Peeling of Apple

Peeling of Apple

Peeling operation is the removal of outer layer of a fruit or vegetable. There are different methods for peeling such as;

1. Peeling by hand

2. With steam or boiling water

3. With lye or alkalies (NaOH, KOH)

4. By fry caustic peeling with infrared heat

5. By flame

6. By mechanical knife peeling

7. By freezing

8. Abrasion peeling

Choosing a peeling method for apples (and the other fruits) depend on different properties. No method is completely perfect and the amount of usable food may be the difference between profit and loss for manufacturer. There is a direct relation between peel loss of given fruit and the size of it. The small sized items, due to the surface area, may lose 4 or 5 time loss from the larger item within same category and as a second factor the shape of given item has a great importance too. For example, the roughness or contours of a given item may make it almost impossible to peel completely for many different methods. The rate of injury caused by peeling method should be taken into consideration when defining the system. As a fresh fruit, apple has a high aw and this situation causes easy injured of under layer tissues. When all of these characteristic properties are considered, the most suitable method for peeling of apple is mechanical knife peeling. In addition a different apple preparation system has been developed by FMC (1988) that automatically peels, cores and slices apples in a high-speed continuous operation.

The process of getting a peeled apple begins with harvesting. After harvesting, apples are transported to the processing plant. The second step of the process is pre-processing operations. At first apples are cleaned. After cleaning, the sorting, peeling and trimming operations are applied to apple. Sizing of the apples are very important for mechanical peeling. Generally, a screen removes apples less then 6.35 cm in diameter. In peeling and coring operations, 30-35% losses of the raw material occur.

The following operation is dipping the apples into sodium sulfite solution and slicing pieces that are 9.5-12.5 mm in thickness. To obtain dried apple rings, cored apples must be sliced at right angles to the core or cut into three, four, six or eight approximately equal units. When apples are cut into more then eight equal units, the product is referred to as sliced.

To provide dehydrated apples, the moisture of apples must be less than %3. So apples dehydrated by using of a forced-air drier such as the continuous belt dryer.

The product is then compressed and packaged. Both dried and dehydrated apple products are marketed on a large scale and their utilization particularly of low moisture products has been expanding in recent years.

Flow Diagram

Drying Process


1. Harvesting

2. Cleaning

3. Sorting-grading

Apples are either dried immediately after harvest or after being held in cold and/or controlled-atmosphere storage until a convenient processing. Only artificial driers are used by commercial apple drying plants.

Water is removed relatively easily from apples to the level usually attained in dried fruit products (%10-25 moisture).

Simple driers, such as kiln or tunnel drier are commonly used to produce dried apples. Secondary processing of the dried apples to attain products with less than %3 moisture requires the use of a forced-air drier such as the continuous belt drier.

Air-drying is sufficient for products intended for bakery utilization; if faster dehydration, greater bulk density or better texture in the dried stage is required, the use of vacuum equipment is necessary.

The processing of dried apples starts with sorting, peeling and trimming fruit. Sizing of the fruit is very important for mechanical peeling. Peeling and coring losses average 30-53 % of raw material. After peeling and trimming apples are dipped into a sodium solution and then sliced to pieces 9.5-12.5 mm in thickness. (Repeated information)

Quality Control Parameters

· Water used should be free from heavy metals and other chemical pollutants. Drinking water is suitable.

· Must not remove the underlying food.

· The container in which peeling is carried out and equipments used must be cleaned regularly.

· The peeling process must not reduce the nutritional value of apple.

· Must not cause changes in color and flavor since these two properties are the major points in evaluation of fruit products.

· Apple slices are protected from browning by immersing them in water or brine for up to 30 min at 40°C. An alternative method is to draw a vacuum. Maillard reactions are the most important quality problem in dried fruits.

Quality control measurements that are unique for dried fruit products are

1. Moisture content

2. Sulfur dioxide content

3. Screen analysis

4. Physical characteristics of dried fruit

5. Reconstitution ratio

6. Bacterial count

7. Oxygen content of gas packed products.

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