The harvesting of small fruits is more and more mechanized

The red fruit market is in significant expansion, offering a wide variety of products with different organoleptic features. To make the collection more efficient, mechanical tools have been studied to facilitate and accelerate the harvesting. For American blueberries, industrial currants, and cranberries, differentiated mechanical means are available, while for strawberries, robotic systems are already on the market

Fruit juices, jams, and fresh consumption are the primary productive destinations of the so-called "soft fruits", whose cultivation is characterized by many species and varieties, which show quite different vegetative morphologies and planting patterns.

Small fruits can be classified according to their destination: Mainly for fresh consumption, such as strawberries, raspberries, and blueberries, or mainly for industrial processing, such as currants and cranberries. This differentiation inevitably reflects on harvesting methods: The species for fresh consumption are usually harvested by hand, as the mechanical collection could affect the integrity and, therefore, the shelf life. However, this solution is feasible for products intended for processing, as in this way, the collection time is drastically reduced, and the yield is maximized since the not perfect integrity of the product is not a problem.

 

Wild Blueberry and American Blueberry

The wild blueberry is a perennial plant that fruits between July and September; it is about 20 cm tall and produces small intense red berries rich in anthocyanins. This plant's structure and growth habits prevent mechanized harvesting of fruits; therefore, berries are harvested manually employing a rake or a comb. On the contrary, the American blueberry is a shrub/bushy plant whose height can far exceed 1 m. The American blueberry has white flesh and size 4-5 times bigger than wild blueberry. This last feature, together with the different plant conformation, enabled the mechanization of the harvesting, which is carried out by excavating, towed, or self-propelled machinery, which, similarly to grape harvesters, detaches the berries by shaking. The Polish company Jagoda JPS has developed the self-propelled Oskar 4WD Plus model with hydraulically operated shakers for optimal product selection from the leaves and any harvest residues. The manufacturer states the machine is suitable, in different configurations, for also harvesting rosehips, gooseberries, raspberries, etc. The Serbian BSK offers the Kokan 500s, a vineyard model that for harvesting berries uses a powerful air jet flow to shake the branches, causing the fruit to fall, with a productivity of 2-4 ha/day. The air jet action is more delicate than the mechanical shaking: In this way, it is possible to preserve the fruit's integrity, which, not being damaged, can be sold as a fresh product. After the blueberries are separated from the plant, they are directed onto several conveyor belts, which then carry them to a discharge chute, under which the storage boxes are placed.

 

Currants for industry

Currant is scarcely known in Italy, whereas it is more common in central-northern Europe, where it is widely used for making juices and compotes. In this case, it is not required that berries remain attached to the stalk, as it happens for the fresh product; on the contrary, it is helpful that fruits are free from foreign material to help the subsequent processing.

Currant plant has a shrubby shape and can be taller than 1.5 m; translucent fruits, very delicate and subject to damage, have a diameter of less than 1 cm, and are grouped in bunches of 10-20 berries each.

The mechanization of currant harvesting is similar to that of gooseberry and blueberry: A trailed or sometimes the self-propelled machine is used, very similar in principle to the grape harvester, which wraps the plants and using drums with flexible fingers removes the berries. A pair of conveyor belts underneath intercept the berries and convey them to trailers using rollers and an adjustable gooseneck duct. Other models, such as the Jagoda JPS Jarek 5, are placed sideways to the row: The bunches are detached from the branches by upper rotors equipped with flexible fingers and fall onto the conveyor belt that carries them to the machine's side, where another belt deposits them in boxes.

 

The cranberry

This fruit's leading producers are located in North America, Chile, and some Eastern European States. With a rather sour taste, cranberry is rarely sold for fresh consumption but is frequently used for making juices and jams, as dehydrated fruit, or as a base for dietary supplements. Fruits can be harvested dry or wet.

 In the first case, the product is picked for marketing as it is through facilitating tools for manual use equipped with a rotor pick-up with metal teeth. The harvested product is transported on conveyor belts to the rear of the vehicle.

 Conversely, wet harvesting is adopted for fruits to be used for industrial purposes. This processing is made possible by the particular cultivation procedures: In fact, cranberries grow on meadows that are land with high humidity, with a rather waterproof bottom. They are basically the equivalent of large tanks, bordered by natural banks up to one meter high.

 The first phase of the wet harvesting, which lasts one day and one night, foresees a night flooding of the tanks so that the following morning the crop is entirely submerged by 20-40 cm of water. At this point, a tractor equipped with a frame of elastic teeth like the harrow enters the field and shaking the submerged plants separates the berries from the plants. Because of the water's density, the plants' shaking is gentler than the traditional mechanical solution, which benefits the fruit quality. The detached berries float on the water, therefore, the next step is to group them in the middle of the tank, through a flow of air produced by a fan driven by the tractor. Meanwhile, a floating barrier is placed on the surface of the water with the tractor to concentrate the product at the point of collection, from where the berries are sucked by a pump that sends them to a device for selection from water and any other impurities, before being finally conveyed to a trailer.

               

Robotic strawberry harvesting

The fruit's non-uniform size and its high delicacy make the mechanized harvesting of strawberries in the open field particularly challenging. However, recently robotized solutions have emerged: The Spanish company Agrobot has developed an electrically operated straddler machine (Agrobot E-series) capable of harvesting fruit both in the open field and in greenhouses. The machine is equipped with 24 autonomous arms and can be set for different planting patterns, according to which the supports for the placement of the storage boxes of the harvested product are housed.

Through the mobility of the arms, the robot can pick strawberries from the ground up to 1-1.5 m in height, which is helpful in the case of substrate or hydroponic crops. The fruit selection is carried out through a series of optical and infrared sensors, which identify the products that have come to ripening. The arms pick the strawberry, cutting the stalk at 2-4 cm from the fruit, which is then gently placed inside the box. In this way, any direct contact with the fruiting body is avoided, thus reducing the possibility of product damage.