Design and Development of a Black Tea Rolling Machine Using the Orthodox Method

Background and Objectives
The Iranian tea industry, historically a significant agricultural sector, has faced progressive decline due to structural challenges, including technological obsolescence, monopolistic marketing systems, and limited accessibility of modern processing equipment for smallholder farmers. A critical bottleneck lies in the rolling stage, a decisive phase in Orthodox black tea production that directly influences leaf morphology, enzymatic oxidation, and final sensory quality. Existing industrial rolling machines predominantly require three-phase electricity, operate at large batch capacities (typically >100 kg), and are economically and technically inaccessible to rural households. Consequently, most small-scale growers are forced to sell raw green leaves at low prices, foregoing value addition and fair profit margins. This study was undertaken to design, simulate, fabricate, and evaluate a low-cost, single-phase, household-scale black tea rolling machine based on the Orthodox method, specifically tailored for rural tea farmers in northern Iran. The primary objectives were: (1) to enable on-farm processing using only 220 V single-phase grid power; (2) to replicate the leaf curling and minimal fragmentation characteristic of hand-rolled Orthodox tea; (3) to ensure structural integrity through finite element analysis; and (4) to quantify improvements in processing time, product quality, and economic feasibility compared to conventional methods.
Materials and Methods
The development process integrated field observation, mechanical design, computational simulation, and empirical validation. Initial design requirements were established through field visits to tea processing factories in Gilan Province and consultations with industry technicians and farmers. A prototype with a 10 kg batch capacity was conceptualized and modeled in SolidWorks 2022, incorporating key components: a rotating perforated cylinder (31 cm internal diameter, 45 cm height), a crank–rocker mechanism for variable rotational motion, a removable perforated pressure plate, and a modular steel frame. The drive system consisted of a 0.75 kW (1 HP) single-phase induction motor, a B-type industrial belt, and a worm gearbox (VF-N 62, ratio 1:19) to deliver sufficient torque at low speed. To calibrate processing parameters, three pressure levels (7.4 kg, 20.2 kg, and 45.9 kg) were applied via calibrated weights, corresponding to surface pressures of 100, 270, and 600 kg/m²—aligned with literature-reported optimal ranges for Orthodox rolling. Structural validation was performed using finite element analysis (FEA) in Abaqus 2021. Critical load-bearing components—gusset plates, the triangular crank-mounted plate, the cylinder support belt, and the pressure cylinder—were subjected to simulated operational loads (up to 51.3 kg force). Material properties of ST37 mild steel were assigned (density: 7850 kg/m³, Young’s modulus: 210 GPa, Poisson’s ratio: 0.3). Additionally, torque requirements were determined experimentally: the minimum force needed to initiate rotation of a 10 kg fresh tea load was measured using a pulley–weight system, yielding a baseline for motor selection. The final prototype was fabricated in the university workshop using standardized industrial practices, with safety features including an emergency stop and a protective crank guard.
Results
FEA results demonstrated exceptional structural robustness: the maximum von Mises stress was 9.233 MPa, maximum strain was 3.051 µε, and maximum displacement was 0.062 mm—all significantly below the yield strength of ST37 steel (235 MPa), ensuring a safety factor exceeding 25. Torque analysis confirmed that the selected motor and transmission system (delivering ~0.55 kgf·m at the crank) comfortably met the experimental requirement of 9.8 N per kg of fresh tea. Performance evaluation revealed that the machine successfully produced Orthodox-style rolled tea with uniform leaf curling, minimal fragmentation (<5%), and preserved leaf integrity, closely matching hand-rolled reference samples in appearance. Sensory assessments by trained panelists indicated that tea processed at 20.2 kg pressure (270 kg/m²) yielded the most desirable aroma and flavor profile—rich, floral, and less astringent than factory-processed CTC tea—aligning with findings from Heping et al. (2015). Crucially, the device reduced processing time from 40 minutes (manual rolling) to 25 minutes, while operating solely on 220 V single-phase electricity. Material optimization indicated that 4 mm steel sheets were optimal for gusset plates and the crank plate, 3 mm for the cylinder belt, and 2 mm for the pressure cylinder, with a 21 mm hole diameter ensuring secure fastening.
Conclusion
This study successfully developed and validated a practical, affordable, and technically sound household-scale Orthodox black tea rolling machine. By enabling smallholder farmers to process their own tea using accessible single-phase power, the device directly addresses core challenges of value retention, technological exclusion, and economic marginalization in Iran’s tea sector. The machine not only replicates traditional hand-rolling quality but also enhances efficiency and consistency. It represents a scalable model for decentralized, sustainable agro-processing that empowers rural producers, reduces post-harvest losses, and revitalizes local craftsmanship. Future work should focus on full automation, integration with withering and drying units, and quantitative chemical analysis (e.g., theaflavin content) to further validate quality enhancements. This innovation holds significant potential for replication in other tea-producing regions facing similar constraints.