ITDG 
Interdev Agroalimentaire  

Production of fruit leathers

	Type de fiche	Techniques/Technologies
	Mise en œuvre	ITDG(Royaume Uni)
	
	Zone géographique	Global; 
	Mots clés	FRUIT; FRUIT SECHE; CUIR

	Echelle d’action	Global
	Public(s) cible(s)	Small- and medium-scale food processors

Contexte
Fruit Leathers are made by drying a very thin layer of fruit puree to produce a product with a texture similar to soft leather. Fruit leathers are eaten as a snack and are often targeted at health food markets, using marketing images such as "pure", "sun dried" and "rich in vitamins".  Such claims are not unreasonable given that low temperature drying is a gentle process that results in less loss of nutrients than, for example, canning in which up to 65% of minor nutrients can be destroyed. Losses of vitamin A and C are, however high, if the fruit is dried in direct sunlight.  Fruit leathers can be made from one type of fruit or blends of different fruits. They have a soft rubbery texture and a sweet taste, with the distinctive flavour and colour of the raw material.  Most fruits can be used for the production of leathers, including banana, mango, apricot, guava, pineapple and papaya.  They may be sweetened, by adding sugar or flavoured with chopped nuts, coconut or spices.

The preservation of fruit leathers depends on their low moisture content, typically 15 to 25%,  the natural acidity of the fruit used and high sugar contents. The products have a shelf life of up to 9 months provided they have been sufficiently dried and properly packaged.

The preservation process is very simple and basically involves the production of a sugar rich fruit puree, which is subsequently dried.  Both the addition of sugar and drying decrease the amount of free water available and therefore prevent the growth of spoilage organisms.

Problématique / Objectifs
It is important to select ripe fruits.  Overripe ones can easily become damaged and bruised.  Under-ripe fruits will not have the full flavour and the colour may be poor.  If bananas are used, they should be harvested before they are fully ripe, with the skin a little green. 

A high quality product can only be made from good quality raw materials and production should not, as too often happens, be based on second grade fruit that is not suitable for the fresh market. Fruit that has been rejected for being too large, too small or because of surface blemishes is, however, usually acceptable.

Fully ripe soft fruits are very susceptible to bruising when handled and bruised areas will quickly begin to rot. It is thus better to purchase semi-ripe fruit (which is usually cheaper) and allow it to fully ripen in the processing area. This also has the advantage of allowing the daily selection of fruits of equal ripeness.

Description/Mise en oeuvre
1. Selection, preparation and intermediate storage
Incoming fruit should be selected and any unsuitable material removed from the processing area and properly disposed of; not simply put in an open bin outside. Selected fruits are then washed in chlorinated water (one teaspoon of bleach per gallon of water) and then peeled, de-stoned etc, depending on the type being used. Only stainless steel knives should be used as mild steel will corrode and stain the flesh.  Some fruits require special attention. Banana has a very low level of acidity and is also subject to what is known as enzymatic browning which results in rapid discoloration after peeling and cutting.  After peeling, bananas should be quickly immersed in water containing a small quantity of a chemical, sodium metabisulphite, which controls such browning. The solution should have a concentration of 400 parts per million of sulphur dioxide.

Use of Sulphur dioxide (SO2)

SO2 has been widely used in fruit and vegetable products to control enzymatic colour changes such as the darkening of a freshly cut apple or potato. It also acts as a preservative, controlling the growth of moulds and yeasts. SO2 is produced by either burning a small piece of sulphur or by dissolving sodium metabisulphite in water.  The second method is more controllable.

The levels of SO2 used are measured in parts per million or ppm. Concentrations of 400-1000ppm are used for dips to control colour changes and retard the growth of moulds and yeasts.  A 400ppm bath is made by dissolving 6g of sodium metabisulphite in 10 litres of water.

