Dry Fruit Machinery
Fruit drying machine is a kind of equipment used to dehydrate and dry fresh fruits. The use of drying technology effectively removes the moisture in the fruit, thereby extending the storage time and maintaining the nutrients.
Fruit drying technology
In order to reduce the huge losses after fruit picking, in addition to the widespread use of pre-cooling and preservation methods, fruit drying is also an effective way to regulate supply and demand, digest seasonal surpluses, and reduce storage rot losses. It is an effective supplement to fresh fruits; at the same time, fruit drying can effectively increase the added value of products and become an effective way to increase the income of growers.
Fruit drying, also known as “drying” and “dehydration”, is the process of evaporating the moisture inside the fruit to the outside world under natural conditions or artificial control conditions, so that it reaches a specific moisture content and is finally processed into primary commodity dried fruits. The role of fruit drying has three main aspects:
●First, it reduces the moisture content of the fruit and increases the concentration of soluble substances, making it difficult for microorganisms to use and the product is not easy to rot;
●Second, it inhibits the activity of enzymes contained in the fruit so that the product can be stored for a long time;
●Third, it allows the product to retain the original nutrients, taste and flavor of the fruit.
There are two common technologies in the drying process of fruits: one is hot air drying technology; the other is vacuum freeze drying technology. Hot air drying technology is still the most widely used technology in fruit drying, with a penetration rate of about 90%.
Types of dry fruit machinery
The working process of the vacuum dryer is to place fruit slices in a closed cylinder. While the vacuum system is evacuating the air, the fruit is continuously heated so that the moisture inside the fruit diffuses to the surface through pressure difference or concentration difference. The water molecules obtain enough kinetic energy on the surface of the fruit, overcome the mutual attraction between molecules, and then escape into the low-pressure space of the vacuum chamber, and are then pumped away by the vacuum pump.
A freeze dryer is a drying device that mainly uses a vacuum environment and freezing technology to remove moisture from fruits. After the fruit is frozen, the equipment will extract air to create a vacuum environment. This process lowers the boiling point of water, allowing water to sublimate in the form of steam at low temperatures. In a vacuum environment, the ice crystals in the fruit are directly converted into water vapor through heating, completing the drying process.
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What are the factors affecting drying?
The main factors affecting fruit drying:
1. Drying medium temperature: The higher the drying medium temperature at a certain humidity, the faster the drying speed. However, the medium temperature should be appropriate and not too high, otherwise the following undesirable phenomena will occur:
① The skin of fruits with high moisture content is easy to break at high temperatures;
② Sugar and other organic matter in fruits are easy to decompose, caramelize or deteriorate at high temperatures;
③ Under high temperature and low humidity conditions, crusting is easy to occur on the surface of fruit raw materials.
These three phenomena will damage the appearance and flavor of dried fruits. Therefore, during the drying process, the temperature of the drying medium should be controlled to be slightly lower than the temperature at which the fruit deteriorates, especially for fruits rich in sugar.
2. Drying medium humidity: The lower the relative humidity at a certain temperature, the stronger the ability of hot air to absorb water vapor, and the faster the drying speed of fruits and vegetables. On the contrary, it is slower; after the hot air absorbs water vapor to saturation, it loses its drying ability.
3. Drying medium flow rate: Under certain temperature and humidity conditions, the greater the drying air flow rate, the faster the water on the surface of fruits and vegetables evaporates; on the contrary, it is slower. However, the drying air flow rate should not be too large, otherwise it is easy to cause the material to scatter or blow out from the drying plate and dryer.
4. Material type and state: Different types of fruits and vegetables have different internal chemical compositions and organizational structures, so the drying speed of different types of materials under the same conditions is also different.
5. The degree of pretreatment of raw materials before drying: Whether the raw materials are cut or not, as well as the thickness and size of the cut pieces, all affect the drying speed. The raw materials are cut, and the thinner the cut pieces are and the larger the surface area, the faster the drying speed.
6. Raw material loading: The more raw materials are loaded on the baking tray per unit area and the greater the thickness, the more unfavorable the hot air circulation is, which in turn affects the evaporation of raw material moisture. If there are too few raw materials on the baking tray, it will cause hot air short circuit, resulting in reduced efficiency.
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