A drying method suitable for mass production of dried lychee

Abstract

This invention provides a drying method suitable for large-scale production of dried lychees, belonging to the field of agricultural product processing technology. The method includes a three-stage drying process and corresponding temporary storage: after sorting and traying the fresh fruit, it undergoes blanching at 70℃ for 36 hours, followed by a second drying at 60℃ for 24 hours, and a third drying at 50℃ for 12 hours. After each drying stage, the fruit can be temporarily stored or stored long-term in a cold storage at -5℃ to 5℃. The parameters of this invention are derived from large-scale factory production practices. Differentiated dehumidification rhythms achieve gradient moisture extraction, resulting in a finished product yield ≥95%, a fruit shell shriveling rate ≤5%, and adaptability to daily production capacity requirements. Biomass heating energy consumption is reduced by 20%, and the product storage period exceeds 12 months, significantly extending the storage time compared to traditional room temperature storage, greatly reducing the risk of product spoilage and improving supply chain stability.

Description

Technical Field

[0001] This invention relates to the field of agricultural product processing technology, and more specifically, to a drying method suitable for large-scale production of dried lychees. Background Technology

[0002] Lychee is a characteristic tropical fruit of southern my country. Its flesh is rich in vitamins, sugars, and minerals, with a uniquely sweet flavor. However, lychee fruits have a water content exceeding 80%, and their rapid respiration after harvesting means they can only be kept fresh for 3-5 days at room temperature, easily turning brown and rotting, resulting in a post-harvest loss rate exceeding 30%. Dried lychee, as an important deep-processed product, significantly extends the storage period through dehydration while retaining the core nutrients of the lychee. It is a key way to solve post-harvest losses and increase the added value of the lychee industry, leading to a continuously growing market demand.

[0003] Currently, the drying and processing of dried lychees mainly relies on traditional, rudimentary drying methods and simple hot air drying techniques, which have many shortcomings that make them difficult to adapt to industrial production. Traditional drying methods often use open flames in drying rooms, making precise temperature control difficult. This can easily lead to localized overheating and charring of the fruit flesh, while uneven heating of the fruit shells results in large areas of shriveling and cracking. The yield rate is generally below 80%, and the rate of shriveled fruit shells exceeds 20%. Some simple hot air drying methods use a single high-temperature drying process of 65-70℃ for an extended period. This causes rapid evaporation and shrinkage of surface moisture, blocking the channels for water to drain from the flesh, resulting in a "dry outside, wet inside" situation. This makes the fruit extremely susceptible to moisture absorption and mold during storage, and the excessive shrinkage of the fruit shells causes them to lose elasticity, significantly reducing their commercial value.

[0004] Existing drying processes largely rely on manual operation and lack standardized procedures. Traditional drying rooms often use stacked lychees, causing uneven heating due to the fruit pressing against each other. A single batch can only process a few hundred kilograms, which cannot meet the daily production capacity requirements of large processing plants. Furthermore, drying parameters depend on the operator's experience for adjustment, resulting in significant differences in the dryness and appearance of different batches of finished products, making it difficult to maintain a stable market supply quality.

[0005] Traditional drying methods mostly use firewood and coal as fuel, which results in incomplete combustion and produces a large amount of smoke and dust, failing to meet environmental emission standards. Furthermore, the heat energy utilization rate is less than 30%, leading to serious energy waste. Some small processing plants use electric heating for drying, which produces less pollution, but the cost is 2 to 3 times that of biomass fuel, significantly reducing processing profits and making it difficult to scale up.

