Fruits and vegetables freeze-drying process and the lyophilizer food production process: raw material selection & rarr;
Organize & rarr;
Pre freezing & rarr;
Sublimation drying & rarr;
Post-processing & rarr;
Packaging and storage.
operation point
1) pretreatment
general pretreatment refers to all treatment before the sublimation drying, freeze also belong to pretreatment before drying.
Pretreating and conventional dry fruits and vegetables and fruits and vegetables frozen products are the same, if you need to choose, washing, peeling, segmentation, blanching, cooling, such as processing, specific operation related content, see the book in this not elaborate.
In the fruit or vegetable juice freeze-dried, with relatively low concentration, processing methods in advance will be in advance after frozen products into granular.
pre freezing is frozen processing after pretreatment of the raw material (
On freezing process and equipment see book & quot;
9.
Fruits and vegetables frozen & quot;
）
It is an important process freeze-dried.
Due to the fruits and vegetables in the freezing process will occur a series of complicated biochemical and physical and chemical changes, so the precool of good or bad will directly affect the quality of freeze-dried fruits and vegetables.
Key consideration in the process of freezing is the freezing rate of frozen materials for their quality and the influence of the drying time.
And slow frozen has the following differences: quick-frozen produce small ice crystals, slow frozen produce larger ice crystals;
Large ice crystals to sublimation, small ice crystals for sublimation;
Small ice crystals have less effect on the cell, the smaller the ice crystals, after drying can reflect the original organizational structure and performance.
But the freezing rate high, the energy consumption is high.
Should be comprehensive consideration, choose a * * * * * * of the freezing rate, to guarantee the quality of the freeze-dried food at the same time, make the required refrigeration energy consumption minimum.
2 sublimation drying is the core technology of freeze-dried food production process.
To control the process conditions:
(1) when the load is dry, the lyophilizer wet heavy loads per unit area of drying plate on the drying quality, is an important factor to determine the drying time.
The thickness of the dry food are also factors that affect the drying time.
freeze drying, the drying material is from outer to inner, therefore, be dry material thicker, need a longer drying time.
In actual dry, dry material have been cut into 15 ~ 30 mm of uniform thickness.
Dry plate should be loaded by the material quantity per unit area, should according to the heating mode and dry all kinds of food.
In industrialized large-scale device is adopted to dry, if for 6 ~ 8 h dry cycle, the dry plate material loading capacity is 5 ~ 15 kg/m2.
(2) the drying temperature
freeze drying, in order to shorten the drying time, must be needed to supply sublimation heat effectively, thus designed a variety of practical ways of heating.
Drying temperature must be controlled in order to not cause dry ice crystal melting in dry material, has been part of thermal denaturation caused by overheating.
Therefore, in a single heating mode, the temperature of the drying plate at the beginning of the sublimation of drying should be controlled in 70 ~ 80 ℃, drying medium at 60 ℃, dry late in 40 ~ 50 ℃.
3. Dry the judgment at the end of the
dry finish the following indications to determine available: basic material temperature and the heating plate temperature uniformity and maintain for a period of time;
Pump group (
Or cold trap)
Vacuum gauge and drying chamber vacuum gauge, and maintain a period of time;
Drying chamber vacuum gauge cold trap at basically reply to the device no-load temperature index and maintain for a period of time;
For the lyophilizer, with big butterfly valve can be closed big butterfly valve, vacuum machine, basic no descent or rarely.
The above four decision basis, can be used alone, can also be combined or used in combination.
(3) post-processing post-processing including discharge, semi-finished products to choose, packaging and other processes.
speed after lyophilization, the pour dry nitrogen or air break vacuum drying chamber, then immediately remove the material at a relative humidity below 50%, the temperature of 22 ~ 25 ℃, less dust discharge airtight environment, and semi-finished products in the same environment of sorting and packing.
Because after freeze-dried material with large surface area, moisture absorption is very strong, so you need to in a relatively dry environment, to complete the operation of these processes.
Packaging and storage of
(4)
freeze-dried food packing;
big food freezing dryer, freeze-drying production line equipment
the article original, reproduced please indicate the source: industrial instruments, WWW.
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