There are two methods for extracting fruit juice: pressing and leaching. For most fruits and vegetables with rich juice content, pressing is the main method, the method of extracting juice varies with the type of raw materials and the scale of production; For fruits and vegetables with low fruit juice content, the method of adding hot water for leaching after crushing the raw materials is adopted, the amount of water added, leaching time and leaching temperature depend on the type of fruit and vegetable.
Juice Pressing Method
The juice pressing method is using external mechanical pressure, squeezing fruit and vegetable juice from fresh fruit and vegetable or fruit and vegetable mash. The two processes of pressing and filtration are usually combined, so the juice pressing method is also called the squeezing filtration method.
The pressing effect depends on the fibrous structure, the variety of the fruit and vegetable, the maturity, freshness and the squeezing conditions of the press, including pressure, filtration pore size, etc. Since juicing and coarse filtration are carried out simultaneously, the penetration amount of the squeezed fruit and vegetable pulp residue and the amount of juice penetration through the capillary pores are very important to form a fast juice flow. The juicing process is different according to different fruit and vegetable raw materials. Some fruit and vegetable juices have artesian juice, and the juice begins to be produced before pressing.
During the pressing process, the pressure acting on the fruit and vegetable pulp varies, since the solid particles of fruits and vegetables are full of voids, the pressing pressure increases slowly at the beginning of the squeezing, as the pressing progresses, the air and juice in the voids of the fruits and vegetables are continuously squeezed out and separated from the formed flow channels, and the pressing volume is reduced, the remaining fruit and vegetable pulp residues are compressed and the extrusion force increases rapidly.
The squeezed fresh juice contains suspended solids and coarse particles, which require coarse filtration or sieving. The squeezed juicer is generally equipped with a filter screen, and the filter screen aperture can be customized between 0.3-2mm, so as to adapt to different fruit and vegetable solids separating.
Juice yield rate is the most important economic and technical index for extracting fruit and vegetable juice. In the juice pressing method, in addition to the texture, variety, maturity, freshness, and juicing method of the fruit and vegetable, the squeezing force and the squeezing speed of the juice press machine, the fruit and vegetable crushing degree, the paving thickness are also the main factors affecting the juice yield.
Juice Leaching Method
Extraction/Leaching is also the most common method for extracting juice from raw materials of fruits and vegetables. For fruit and vegetable juices with low water content, such as hawthorn, dates, ebony, tea leaves, and herbs, which are difficult to extract juice by pressing method, are mainly use the leaching method to extract the juice.
The leaching method is to immerse the broken fruit and vegetable raw materials in water. Due to the concentration difference between the soluble solids content in the fruit and vegetable raw materials and the dipping juice, according to the diffusion principle, the soluble solids in the fruit and vegetable cells are immersed into the juice through the cells.
The main factors affecting the extraction effect are the amount of water added, the extraction temperature, the extraction time, and the degree of fruit crushing. Taking the date palm as an example, the fruit and water ratio during extraction is 1:2, the extraction temperature is 60-80 °C, the extraction time is 1.5-2 hours for one time, and the total time for multiple extractions is 6-8 hours. The leaching process is carried out in a leaching tank, after the fruit mash is mixed with hot water, then start stirring to let the soluble sugar flow out. After the fruit is crushed, the chance of fruit pulp contact with water increases, which is beneficial to the extraction of soluble solids. Therefore, it is necessary to use a crusher to properly crush the fruit before the leaching.