NB. SO2 gas is harmful if breathed in, it should only be used in a well ventilated room

In recent years the use of SO2 has been increasingly controlled and it has been banned in many foods in the USA. Similar changes to food laws are is likely in Europe.  In such situations browning can be controlled by the addition of citric acid but this is far less efficient than sulphur dioxide.

Red fruits should not be treated as both acid dipping and sulphuring bleach the red colour.

The length of time for sulphuring varies according to the size and thickness of the fruit pieces.

2. Preparation of puree
At the simplest level fruit may be pulped to a puree by hand using a food mill, or Mouli Legume mill, in which the food is pushed through a mesh by a rotating paddle. If electric power is available a food liquidiser, followed by sieving will greatly increase production outputs. At larger scale, powered high-speed blenders are recommended.

The puree should be heated to 90 0C to inactivate enzymes and reduce the level of micro-biological contamination.  The use of a double boiling pan is recommended to avoid burning that can occur if direct heating is used.

The next step is to prepare the batch. In many cases the flavour of fruit leathers is improved if the acidity is increased by adding a small amount of lemon or lime juice. Many producers mix fruit with semi-ripe banana. This reduces the cost of the product and the high solids of the banana reduces the drying time.  Other ingredients, such as sugar, spices and nuts are added.

Finally the fruit puree is poured in a thin layer, approx. 3 to 6mm thick, onto plastic trays or wooden trays lined with grease proof paper or plastic sheet. Some producers cover the whole of the tray and cut the dry product into squares. Others pour the puree in circles about 20cm in diameter and roll them when dry.

3 Drying
It is recommended that fruit leathers are not dried in direct sunlight as there will be considerable loss of colour and vitamins A and C. Several types of indirect dryer, either solar or mechanical, are available and are suitable for drying this product.  

After about a day or so in a solar dryer, or 5 hours in an artificial dryer, the leather sheet can be lifted away from the tray.  At this stage the product should be turned over and dried on the other side. Prior to packing fruit leathers are frequently lightly dusted with starch to reduce their stickiness.

4. Packaging
Fruit leather is normally sold in the form of a roll interleaved with greaseproof paper to avoid it sticking together. Strips of the required weight are laid on a piece of greaseproof paper and simply rolled with the paper. They can also be cut into small pieces and sold for use in confectionery and baked goods. Layers of fruit leather from different raw materials can be sandwiched together to form a type of confectionery product.  The final product should be packed in polythene or polypropylene heat-sealed bags.  The latter, if available, are preferred as they provide greater protection against moisture. The bags should then be placed into outer boxes to protect them from light. The product should be clearly labelled stating, as a minimum, the name of the product, net weight, ingredients list and the name and address of the manufacturer.  Where available, self-adhesive labels are recommended.

See fiche ?? for a detailed flow sheet of the production process

Résultats/Eléments chiffrés
The following pieces of equipment are required;
  Drier
  Large plastic food grade bowl for sulphur dipping
  Large stainless steel pan for boiling
  Weighing scales
  Liquidiser or pulper
  Thermometer
  Refractometer
  Food grade bins for intermediate storage of pulp

Enseignements
  Fruit leathers provide an attractive alternative option for small-scale processors of fruit.  However, as with all new products, it is essential to carry out a market survey to determine the potential demand for the product before starting production.  It is not enough to base the production on seasonal gluts of fruit. 

  The most convenient production plan for very small producers is to use fruits that are in season at any given time. This does, however, have disadvantages that include: 

  one particular flavour of fruit leather may be much more popular than others
  it will only be possible to produce small quantities of product in a short season

  It is, however, possible to produce all year by preserving prepared fruit (or fruit puree) in sealed drums with added  SO2 at a level of 600ppm. Fruit may be stored for many months in this way. Intermediate preservation also allows fruits to be purchased at the peak of the harvest when prices are at their lowest. While most of the SO2 absorbed during intermediate preservation will be lost during drying it is recommended that purees made from preserved fruits should be briefly boiled prior to drying to reduce the level of residual SO2.

Auteur : Sue Azam Ali
Saisie le : 05/12/2001
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