[0006] Existing drying processes do not address the gradient of moisture release in lychees, resulting in significant fluctuations in the moisture content of the finished product. Furthermore, the lack of standardized post-drying storage procedures makes semi-finished products prone to rehydration at room temperature, limiting their storage life to only 3-6 months. Frequent turning and maintenance are necessary, increasing labor costs and increasing the risk of secondary contamination, making it difficult to meet the market demands for long-distance transportation and cross-seasonal sales. Therefore, a drying method suitable for large-scale production of dried lychees is proposed. Summary of the Invention

[0007] The purpose of this invention is to address the problems identified in the existing background technology. To achieve the above-mentioned objective, this invention provides the following technical solution: a drying method suitable for large-scale production of dried lychees, comprising the following steps: Step 1: Place the sorted fresh lychees individually on breathable trays, place the trays on movable supports, and then move them into a 70℃ constant temperature drying workshop for 36 hours to complete the blanching process. The drying workshop generates heat energy through a biomass burner, which is then evenly ventilated by a large fan. The dehumidifying fan at the top of the workshop runs in a cycle of 5 minutes on and 1 minute off. After blanching, the lychees are cooled to room temperature and then temporarily stored in a cold storage at -5℃ to 5℃. Step 2: Transfer the lychees temporarily stored in Step 1 to a 60℃ constant temperature drying workshop and dry for 24 hours to complete the secondary drying; the heat supply and air supply method of the drying workshop is the same as in Step 1, and the dehumidifying fan runs in a cycle of 5 minutes on and 2 minutes off; after the secondary drying, the lychees are cooled to room temperature and then temporarily stored in a cold storage at -5℃ to 5℃. Step 3: Transfer the lychees temporarily stored in Step 2 to a 50℃ constant temperature drying workshop and dry them for 12 hours to complete three drying cycles; the heat supply, air supply method and dehumidification mode of the drying workshop are the same as in Step 2; after the lychees have been dried three times, let them cool to room temperature and then transfer them to a cold storage at -5℃~5℃ for long-term storage.

[0008] As a preferred technical solution of the present invention, the fresh lychees mentioned in step 1 are lychee fruits with uniform maturity, free from pests and diseases and mechanical damage, and the fruit stems and surface impurities are removed.

[0009] As a preferred technical solution of the present invention, the lychee fruits on the breathable tray in step 1 do not come into contact with each other, ensuring uniform heating during the drying process.

[0010] As a preferred technical solution of the present invention, the movable support described in steps 1, 2 and 3 is used for batch loading of pallets to realize convenient transfer of lychees between different drying workshops and cold storage.

[0011] As a preferred technical solution of the present invention, the temporary storage time in step 1 shall not exceed 7 days, and the temporary storage time in step 2 shall not exceed 7 days.

[0012] As a preferred technical solution of the present invention, the long-term storage period in step 3 is not less than 12 months.

[0013] As a preferred technical solution of the present invention, the constant temperature error of the drying workshop is controlled within ±2℃ to ensure stable drying temperature.

[0014] As a preferred technical solution of the present invention, the cooling process described in steps 1, 2 and 3 is natural cooling to avoid forced cooling that could cause the lychee shell to crack.

[0015] As a preferred technical solution of the present invention, the biomass burner uses biomass pellets such as straw and wood chips as fuel to achieve energy-saving and environmentally friendly heating.

[0016] As a preferred technical solution of the present invention, the three-stage stepped cooling and drying process from step 1 to step 3 ensures that the yield of dried lychees is not less than 95% and the rate of shriveled fruit shells is not more than 5%.

[0017] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention employs a stepped cooling and segmented drying design. In the first stage, a high-temperature blanching process at 70℃ rapidly deactivates the fruit's oxidizing enzymes, preventing browning of the pulp. Simultaneously, high-frequency short-duration dehumidification (5 minutes of operation followed by 1 minute of rest) quickly removes surface moisture, preventing premature shrinkage and water retention in the fruit shell. In the second and third stages, the temperature is gradually reduced to 60℃ and 50℃ respectively, with an adjusted dehumidification rhythm, allowing for slow extraction of moisture from the pulp, reducing the shrinkage difference between the shell and the pulp that leads to shriveling and cracking. Verified by large-scale processing plants, this method achieves a lychee drying yield of over 95%, an improvement of 15%–20% compared to traditional drying methods. The shriveling rate of the fruit shell is reduced to below 5%, and the finished fruit shell retains its natural wrinkled shape, while the pulp remains tender and plump, maximizing the preservation of the original flavor and nutrients of the lychee.

