Long-term storage of sugar beet in North-West Europe
In the countries of Western Europe, sugar factory operations have been extended to mid-January and therefore sugar beet have to be stored for about two months. This report presents a review of current knowledge and research into methods to lower sugar losses and optimise the conditions for long-term storage.
Sugar losses during storage can be quantified as respiration losses in air-tight vessels, under controlled conditions or in field clamps. For quality assessment, the standard analyses (sugar, potassium, sodium and amino nitrogen) should be extended to include at least analysis of invert sugars (glucose + fructose). Additional information can be obtained from visual assessment of beet injuries (especially root tip losses) before storage, and of sprouts, frozen parts, moulds and rot after storage.
During storage, sugar is degraded by enzymes. In the first days after harvest, sugar losses occur due to wound healing and thereafter respiration declines. Further sugar losses mainly depend on the storage temperature. Storage at 2 to 8 °C is regarded as optimal. In addition to the sugar losses, strong accumulation of invert sugar occurs, which severely affects processing. Sugar losses are markedly enhanced when sprouting, rotting and infection by bacteria and fungi occur. Rotten and, in particular, frost-damaged beet cannot be stored further and have to be processed immediately. Mould formation and the subsequent rotting and reduction in quality drastically increase above an accumulated thermal time of 270 degree days (base temperature 0 °C).
Sugar beet varieties differ in storability, possibly due to their susceptibility to damage and/or infection by moulds and rot. Storage losses are also strongly dependent on the beet growing conditions (location/soil, stress during the season, harvesting conditions). Root injuries during harvesting and clamping should be minimised, as they markedly increase rotting and thereby sugar losses. Complete removal of leaves, possibly in combination with slight topping, gives the lowest sugar losses during long-term storage, as over-topped beet are avoided. Treatment with lime during clamping can reduce pathogen infections.
Recommendations for optimal harvest and clamp management include protecting clamped beet from precipitation. Clean, dry beet allow gas exchange, which prevents heat accumulation and lowers the infection potential of moulds and rots. Frost damage should be avoided by harvesting the beet in time and covering the clamp with e.g. plastic sheeting, fleece, straw or canvas, which can provide some protection against frost.