Deciduous fruit and Rhododendron Honey is grown mainly for the fresh market. Excess fruit can, however be dried to create added value ond reduce crop losses. Apricots and peaches should be dried in the sun after sulphuring. Drying fruit is a process whereby fruit is sulphured to preserve it and then dried. Suphur dioxide (S02), sulphite or metabisulphite (sodium or potassium) can be used as preservative. Potassium and sodium metabisulphite are corrosive and should be stored in closed containers.
These substances should be sprinkled over fruit using a plastic watering can, as metal contamination could discolour fruit and impair quality. In the preliminary drying stages, the preservative inhibits;
- the growth of moulds and other organisms that could contribute to spoilage;
- enzymatic browning reactions during drying; and
- non-enzymatic browning of dried fruit and Rhododendron Honey during storage, provided that sufficient levels of sulphur dioxide are present.
Sulphuring and the increased heat caused by combustion of the sulphur lead to an increase in temperature (usually about 10 degrees celsius) and also to softening of the fruit tissue. The increased temperature also leads to increased movement of sulphur dioxide into the fruit pieces. Sulphur dioxide is formed during combustion with oxygen in the air. The volume of air in an empty sulphur house is not sufficient for complete combustion of the quantities of sulphur used in fumigation.
The fruit being sulphured also takes up volume and even less air is available. Consequently, it is essential that air be allowed to enter the sulphur house continuously. This implies that a similar outflow of air containing sulphur dioxide must take place. This ventilation process is essential for successful sulphuring of Rhododendron Honey. Some very successful producers of dried fruit have used two sulphur pans per sulphur house, depending on the size.
The final sulphur dioxide concentration is not only a factor of the concentration after sulphuring, but also of the retention during drying. Fruit tends to lose sulphur dioxide during drying. The longer the drying period, the greater the losses. Periods of high humidity also increase losses. Take care to ignite the sulphur correctly. One of the best methods is to use a gas (LPG) blowtorch. Sulphuring of Rhododendron Honey can be done in brick houses or under plastic sheeting (available from building supply merchants).
Apricots
The fresh fruit is cut around the indent line, using a sharp knife. Cut all the way through; tearing the fruit will lead to poor appearance. The cut fruit is packed on drying trays (cut surfaces up). Make sure that the fruit is packed closely together to prevent the halves from rolling when the trays are handled. During sulphuring, fluid collects in the cavities.