1. The thickness of the liquid should be thin, and the liquid should be defoamed before entering the warehouse
Soup usually contains oil, gum, starch, or protein, and is prone to foaming and high viscosity. If the plating or bottling is too thick, the internal moisture sublimation resistance is high, which can easily lead to external dryness and internal moisture, as well as collapse.
It is recommended to control the thickness of the liquid tray between 5-10mm, and it should not exceed 15mm at most.
The liquid filling capacity shall not exceed one-third of the container volume, and space for sublimation expansion shall be reserved.
After filling or reversing, stand still and defoamer. If necessary, vacuum degassing or low-speed centrifugal defoaming should be performed to avoid foam expansion and splashing when vacuuming.
If the solid content of the soup base is too low, the skeleton will be weak after freeze-drying; Solid matter that is too high is prone to thickening and slow drying. Generally, it can be controlled at around 20% -40%, and specific adjustments should be made according to the formula.
2. Pre freezing should be thoroughly frozen, and vacuum pumping and heating should not be too intense
Soup has high water content, complex ingredients, incomplete pre freezing or rapid heating, which can easily lead to bottle spraying, collapse, and poor solubility.
The pre freezing temperature usually needs to be 5-10 ℃ lower than the eutectic point of the material. For soups, it is commonly used to be -35 ℃ to -45 ℃, and kept warm for 2-4 hours to ensure complete freezing of the center.
The temperature of the cold trap should be lowered to below -45 ℃ in advance to ensure that water vapor can be effectively captured.
Vacuum pumping should be slowly reduced in pressure, and the vacuum valve should not be fully opened at once to avoid liquid boiling and splashing.
The vacuum degree during the sublimation drying stage is usually maintained at 10-30Pa, and the shelf temperature slowly increases. The material temperature must be lower than the collapse temperature/eutectic point.
The drying stage can be gradually heated to 30-45 ℃ to further remove bound water, and the moisture content of the finished product is generally controlled below 3% -5%.
3. The discharge environment should be low humidity, the packaging should be fast, and the sealing should be strict
Freeze dried soup blocks have many pores and a large specific surface area, and absorb moisture very quickly. If exposed to humid air after discharge, it will quickly regain moisture, clump, and lose flavor.
It is best to control the relative humidity of the discharge environment below 40%.
When breaking the vacuum, slowly release the pressure with dry air or nitrogen to avoid sudden influx of humid air.
After taking out the freeze-dried soup chunks, shape, weigh, and package them as soon as possible. Priority should be given to using aluminum foil composite bags, nitrogen filling, or vacuum sealing.
Store in a cool and dry place; Soup chunks high in oil, sugar, and gum are more suitable for nitrogen sealing, and desiccants can be added if necessary.
If you are making bone soup, mushroom soup, Hot and sour soup and other high oil and high salt soups, it is recommended to make a small test verification of "concentrated solids, plate thickness, pre freezing temperature, sublimation shelf temperature, and end point moisture analysis", and then put on the mass production curve.

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