Raw Material Requirements:
Fresh grapes are the primary raw material, combined with 20% sugar solution and 2% tartaric acid. The process is designed to maintain the natural flavor and color of the fruit while ensuring clarity and stability in the final product.
Process Flow:
The production begins with careful selection of the grapes, followed by processing, heating for color extraction, juice filtration, blending, clarification, further heating, canning, sealing, sterilization, and cooling. Each step is crucial to achieving a high-quality grape juice.
Key Process Points:
1. **Raw Material Selection**: Choose fresh, fully matured grapes that are free from rot, mold, and pests. They should have a deep color, strong aroma, and high juice content. Varieties such as red or purple grapes are preferred for their rich flavor and color.
2. **Preparation of Grapes**: After selection, the grapes are soaked in a 0.3% potassium permanganate solution for 3 minutes to disinfect them. They are then rinsed thoroughly under running water until the water runs clear. Once dried, the stems are removed, and the grapes are crushed using a crusher. It's important to avoid crushing the seeds to prevent bitterness.
3. **Heat Extraction**: The crushed grapes are placed in a container and heated to 60–70°C for 15 minutes, or to 70°C for 5 minutes to extract the pigments from the skin. This step is essential for enhancing the color of the juice. White grapes do not require this step.
4. **Juice Pressing and Filtration**: After color extraction, the juice is pressed using a mechanical press or hand press. The resulting juice is then filtered through a mesh (0.3–0.5 mm) or a velvet bag to remove any suspended solids, ensuring a smooth and clear liquid.
5. **Blending**: The sugar content of the juice is adjusted to 16% by adding a 20% sugar solution. Additionally, 2% tartaric acid is added—approximately 3.0 kg per 100 kg of juice—to prevent the formation of tartaric acid precipitates during storage.
*Preparation of 2% Metatartaric Acid Solution*: Dissolve 1.0 kg of tartaric acid in 49 kg of water, let it soak for 2 hours, then stir continuously while boiling for 5 minutes. After cooling, filter the solution through flannel and top up to 50 kg with water. Finally, cool quickly with ice water to stabilize the solution.
6. **Clarification**: The gelatin-tannin method is used for clarification. Add 4–5 grams of tannin per 100 kg of juice, wait 8 hours, then add 6–10 grams of gelatin. The temperature should be maintained between 8–12°C. Once clarified, the clear supernatant is siphoned off to remove impurities.
7. **Fine Filtration and Heating**: The clarified juice is passed through a fine filter and then heated to 80–85°C in a pan to eliminate any remaining foam and ensure a stable product.
8. **Filling and Sealing**: The hot juice is poured into sterilized glass bottles, sealed immediately, and the caps are sterilized for 5 minutes to prevent contamination.
9. **Sterilization and Cooling**: The sealed bottles are sterilized in hot water at 85°C for 15 minutes, then cooled gradually by adding cold water in stages until the temperature reaches 35°C. The bottles are then labeled and prepared for packaging.
Product Characteristics:
The finished juice has a beautiful purple or light purple color, is clear and transparent, and has a distinct grapefruit-like flavor with a balanced sweet and sour taste. There may be some sediment or tartaric acid crystals after long storage, which is normal. The soluble solids content ranges from 15% to 18% (measured by refractometer), and the total acidity is between 0.4% and 1.0% (as tartaric acid).
Important Notes:
During processing, avoid contact with iron or copper metals to prevent discoloration. For lighter-colored grapes, cold-pressed juice is recommended to preserve the delicate flavor and aroma.
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