How to make fried dried vegetables?
Technical Principle
Low-temperature vacuum frying combines the vacuum and deep-frying processes. Under vacuum, the air pressure drops, significantly lowering the boiling point of water. Water boils at 100°C at normal pressure, but under a vacuum of 0.09 MPa, it drops to around 40°C. In this environment, moisture from the vegetables evaporates rapidly at low temperatures, achieving rapid dehydration. Simultaneously, cooking oil acts as a heat transfer medium, ensuring even heating of the vegetables. During this process, moisture rapidly escapes from the vegetables, creating a porous structure that gives them a unique crisp texture. For example, when vacuum-frying carrot slices, moisture rapidly converts to steam under the low-temperature vacuum and escapes, leaving behind countless tiny pores that create a crisp texture.
Production Process
Raw Material Selection
Select fresh, appropriately mature vegetables that are free of pests, diseases, and mechanical damage. For example, when making okra slices, choose fresh, tender, medium-length, and spotless okra. When making sweet potato slices, choose sweet potatoes with smooth skin, no sprouts, and no rot. The optimal ripeness of different vegetables depends on their characteristics and product positioning. For example, bananas for deep-frying should be ripened within 7-8 minutes to achieve peak sweetness and flavor.
Washing and Cutting
Rinse vegetables under running water to remove any dirt, impurities, and pesticide residue. Cut precisely according to product specifications to ensure uniform shape and size. For example, carrots are typically cut into 3-5 mm thick slices, and green beans into 5-6 cm long strips. This ensures even heating during deep-frying and consistent product quality.
Enzyme Inactivation Pretreatment
To prevent browning and preserve color and quality, enzymes are typically inactivated by blanching, steaming, or soaking in chemical solutions. Blanching temperatures are generally 95-100°C, and the blanching time varies depending on the type of vegetable and the size of the cut pieces. For example, spinach requires 30-60 seconds, while potato cubes require 2-3 minutes. Some vegetables can be quickly frozen to inhibit enzyme activity, for example, by quickly freezing the cut vegetables in a freezer below -18°C.
Vacuum Frying
Pre-processed vegetables are placed in a vacuum fryer, sealed, and the vacuum pump is activated to generate a vacuum pressure of 0.08-0.095 MPa. Simultaneously, the heating system raises the oil temperature to 80-110°C. The frying time varies depending on the type of vegetable, thickness, and moisture content. For example, pumpkin slices require 8-12 minutes, while purple potato slices require 10-15 minutes. During the frying process, the moisture in the vegetables is rapidly evaporated, resulting in a porous, crispy texture.
Vacuum De-oiling
After frying, the vegetables are rapidly de-oiled using a vacuum centrifugal de-oiler. High-speed rotation generates centrifugal force, separating the oil adhering to the surface of the vegetables and reducing the oil content. The de-oiling process typically takes 5-10 minutes, with the speed controlled between 1000-2000 rpm to ensure effective de-oiling without damaging the vegetable structure.
Cooling and Seasoning
After de-oiling, the vegetables are air-cooled or allowed to cool naturally to room temperature. Seasonings such as salt, sugar, pepper, and tomato powder are added as needed based on market demand and consumer taste. Stir thoroughly to coat the vegetables with the seasoning, enhancing the flavor.
Packaging and Storage
Use vacuum or nitrogen-filled packaging to isolate the vegetables from air, moisture, and microorganisms. Use a composite material with good barrier properties, such as aluminum foil. After packaging, store the product in a cool, dry, and dark place to prevent oil oxidation and moisture deterioration, ensuring stable product quality throughout its shelf life.
