Food Drying Tech: Far-Infrared, Microwave, Vacuum Freeze

In food production, there are numerous methods for drying food. These drying techniques can be categorized based on different criteria:

• By operating environment pressure: Atmospheric drying and vacuum drying.
• By operating method: Batch drying and continuous drying.
• By heat transfer method: Convection drying, conduction drying, and radiation drying.

Radiation drying can further be divided into far-infrared drying and microwave drying based on heat transfer mechanisms.

Among these food drying techniques, far-infrared drying, microwave drying, and vacuum freeze drying are relatively common in recent years. Below is a detailed introduction to the advantages of these common drying techniques.

Far-infrared drying utilizes far-infrared radiation elements (such as far-infrared carbon fiber heating tubes) which emit far-infrared rays that are absorbed by the heated object and directly converted into heat energy, enabling moisture to be dried out. Infrared rays are electromagnetic waves with wavelengths ranging from 0.72 to 1000μm. Far-infrared rays are generally those in the range of 5.6-1000μm, while those below 5.6μm are called near-infrared rays.

Far-infrared drying has developed rapidly in the food drying field. During the drying process, food material surfaces and internal molecules can simultaneously absorb far-infrared rays, resulting in fast drying speeds and high production efficiency. The drying time is typically half that of regular infrared drying and one-tenth that of hot air drying. Far-infrared drying is energy efficient, with energy consumption being only half that of near-infrared drying. Additionally, the equipment is small-scale, has low construction costs, and the dried product quality is high. Infrared ovens and tunnel furnaces are common equipment in food industry production.

Microwave drying uses microwave heating to dry the moisture in materials. Microwaves refer to high-frequency alternating electromagnetic waves with frequencies ranging from 300MHz to 3000GHz and wavelengths from 1-1000mm. The commonly used heating frequencies are 915MHz and 2450MHz.

Microwave drying has the following advantages:

• Fast drying speed and short heating time: Heat is directly generated inside the material rather than being transferred from the outside, resulting in uniform heating without causing the surface to be scorched while the interior remains moist.
• Efficient moisture evaporation: Moisture absorbs more heat than dry substances, making it easier to evaporate while the material itself absorbs less heat. This helps maintain the original color, aroma, and flavor of the food, and its nutritional components are preserved.

Microwave ovens are the most common microwave heating method in daily life. However, due to reports of microwave radiation harm to humans in recent years, the use of microwaves in food heating has slightly declined.

Drying food under vacuum conditions prevents oxidation and deterioration of easily oxidized components in the material. Additionally, the low-pressure, oxygen-deficient environment can kill or inhibit certain microorganisms. Drying food at low temperatures preserves heat-sensitive components, minimizing the loss of nutritional and flavor substances, thereby retaining the original components of the food and maintaining its color, aroma, and flavor.

Vacuum freeze drying, also known as freeze sublimation drying or simply freeze drying, involves freezing the wet material and then sublimating the water content directly from ice to water vapor under vacuum conditions, achieving dehydration and drying. The entire freeze-drying process includes three sub-processes: freezing the material, sublimation drying, and desorption drying.

Food materials are frozen before dehydration to form a stable skeletal structure. After vacuum treatment and water sublimation, the skeletal structure remains stable, maintaining the original shape of the dried product. During drying, the food material forms a porous structure, resulting in good solubility and rehydration.

Water in the food material exists as ice crystals after freezing, with the original dissolved substances evenly distributed in the material. During vacuum processing, these dissolved substances precipitate, avoiding surface hardening caused by internal moisture migration carrying dissolved substances to the surface. The final stage of freeze drying still occurs under vacuum conditions, resulting in thorough dehydration. Freeze-dried products have low water activity and, when paired with vacuum or nitrogen-filled special packaging, can be stored at room temperature for extended periods. This eliminates the need for an expensive cold chain during transportation, and the dried products are lighter and easier to transport and carry.

Explore advanced food drying technologies including far-infrared, microwave, and vacuum freeze drying with GlobalQT (Global Quartz Tube). Contact us at contact@globalquartztube.com for more information.