What is the freeze-drying method of food?

Freeze-drying food in particular and freeze-drying in general is the whole process of separating water or solvents from frozen foods through sublimation. In which sublimation occurs when a liquid is frozen to form a solid that converts directly to a vapor.

The intermediate state in the middle is a liquid that is ignored, so it is called the sublimation process. In contrast, the conventional drying or drying method converts water into a gaseous state to increase the shelf life of food. The direct conversion from solid to gas in freeze-drying method keeps the stability and enhances the beauty of the product.
Due to the characteristics of the operating principle, today freeze-drying is widely applied in many fields. The most popular is the food industry, the pharmaceutical sector. Food after being dried saves volume, retains flavor, aroma and nutrients almost absolutely.
Working principle of freeze-drying method
Freeze-drying food is not easy. If the correct process is not applied, the finished product will not achieve the desired shape, nutrients and taste. According to the principle, food will have to go through 3 different stages, respectively, cooling, primary drying and secondary drying.

🔰Stage 1 – Cooling
Foods must be kept at room temperature before being stored. Whereas freeze-drying devices work to convert water from a solid state to a vapor state. So food needs to be frozen first to create small ice crystals.
If you follow the correct procedure, it will take about 6-8 hours to freeze food. However, some food processing enterprises have now equipped with quick freezing lines. Freezing time will be reduced several times compared to reality but still achieve the desired effect.
The freezer dryer itself will also be equipped with a freezing unit for this first stage. In addition to cooling food, the freezer also plays a role in absorbing moisture from foods.

🔰Stage 2 – Primary drying
After freezing, the food is officially put into drying. This step requires setting up the conditions to remove water crystals from the food. Depending on the type of food, the setting time and temperature will be different. People will proceed to withdraw all the air in the drying chamber to create a vacuum environment.
At the same time, the resistor will heat to raise the temperature in the drying chamber. Ice crystals that adhere to food are quickly driven by heat and form steam. The steam after flying out of the food will be reabsorbed in another part called the water trap.
The difference of the water trap lies in the temperature. This part has a temperature about 20 degrees Celsius lower than the temperature at the drying chamber environment. As a result, the steam rises, encounters the water trap, it is quickly cooled and condenses back into ice crystals. The process continues until the steam is almost completely removed from the food.

🔰Stage 3 – Secondary Drying
After the primary drying stage, the steam in the food is almost gone. However, the inside of the deep core is definitely still slightly moist. This is when the secondary drying stage – the final stage of the freeze-drying process of food. This stage proceeds by heating to a higher level. The heat level can even reach 70 degrees Celsius. The remaining moisture in the food will be completely removed.

Advantages of freeze-drying method
The method of freeze-drying or freeze-drying brings many benefits in food processing and preservation. Especially foods that contain a lot of water such as fruits and vegetables. If drying in the traditional way, the nutrients inside and the outside of the food will be reduced to almost none.

The taste of vegetables and fruits is no longer as original as it was before, but will become supple, chewy or crunchy depending on the degree of drying. In contrast, freeze-drying food provides many benefits through:

Keep the nutritional composition including enzymes, vitamins, minerals and the same color and taste for food;

Keep the chemical and physical structure of food almost intact;

The finished product after drying has porosity, no deformation, after soaking in water, the food expands almost like the material before drying;

Food preservation time is longer than other methods.