Preserving potato skin finish during storage

The term ‘skin finish’ relates to the visual appearance of the potato tuber. More specifically, a good visual appearance is attributed to an intact tuber skin without physiological or pathological blemishes. Factors that are normally considered when evaluating skin finish include: blemish diseases, shine (or bloom), netting, and appearance of lenticels. This literature review, published in 2006, covers:

• implications of periderm development and structure;
• methods of assessing skin finish;
• bloom;
• netting and russeting;
• appearance of lenticels;
• effects of blemish diseases;
• effects of crop husbandry on skin finish at store intake;
• changes in skin finish during storage;
• considerations at store unloading.

Blemish diseases such as black dot (Colletotrichum coccodes), silver scurf (Helminthosporium solani) and skin spot (Polyscytalum pustulans) increase during storage. However, it is important to minimise the development of these diseases in the field in order to obtain the best skin finish out of store. This is best achieved by minimising the growing period of the crop. Blemish disease control is also possible during the early storage phase. This is done by either rapidly cooling the crop (i.e. black dot and silver scurf) or adequately curing the crop (i.e. skin spot) soon after loading into store. Deciding which strategy is best will depend on whether factors such as variety, seed health, and previous cropping history indicate a risk of skin spot.

Factors, other than diseases, that affect skin shininess, netting/russetting and enlarged lenticels include: variety, soil texture, planting depth, nutrition, soil temperature, water stress, water logging, length of growing season, and curing regime after store loading.  The most important of these factors are variety, soil type and water stress (irrigation scheduling and water logging). For example, water stress should be minimised, especially fluctuations in water stress, and water logging should be avoided by good soil management. Soil types that produce tubers with good skin finish are those that have a high water holding capacity and a low sand content (low abrasiveness).  However, there is currently no good, objective information on suitability of soils for best skin finish.

Rapid cooling during early storage has been shown to delay the loss in skin shine. Maintaining a high humidity during storage did not produce any consistent effects on skin appearance. However, storage at 98% RH reduced crop weight loss compared with storage at 90% RH. 

The review refers to pesticides that may no longer be used in GB. Please refer to the Health and Safety Executive, Chemicals Regulation Division (CRD) website for up-to-date information on the plant protection products authorised for use in GB.