Agro-processing machinery plays a vital role in horticulture by transforming raw agricultural produce into market-ready products, thereby enhancing value addition and reducing post-harvest losses. In Kenya, where horticultural exports contribute significantly to the economy, efficient operation of agro-processing equipment ensures quality products that meet both local and international standards. This chapter explores the different types of agro-processing machinery relevant to horticulture and their practical uses and operation techniques in Kenyan farms and agribusinesses.

6.1 Agro-processing machinery

Agro-processing machinery encompasses the wide range of equipment used to convert fresh horticultural produce into processed goods such as juices, dried fruits, jams, and packaged vegetables. Understanding the types of machinery available and their specific functions is essential for horticulture professionals to optimise production, maintain product quality, and ensure food safety in compliance with applicable food safety regulations.

6.1.1 Types of Agro-processing machinery

Agro-processing machinery varies depending on the type of horticultural product and the desired processed form. The machinery can be broadly grouped by the job it does on the farm: reducing size (mills and grinders), separating the edible part from its covering (shellers), removing moisture (dryers), and moving material between stages (elevator conveyors). Primary, secondary, specialised, and manual equipment for fresh produce is described after these five types.

6.1.1.1 Mills

A mill is a machine that breaks dry material into flour, meal, or coarse particles by impact, crushing, or shearing. On a horticultural farm, mills are used to turn dried cassava chips, dried sweet potato chips, dried bananas, and maize into flour that can be bagged and sold or mixed into composite flours. Choosing the right type of mill depends on the hardness and dryness of the material and on how fine the product must be.

The main types of mill are compared below.

Main parts and features of a mill:

• Hopper: Holds the material and feeds it into the milling chamber at a controlled rate. A feed gate prevents overloading the motor.
• Milling chamber: Contains the hammers, plates, rollers, or stones where size reduction takes place.
• Screen or plate gap: Controls the fineness of the product. A screen with small holes or a narrow plate gap gives fine flour, and a larger opening gives coarse meal.
• Drive unit: An electric motor, or a diesel or petrol engine, connected through a belt and pulleys. The pulley sizes decide the working speed.
• Outlet and collection: Delivers the milled product into a bag or container, often assisted by a blower that also removes dust.
• Guards: Cover belts, pulleys, and the feed opening so that the operator cannot touch moving parts.

6.1.1.2 Grinders

A grinder reduces material to a fine powder or paste, usually in smaller batches than a mill and with closer control over particle size. In horticulture, grinders are used for spices and herbs such as dried chillies, coriander seeds, turmeric, and ginger, and for making pastes such as groundnut butter or chilli paste. Because the product is often sold directly to consumers, grinders must be easy to clean to prevent flavour carry-over between batches.

Common types of grinder:

• Disc (attrition) grinder: Material passes between a fixed disc and a rotating disc with ridged faces. The gap between the discs is adjustable, so one machine can produce coarse or fine powder.
• Pin grinder: Rotating pins strike and shatter brittle dried material such as spices. It suits dry, low-oil products.
• Wet (stone) grinder: Rotating stones or rollers grind soaked or fresh material into a paste. It is used for pastes such as ginger-garlic or chilli paste.
• Burr grinder: Two serrated burrs crush seeds or beans to an even size. It is used for small-batch grinding of seeds and spices.
• Hand-operated grinder: A clamped grinder with a handle for very small quantities. It works where electricity is not available and costs little.

Features to check when selecting a grinder include the material of food-contact parts (stainless steel is easy to clean and does not taint the product), the adjustment of fineness, the rated capacity in kilograms per hour, and the power source.

6.1.1.3 Shellers

A sheller removes the edible seed or kernel from its pod, husk, cob, or shell. Shelling by hand is slow and tiring, whereas a sheller can handle many times more produce per hour with less damage when it is correctly adjusted. Examples on a horticultural farm are shelling dry maize from cobs, groundnuts from pods, and dry beans or peas from pods.

Types of sheller:

• Hand-held or hand-cranked maize sheller: The cob is pressed against a toothed wheel or drum and turned so that the kernels are stripped off. It suits small quantities and needs no fuel.
• Rotary drum (cylinder and concave) sheller: Cobs are fed into a rotating cylinder with spikes or rasp bars that rub the kernels loose against a curved concave. The cobs leave at one end and the grain falls through a grid.
• Groundnut sheller: Pods are rubbed or beaten against a perforated grid. The kernels fall through the holes while the broken shells are blown or sieved away. The hole size must match the pod size to avoid crushing the kernels.
• Bean and pea sheller (thresher-sheller): A beater drum breaks open dry pods, and a sieve and fan separate seed from pod material.
• Motorised sheller: Any of the above driven by an engine or electric motor for larger volumes.

Important performance points are the shelling efficiency (how much of the produce is fully shelled), the percentage of broken seed, and the cleanliness of the shelled product. Produce should be dry enough before shelling, because damp pods and cobs shell poorly and increase breakage.

