In such circumstances, is is planned that the oxygen level within the packing station should be sampled at regular intervals so that the oxygen level at the point of packing within the sheet material can be augmented by injection of the required quantity of oxygen.
Whilst the invention may be performed in various ways a preferred embodiment thereof will now be described with reference to the accompanying drawings in which:- Figure 1 is a plan view of a potato packaging plant embodying this invention;
Figure 2 is a side view of a wrapping section of the packaging plant of Figure 1; and
Figure 3 is an illustrative view of a packaged potato in accordance with the invention.
For the process of packaging potatoes the potato is first fed by a conveyor 1 (Figure 1) to an initial washing station 2 embodying a rotatable drum 3 incorporating water to wash the potatoes as they tumble around in the drum 3. The potatoes then pass by a conveyor 4 to a secondary washing station 5 incorporating another rotating drum 6 which contains chlorinated water (or other suitable bactericide in water) which will reduce the bacterial and fungal growth on the potato to an acceptable level. As the potatoes pass out from the washing station 5 on a conveyor 7 they ar~ subjected to a drying process, by means of an air "knife" 8 which blasts off liquid on the surface of the potatoes.
The conveyor 7 leads to a grading station 9 where the potatoes are graded for size and pass to respective output conveyors 10. This grading can be automatic by means of size or weight or can be achieved by eye. Each conveyor 10 leads to a wrapping station 11 where a sheet of plastics material 12 (Figure 2) is flow-wrapped around the potatoes carried along a travelling platform or roller bed or conveyor 13. The sheet 12 is passed up through a slot 13A in the conveyor 13 and a sealing unit 14 heat seals the edges of the sheet 12 together below the conveyor 13 to form an edge portion 15. The leading edge of the sleeve formed from the sheet 12 is heat sealed by a further unit 16 and, after a potato has passed the unit 16, the trailing edge is also heat sealed to form an enclosed bag which is cut off from the rest of the sheet following behind. An air probe 17 ensures that the required volume of the gas to provide a predetermined preferred level of 9% of oxygen in the sealed bag is achieved immediately before sealing.
The form of the bag 18 enclosing a potato 19 is illustrated in Figure 3. Whilst the sheet material used to form the bag 18 will, for most purposes to be a transparent material, aluminium foil, for example, could be used as an alternative, if desired. Another possibility is to incorporate into the plastics sheet a "window" of a se i-per eable nature with minute holes which will just allow a certain amount of oxygen to enter the bag as the oxygen is used up over a period of time.
Whilst the invention has been illustrated in the drawings in relation to the packaging of single potatoes into a bag it will be appreciated that the equipment could be modified to achieve sealing into a bag of a number of

(smaller) potatoes, probably by a form filling technique rather than by flow-wrapping.