[0018] This invention employs a movable support frame combined with a single tray for loading, enabling the lychees to be evenly layered. A single support frame can hold hundreds of kilograms of lychee raw materials in batches. Combined with an independent constant-temperature drying workshop, multiple batches can be dried simultaneously, processing several tons of lychee raw materials at a time, increasing daily production capacity by more than 2 times compared to traditional processes. Furthermore, a -5℃ to 5℃ cold storage facility is provided after each stage of drying. This buffers the production pace, prevents congestion in the drying workshop, and prevents semi-finished products from becoming damp again. It flexibly adapts to large-scale continuous production processes in factories, reducing labor intensity and improving production efficiency.

[0019] All drying parameters in this invention are derived from the summary and optimization of large-scale production data from large processing plants. The combination of stepped temperatures and durations (70℃ / 36h, 60℃ / 24h, 50℃ / 12h) and differentiated dehumidification circulation modes, designed specifically for the water content of lychees, avoids parameter fluctuations caused by reliance on experience in traditional processes. Standardized operating procedures ensure consistent quality for each batch of dried lychees, solving the problems of uneven drying and significant differences in appearance in traditional drying methods, thus enhancing the product's market competitiveness.

[0020] This invention uses a biomass burner as a heat source, reducing carbon emissions by more than 30% compared to traditional coal and oil heating methods, and also lowering fuel costs. Simultaneously, through a precise dehumidification mode design, it avoids energy waste caused by continuous operation of the dehumidification fan. Combined with segmented drying temperature gradient settings, it reduces heat loss, resulting in an overall drying energy consumption reduction of approximately 20% compared to traditional processes, effectively compressing factory production costs.

[0021] After three stages of drying, the moisture content of the dried lychees remains stable within a safe storage range of 18% to 22%. Combined with long-term storage in a cold storage at -5℃ to 5℃, it can inhibit the growth of microorganisms and enzyme activity, and the storage period can reach more than 12 months, which is more than 6 months longer than traditional room temperature storage. This significantly reduces the risk of product expiration and loss and improves the stability of the supply chain. Attached Figure Description Figure 1 A data block diagram of drying process parameters provided by the present invention; Figure 2 A flowchart illustrating the raw materials and tray arrangement provided by this invention; Figure 3 A feature block diagram of the device and transfer system provided by the present invention; Figure 4 A flowchart illustrating the process effects and quality indicators provided by this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are specific implementations of the present invention and are not limited to all embodiments.

[0023] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely illustrates some embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0024] It should be noted that, in the absence of conflict, the embodiments and features and technical solutions in the embodiments of the present invention can be combined with each other. It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] Example 1: A drying method suitable for mass production of dried lychees, comprising the following steps: Step 1: The sorted fresh lychees are individually placed on breathable trays, the trays are placed on movable supports and then moved into a 70°C constant temperature drying workshop, where they are dried for 36 hours to complete the blanching process; the drying workshop generates heat energy through a biomass burner, which is evenly ventilated by a large fan, and the dehumidifying fan at the top of the workshop runs in a cycle of 5 minutes on and 1 minute off; after blanching, the lychees are cooled to room temperature and then temporarily stored in a cold storage at -5°C to 5°C; Step 2: Transfer the lychees temporarily stored in Step 1 to a 60℃ constant temperature drying workshop and dry for 24 hours to complete the secondary drying. The heat supply and air supply method of the drying workshop are the same as in Step 1. The dehumidifying fan runs in a cycle of 5 minutes on and 2 minutes off. After the secondary drying, let the lychees cool to room temperature and then transfer them to a cold storage at -5℃ to 5℃ for temporary storage. Step 3: Transfer the lychees temporarily stored in Step 2 to a 50℃ constant temperature drying room and dry them for 12 hours to complete three drying cycles. The heat supply, air supply method and dehumidification mode of the drying room are the same as in Step 2. After the lychees have been dried three times, let them cool to room temperature and then transfer them to a cold storage at -5℃ to 5℃ for long-term storage.

[0026] In step 1, the fresh lychees are those that are uniformly ripe, free from pests and diseases and mechanical damage, and the fruit stems and surface impurities are removed.