6.1.1.4 Dryers

A dryer removes moisture from harvested produce so that it can be stored or processed without rotting or developing mould. Drying lowers the water content by passing warm, moving air over the produce, and the moving air carries the moisture away. Examples are drying sliced mangoes, bananas, and tomatoes for sale as dried fruit, and drying cassava chips or maize before milling or storage. The drying temperature must be matched to the product, because excessive heat hardens the outer surface and traps moisture inside, or spoils flavour and colour.

The main types of dryer are compared below.

Solar dryers use renewable energy and reduce dependence on fuel, which suits rural cooperatives and farms with unreliable electricity. Features common to most dryers are a way to control or monitor temperature, a way to control airflow through vents or fans, trays or racks that allow air to pass around every piece of produce, and food-grade surfaces that are easy to clean.

6.1.1.5 Elevator conveyors

An elevator conveyor is a machine that moves bulk produce from one level or station to another without manual carrying. On a farm processing line it can lift shelled grain to the top of a silo, carry dried chips from a dryer to a mill hopper, or move cleaned produce from a washing machine to a sorting table. Mechanical handling saves labour, speeds up the line, and reduces bruising and spillage.

Types of elevator and conveyor:

• Bucket elevator: Buckets fixed to a belt or chain scoop up the material at the bottom (the boot) and tip it out at the top (the head). It lifts grain, shelled groundnuts, and dried chips vertically.
• Screw (auger) conveyor: A rotating helical screw inside a tube or trough pushes dry material along, horizontally or at a slope. It is compact and useful for feeding hoppers.
• Belt conveyor: A continuous belt on rollers carries produce horizontally or up a gentle incline. A cleated belt keeps produce from rolling back, and it is common for carrying whole fruit and vegetables.
• Chain or slat conveyor: Slats or links driven by a chain move heavier items such as crates or sacks.
• Pneumatic conveyor: A stream of air carries light, dry, free-flowing material through pipes. It suits fine powders and light grains but needs more power.

Main parts of a bucket elevator are the boot with its tail pulley, the head with its drive pulley and motor, the belt or chain, the buckets, and the casing that encloses them. The casing and guards protect people from moving parts and also stop dust escaping.

Primary processing equipment for fresh produce

Primary processing involves initial preparation steps such as cleaning, sorting, and peeling. These machines prepare the raw produce for further processing.

• Washing Machines: Remove dirt, pesticide residues, and foreign matter from fruits and vegetables. For example, at a mango farm, washing machines reduce microbial contamination before pulping.
• Sorting and Grading Machines: Separate produce based on size, weight, or quality, ensuring uniformity for packaging or further processing.
• Peeling Machines: Mechanically remove skins from fruits like pineapples or potatoes, reducing manual labour and increasing throughput.
• Cutting and Slicing Machines: Prepare produce into uniform pieces for drying or cooking, such as slicing carrots for dehydrated snacks.
• De-stoning and De-seeding Machines: Remove seeds from fruits like avocados or passion fruits, facilitating pulp extraction.

Secondary processing equipment for fresh produce

Secondary processing machines convert the prepared raw materials into consumable products.

• Juicers and Pulp Extractors: Extract juice or pulp from fruits such as oranges and guavas, used in fruit juice production.
• Cookers and Pasteurisers: Heat products to eliminate pathogens and enzymes, improving safety and shelf stability, widely used in jam and sauce production.
• Mixers and Blenders: Combine ingredients uniformly, essential in making fruit jams, purees, and sauces.
• Packaging Machines: Automate filling, sealing, and labelling of processed products, ensuring hygiene and consistent presentation.

Specialised machinery

These machines address niche processing needs or emerging technologies in horticulture.

• Extruders: Produce snacks or dried products by forcing material through shaped dies, used in value-added vegetable snack production.
• Oil Extractors: Extract essential oils from herbs like rosemary or lemongrass, supporting diversification in horticultural enterprises.
• Cold Storage Units: Though not processing machines per se, they are critical for maintaining processed product quality before distribution.

Manual and semi-automatic equipment

In smallholder and emerging horticultural enterprises, manual or semi-automatic machines provide cost-effective options.

• Hand-operated Juicers: Suitable for small volumes, common in rural fruit processing groups.
• Manual Peeling and Cutting Tools: Useful where electricity is unreliable, ensuring continued processing during outages.

Chapter Summary

This chapter provides a comprehensive overview of agro-processing machinery, beginning with the identification and classification of various types such as mills, grinders, shellers, dryers, and elevator conveyors. It explores the specific uses and operational procedures for each category of machinery, emphasizing their roles in enhancing farm productivity. The chapter further addresses the critical aspects of maintenance, including routine servicing, timely repairs, and appropriate storage practices to ensure longevity and optimal performance of the equipment. Detailed guidance is given on the operation of each type of machinery within a farm setting, highlighting practical steps to maximize efficiency and safety. Additionally, the chapter discusses general resources, materials, and supplies essential for the upkeep of mills, grinders, shellers, and dryers. This holistic approach equips learners with the knowledge to effectively manage agro-processing machinery, ensuring sustainable farm operations.