Effects of skin coatings on the behaviour of apples in storage. 2. Common storage investigations.

Abstract

Apples of several varieties, particularly Granny Smith, were held in common (unrefrigerated) storage after treatment with skin coatings. Under favourable conditions their storage life was increased by about 50 per cent., the greatest increase being with early varieties. Undesirable side effects are described and their relation to storage conditions discussed. The most important factors influencing the storage behaviour of coated apples were temperature and maturity. Temperatures above 70°F, even for comparatively short periods, led to fermentation and alcoholic breakdown. Fruit picked at the optimum stage for cool storage held best after coating; picked either before or after this stage, it developed disorders in storage. The best coating tested was an 8-10 per cent. alcoholic solution of 2 parts of castor oil and 1 part of wax-free shellac (C.O.S.). It was satisfactory with most varieties in cool conditions, but sometimes caused slight spotting at the lenticels. Emulsions of medicinal-grade paraffin oil, alone or mixed with castor oil, were satisfactory on most varieties (e.g. Granny Smith) which develop a copious natural waxy coating. Waxes were also applied as emulsions; the best was a mixture of 2 or 3 parts of paraffin wax with 1 part of carnauba or lac wax. Emulsion coatings were generally improved by adding 25 per cent. of wax-free shellac in 3 per cent. ammonia. C.O.S. was more effective than oil coatings and both were more effective than waxes in retarding ripening and in controlling disorders of senescence. Waxes reduced shrivelling much more than the other coatings. All coatings controlled Jonathan spot and greatly reduced bitter pit. Only the alcoholic solutions reduced mould, which was often increased by emulsions.