Where there is only one growing season per year such as in temperate climates, the seed potato crop with an about four-month growing season is stored for eight months. This happens in the North of America, Europe and Asia and in the South of Africa, South America, Tasmania and New Zealand. In the subtropics with a winter crop, the seed is also stored, almost for 9 months such as in West Bengal.
Upon store loading after harvest, the tubers are not immediately cooled down, but first are kept at about 18 °C to allow the skin to cure. The storage temperature of seed potatoes is as low as 2 °C but some varieties produce internal sprouts at such a low temperature and need to be stored at higher temperatures. A few weeks before planting the crop is warmed for sprouting (chitting). Table potatoes, when only stored for a few months before they start sprouting, are kept at 8-10 °C. For the longterm, the temperature is 4 °C. Often after some eight months of storage, the quality of the skin and flesh is such that consumers look for fresh potatoes from California for Canada and from Israel for the UK.
Storing in boxes
Tubers destined for frying in the processing industry are stored at 6–7 °C (chipping potatoes) and 8–10 °C (crisping potatoes). Seed potatoes are not stored in bulk higher than 3 m to avoid blemishes. For this reason, seed growers tend to store their product in boxes. In boxes seed potatoes dry better and more easily and often they occupy less volume. Moreover the product has a higher value per kilogram which incites growers to spend money on a more expensive storage system. Boxes also facilitate storing different seed lots of different varieties, sizes and health classes. Ware potatoes for processing go up in bulk to 5 m in height where storage conditions, variety and processing quality permit and depending on region and variety. In general, storing in 1–2-ton capacity wooden boxes gives the store keeper the best opportunity to maintain optimal conditions for all types of potato.
Seed tubers for long-term storage are kept at 2 °C for about eight months, table potatoes at 4 °C for a similar period, after which consumers will look for fresh tubers. Processing potatoes are kept up to 10 months to be able to supply the factories throughout the year. They are stored at higher temperatures than table potatoes to avoid the accumulation of reducing sugars responsible for the brown color of fried products. Potatoes for starch factories that often run for a limited number of months after harvest are stored outside, heaped in clamps and when stored in buildings with outside air only at temperatures comparable to other processing potatoes. Sugar formation hardly changes the specific gravity upon which payments of starch potato is based, but negatively influences the starch concentration.
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