The inspection table is the simplest solution for blueberry sorting. The fruit moves slowly along a belt while operators – positioned on both sides of the table – manually remove defects. In this way, it is possible to sort out soft, damaged or unripe fruit, as well as any contaminants. The inspection table requires no significant capital investment or complex servicing, and can operate independently or as a complement to a blueberry packing line equipped with other sorting machines.
The greatest weakness of the table is its dependence on the human factor. The effectiveness and efficiency of the inspection depends directly on the number of workers per shift, their experience and concentration – which naturally declines over the course of a long shift. The table only allows the elimination of defects visible to the naked eye: discolouration, mould and obvious mechanical damage, meaning sorting effectiveness is lower than with machine-based sorting. At high volumes, labour costs rise quickly and sorting quality levels drop.
The blueberry inspection table works best in small farms, at lower throughput levels, or as a final verification stage after mechanical or optical sorting – particularly later in the season, when fruit quality naturally declines and requires greater attention.
Grading blueberries by size is a fundamental sorting stage in most packing facilities. Two main types of equipment are available: hole calibrator and belt calibrator. Both mechanically separate fruits by diameter, but differ in construction and – consequently – in the way fruit passes through the machine.
The hole calibrator is one of the simplest and most affordable solutions. The fruit moves along a belt with holes of a defined diameter – smaller berries (those not meeting the client’s criteria) fall through the holes, while larger ones are conveyed further. The machine has few moving parts, is easy to operate and inexpensive to maintain. It works well in smaller farms or wherever low investment cost and simplicity are the priority. A potential drawback is fruit becoming lodged in the holes – particularly with irregular shapes or high product moisture levels.
The belt calibrator operates on a similar principle, but thanks to its adjustable-gap belt transport system, it treats the fruit more gently. The blueberry moves smoothly, without large drops, which reduces bloom abrasion and the risk of micro-damage. The design is straightforward and throughput is high relative to the machine’s size.
A shared limitation of both calibrators is the absence of fruit quality assessment. These calibrators sort blueberries solely by size criteria, without checking colour, firmness or defects.
The calibrators work well as pre-sorting equipment ahead of a more advanced machine. Another solution suitable as a pre-sorting device is the cleaning blower. The machine effectively removes leaves, stems, dried flowers and undersized fruit. It is an extremely useful machine for mechanical harvesting, as it allows unwanted material collected in the field to be screened out. The blower is gentle on the fruit and easy to service, takes up little space, and offers adjustable blowing intensity, giving users control over the sorting outcome.
The limitation of the blower is that it cannot detect fruit that fails to meet colour or firmness criteria. In general, the cleaning blower is not suitable as the sole sorting device in a line. However, it works well as the first of several sorting stages.
An optical sorter uses cameras, lasers or optical sensors to assess fruit quality on the move. The best models feature dual 2K cameras and provide RGB and near-infrared analysis. Unlike a grader, its purpose is not to divide fruit into grades, but to quickly and effectively remove fruit that fails to meet requirements. The machine analyses colour, firmness and size, and some models also detect defects such as mould or so-called collapse. Rejection is typically carried out by a jet of compressed air.
The key advantages of optical sorters are above all their speed of operation and compact dimensions compared to graders. They are simpler to operate, less expensive to maintain and generally easier to clean on a daily basis. Some models detect defects invisible to the naked eye, including assessment of the fruit’s interior.
The limitations include lower grading precision compared to graders and the need to regularly adjust settings to suit a specific batch of fruit. Most optical sorters offer several rejection channels (e.g. separate ones for firmness and colour), but do not allow for such detailed grade separation as a grader. This solution is intended primarily for producers who want to quickly and efficiently eliminate product that does not meet the buyer’s criteria, rather than precisely dividing the harvest into premium fractions. A good optical blueberry sorter is the best solution in terms of the ratio of sorting quality to machine price, floor space occupied in the packing facility, and the time required for machine operation.
A grader is the most advanced machine for blueberry sorting. The machine assesses fruit in terms of size, colour, firmness and defects, then separates it into several streams according to defined quality grades. The cameras typically take several dozen photographs of each blueberry, while guide rollers rotate the fruit so that the system can see it from all sides. Advanced optics ensure high classification accuracy.
This precision comes at a price. Graders are by far the most expensive solution in this comparison. However, the financial barrier is not the only drawback of investing in this advanced blueberry sorter. Graders take up a great deal of space – the sorting machines themselves often fill the entire length of the facility. The machines have many moving parts, which translates into higher servicing and maintenance costs. The long path the fruit must travel increases the risk of bloom abrasion and may shorten shelf life. Thoroughly cleaning a grader is an operation that can take a full day’s work for several people. In addition, directing fruit onto a specific lane (most commonly using compressed air) carries a risk of mechanical damage to fruit that has just been classified as a premium product.
A grader makes economic sense primarily when a producer sells to buyers who differentiate price according to quality grade (e.g. for export and the local market simultaneously) and when production volume justifies the high investment and maintenance costs.
Choosing the right sorting method requires taking several factors into account. These are above all production volume, fruit buyers, available floor space in the packing facility and, of course, the investor’s budget. Small farms often function well with an inspection table and a grader. Producers focused on a uniform product without precise grade classification turn to optical sorters. Graders are an investment for companies that genuinely benefit from dividing fruit into premium fractions and have buyers who pay more for those fractions. In practice, many packing facilities use a combination of different systems that together deliver a satisfactory level of fruit sorting – a belt grader as a preliminary stage, an optical sorter to eliminate defective fruit, and an inspection table as a final verification step. In such a configuration, each machine does what it does best. Combining several smaller machines allows for flexible design of the packing line, tailored to the dimensions of the facility and the investor’s expectations.
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