[0027] In step 1, the lychee fruits on the breathable trays do not come into contact with each other, ensuring even heating during the drying process.

[0028] The movable supports in steps 1, 2 and 3 are used for bulk loading of pallets, enabling convenient transfer of lychees between different drying workshops and cold storage facilities.

[0029] The temporary storage time in step 1 shall not exceed 7 days, and the temporary storage time in step 2 shall not exceed 7 days.

[0030] In step 3, the long-term storage period should be no less than 12 months.

[0031] The temperature error in the drying workshop is controlled within ±2℃ to ensure stable drying temperature.

[0032] The cooling process in steps 1, 2 and 3 is to allow the fruit to cool naturally to avoid forced cooling that could cause the lychee shells to crack.

[0033] Biomass burners use biomass pellets such as straw and wood chips as fuel to achieve energy-saving and environmentally friendly heating.

[0034] By using a three-stage cooling and drying process from step 1 to step 3, the yield of dried lychees is no less than 95%, and the rate of shriveled fruit shells is no more than 5%.

[0035] Example 2: A drying method suitable for large-scale production of dried lychees, specifically a standardized large-scale drying example for Guiwei lychees. This example uses 10 tons of fresh Guiwei lychees from a lychee processing plant as raw material: First stage: Blanching and drying: Guiwei lychees harvested within 12 hours are manually sorted to remove diseased, pest-infested, and damaged fruit. They are then individually placed on perforated plastic trays, with 2 kg of lychees evenly distributed per tray. 5000 trays are placed in batches on 100 movable supports and moved into a 70℃ constant temperature drying workshop. A biomass burner is started for heating, and large fans in the workshop circulate air to maintain a uniform temperature. The top dehumidifier operates on a 5-minute cycle, stopping for 1 minute, for a continuous drying period of 36 hours. After blanching, the lychees are transferred with the trays to a -5℃ to 5℃ cold storage for temporary storage, producing a total of 7.2 tons of blanched semi-finished product.

[0036] The second stage of secondary drying: The blanched semi-finished products temporarily stored in the cold storage were transferred in batches to a 60℃ constant temperature drying workshop. The biomass burner maintained stable heating, the large fan continuously circulated air, and the dehumidifying fan operated in a cycle of running for 5 minutes and stopping for 2 minutes. After drying for 24 hours, the products were transferred to the cold storage for temporary storage, resulting in 5.1 tons of secondary dried semi-finished products.

[0037] The third stage involved three drying processes: the semi-finished products from the second drying stage were transferred in batches to a 50℃ constant-temperature drying workshop to maintain a stable temperature. The dehumidification cycle was the same as in the second stage. After drying for 12 hours, the products were removed, cooled, and then stored in a cold storage for long-term preservation, ultimately yielding 3.8 tons of finished dried lychees. Testing showed a yield rate of 96.2%, a shell shriveling rate of 3.1%, a pulp integrity rate of 97.5%, and a moisture content of 20.3%, meeting the first-grade dried lychee quality standards.

[0038] Example 3: A drying method suitable for large-scale production of dried lychees, using Fei Zi Xiao lychees in a staggered production process: This example uses Fei Zi Xiao lychees as raw material and adopts a staggered drying process: First stage: staggered blanching: 15 tons of fresh fruit are processed in 3 batches. The first batch of 5 tons of fresh fruit is placed on trays and moved into a 70℃ drying workshop. After drying for 36 hours according to the process in Example 1, it is moved into a cold storage for temporary storage. 12 hours after the first blanching starts, the second batch of 5 tons of fresh fruit enters the blanching process. 12 hours after the second batch starts, the third batch of 5 tons of fresh fruit enters the blanching process. Through staggered scheduling, the drying workshop is able to operate at full capacity, producing a total of 10.8 tons of blanched semi-finished products.

[0039] The second stage of drying: After the first batch of blanched semi-finished products were temporarily stored for 24 hours, they were moved into a 60℃ drying workshop for secondary drying. Simultaneously, 12 hours after the start of the second drying of the first batch, the second batch of blanched semi-finished products entered the second drying process, and the third batch of blanched semi-finished products followed 12 hours later, maintaining continuous operation in the workshop, and finally obtaining 7.7 tons of secondary dried semi-finished products.

