Detailed Explanation of the Key Processing Techniques for Clarified Pear Juice

(1) Process flow

Substandard fresh fruit → wash and drain → sort and trim → crush → color protection → press → coarse filtration → clarification → fine filtration of clear juice → ingredient adjustment → bottling → exhaust → seal → sterilize → cool → finished product

(2) Explanation of operating points

(1) Washing and sorting of pears: Washing removes the soil and pesticide residues carried on the peel, reducing the microbial count to 2.5%-5.0% of the original. Washing methods include flume rinsing, brushing, and spray washing, and several methods are often used in combination. The main purpose of sorting is to remove rotten and mechanically damaged fruit and eliminate impurities. Manual selection is mostly used.

(2) Crushing and color protection: Because pear peel is relatively thick, the flesh is firm, and the stone cell content is high, the crushing step is an important step for increasing juice yield. The size of the crushed fruit pieces must be suitable, generally 3-4 mm. To prevent oxidative browning from contact between the fruit and air, color protection measures must be taken during the crushing step; generally 0.8% citric acid or 0.08% vitamin C is added, or potassium metabisulfite (added at 100 mg/kg) may also be used for color protection. Crushing equipment includes hammer crushers, toothed plate crushers, and centrifugal crushers.

(3) Juicing: Juicing is an important part of the juice-making process, generally requiring high juice yield, good juice color, and minimal nutrient loss. Because the fruit has a relatively high pectin content, pressing directly for juice after crushing gives a low juice yield and cloudy juice, so 0.2% pectinase may be added to break down the pectin, with enzymatic hydrolysis at 35-45°C for 2 hours. Commonly used juicers at present include wrapped presses, horizontal cylindrical presses, screw presses, and belt presses.

(4) Clarification: Clarification is the most critical step in the juice-making process. After coarse filtration, the juice often contains some suspended matter and colloidal particles, whose main components are cellulose, protein, enzymes, sugars, pectin, and other substances; their presence seriously affects the transparency and stability of the juice. Methods used include: 1) diatomaceous earth clarification: dosage not exceeding 420 g/1000 L; 2) gelatin-tannin method: the optimal amounts of 0.5% gelatin solution and 1% tannin solution are 7.5% and 7%, respectively.

(5) Filtration: After clarification, the pear juice still needs the precipitate and unstable suspended particles removed. A diatomaceous earth filter gives the best filtration effect, with a diatomaceous earth dosage of about 0.01% and a filtration pressure of 0.3-0.35 MPa. A plate-and-frame filter is also one of the commonly used devices, and ultrafiltration equipment may also be used.

(6) Sterilization: Pasteurization and high-temperature short-time sterilization may be used. Short-time sterilization: about 93°C, 15-30 seconds; commonly used equipment includes tubular heat exchangers and plate heat exchangers. Filtration has the effect of cold sterilization.

(7) Filling: Three forms may be used: hot filling, cold filling, and aseptic filling.