What Are The Characteristics of Plums Drying Equipment

Plum (especially the prune variety) drying equipment has several distinct features shaped by the fruit's high sugar and moisture content. The main goal is to dry the fruit evenly without causing surface hardening or scorching, while preserving its color and nutrients.

Core Drying Technologies & Features

1. Heat Pump Drying (Most Common for Quality & Energy Saving)

This is currently one of the most popular methods for plums. It uses a reverse Carnot principle to absorb heat from the air and transfer it into the drying chamber. Key features include:

Energy Efficiency: It can save significant energy compared to traditional electric heating. The specific moisture extraction rate (SMER) is notably higher than conventional dryers .

Optimal Temperature Range: Research suggests the optimum drying temperature for plums is around 70-80°C . Some commercial machines operate with a range of 15-80°C.

Batch Capacity: Typical industrial heat pump dryers for plums can handle 200 to 2500 kg per batch , or even larger custom capacities up to 10000 kg** .

Closed System: The drying process occurs in a sealed environment, ensuring hygiene and cleanliness .

2. Multi-Stage Humidity Control (Addressing Surface Crusting)

Plums have high sugar content, which can lead to a hard, impermeable "crust" forming on the surface if dried too quickly, trapping moisture inside. Advanced dryers address this:

Step-down Relative Humidity (RH) Drying: This technique starts with high humidity in the early stage to gently warm the fruit and allow internal moisture to move outward, minimizing the temperature gradient. Then, the RH is gradually reduced to increase the driving force for surface evaporation .

3. Hot Air Convection Systems

Traditional hot air dryers remain widely used and come in various forms:

Tunnel Dryers: Some designs use a tunnel at the inlet and outlet to prevent heat loss.

Key Specifications & Process Considerations

Temperature: Most processes operate between 50°C and 80°C. High-temperature drying (e.g., 65-80°C) is often used for initial surface moisture removal, followed by lower temperatures (50-60°C) for slow, thorough drying .

Drying Time: Depending on the method and desired final moisture, times can range from 18-30 hours for optimized processes to 36-48 hours for simpler systems .

Final Moisture Content: Commercial dried plums are typically dried down to about 20% moisture content (wet basis) .

Pretreatment: To significantly accelerate drying, pretreatments can reduce drying time from 42 hours to just **19 hours*

Equipment Design Considerations

Material: Equipment is typically made from SUS304 stainless steel to meet food hygiene standards .

Control Systems: Modern dryers use PLC and touch screen controls for precise temperature, humidity, and time management .

Multi-Functionality: Many industrial heat pump dryers Can dry various fruits

In summary, effective plum drying equipment focuses on precise, multi-stage control of temperature and humidity to prevent crusting, utilizes energy-efficient heat pump technology to ensure uniform drying without sticking.