[0040] The third stage involves batch drying: 7.7 tons of semi-finished product from the second drying process are transferred in two batches to a 50℃ drying workshop, where each batch is dried for 12 hours, ultimately yielding 3.0 tons of finished dried lychees. Under this model, the workshop's daily drying capacity increases to 4.5 tons, a 40% increase in efficiency compared to single-batch production, a finished product rate of 94.7%, a shell shriveling rate of 4.2%, and a storage period of up to 13 months, meeting the demand for large-volume orders from e-commerce platforms.

[0041] The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described herein. Although the present invention has been described in detail with reference to the above embodiments, the present invention is not limited to the specific embodiments described above. Therefore, any modifications or equivalent substitutions to the present invention, as well as all technical solutions and improvements that do not depart from the spirit and scope of the invention, are covered within the scope of the claims of the present invention.

Claims

1. A drying method suitable for large-scale production of dried lychees, characterized in that, Includes the following steps: Step 1: Place the sorted fresh lychees individually on breathable trays, place the trays on movable supports, and then move them into a 70℃ constant temperature drying workshop for 36 hours to complete the blanching process. The drying workshop generates heat energy through a biomass burner, which is then evenly ventilated by a large fan. The dehumidifying fan at the top of the workshop runs in a cycle of 5 minutes on and 1 minute off. After blanching, the lychees are cooled to room temperature and then temporarily stored in a cold storage at -5℃ to 5℃. Step 2: Transfer the lychees temporarily stored in Step 1 to a 60℃ constant temperature drying workshop and dry for 24 hours to complete the secondary drying; the heat supply and air supply method of the drying workshop is the same as in Step 1, and the dehumidifying fan runs in a cycle of 5 minutes on and 2 minutes off; after the secondary drying, the lychees are cooled to room temperature and then temporarily stored in a cold storage at -5℃ to 5℃. Step 3: Transfer the lychees temporarily stored in Step 2 to a 50℃ constant temperature drying workshop and dry them for 12 hours to complete three drying cycles; the heat supply, air supply method and dehumidification mode of the drying workshop are the same as in Step 2; after the lychees have been dried three times, let them cool to room temperature and then transfer them to a cold storage at -5℃~5℃ for long-term storage.

2. The drying method for mass production of dried lychees according to claim 1, characterized in that, The fresh lychees mentioned in step 1 are lychee fruits that are uniformly mature, free from pests and diseases and mechanical damage, and whose stems and surface impurities have been removed.

3. The drying method for mass production of dried lychees according to claim 1, characterized in that, In step 1, the lychee fruits on the breathable tray do not come into contact with each other, ensuring uniform heating during the drying process.

4. The drying method for mass production of dried lychees according to claim 1, characterized in that, The movable supports described in steps 1, 2, and 3 are used for bulk loading of pallets, enabling convenient transfer of lychees between different drying workshops and cold storage facilities.

5. The drying method for mass production of dried lychees according to claim 1, characterized in that, The temporary storage time in step 1 shall not exceed 7 days, and the temporary storage time in step 2 shall not exceed 7 days.

6. The drying method for mass production of dried lychees according to claim 1, characterized in that, The long-term preservation period mentioned in step 3 shall not be less than 12 months.

7. The drying method for mass production of dried lychees according to claim 1, characterized in that, The temperature error in the drying workshop is controlled within ±2℃ to ensure stable drying temperature.

8. The drying method for mass production of dried lychees according to claim 1, characterized in that, The cooling process described in steps 1, 2, and 3 is natural cooling to avoid forced cooling that could cause the lychee shells to crack.

9. The drying method for mass production of dried lychees according to claim 1, characterized in that, The biomass burner uses biomass pellets such as straw and wood chips as fuel to achieve energy-saving and environmentally friendly heating.

10. The drying method for mass production of dried lychees according to claim 1, characterized in that, By using a three-stage cooling and drying process from step 1 to step 3, the yield of dried lychees is no less than 95%, and the rate of shriveled fruit shells is no more than 5%.

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