**Abstract**

The major reasons for developing mechanical technologies for olive harvesting are the chronic shortage of workers for manual harvesting and increasing labor costs. To enable these technologies to operate, new table olive cultivars suitable for mechanical harvesting are necessary. The two major factors required for the shift from manual to mechanical harvesting of table olives are improved harvesting efficiency and prevention of fruit injury. Improved harvesting efficiency requires suitable pretreatment to enable fruit abscission with minimal defoliation, even when the harvesting is performed by a trunk shaker. The second requirement is prevention of external fruit color change or browning as a result of fruit injury, by development of olive cultivars with firm skin and higher resistance to the bruising caused by mechanical harvesting. This genetic adaptation to mechanical harvesting must be accompanied by efficient post-harvest processing of the olives. In this chapter, we will review the published studies regarding mechanical harvest of table olives, and attempt to identify the main issues, which still need to be studied in order to facilitate the transition from hand to mechanical harvest of table olives.

**Keywords:** table olive, mechanical harvest, olive cultivars, fruit injury, trunk shaker, harvester

## **1. Introduction**

Table olives (*Olea europaea* L.) have been consumed by populations surrounding the Mediterranean basin, as long as 7000 years ago [1]. Their consumption has expanded to many other countries due to the increasing popularity of the Mediterranean diet [2]. The World Catalog of Olive Cultivars reports about 2500 olive varieties, and their selected use–for oil, table or both, is determined by given parameters [3]. Of these, table olives account for an annual worldwide production of close to 3 million tons.

In general, varieties of table olives are mostly low in oil content, medium to large in size, with flesh-to-pit ratios higher than 4:1 and appropriate texture as set by the International Olive Oil Council (IOC) [4]. The olive trees produce drupes consisting of an epidermis and a soft mesocarp surrounding a stone containing the seed [5]. The epidermis (1.5–3% of the total weight), is constituted mainly of cellulose and cutin, its main function being to protect against external infestations or injury [6]. The olive mesocarp constitutes 70–90% of the fruit weight, the stone accounts for another 5–30%, and the seed is about 1–3% of the fruit, by weight [7].

The five major producers of table olives today are (listed in alphabetic order) Algeria, Egypt, Greece, Spain and Turkey [4]. According to the IOC 2019 report, world table olive production exceeded 2.9 million tons for the season of 2017/2018 [8]. Production is increasing in other regions, such as South America, Australia, and the Middle East with Italy and Portugal also being major producers [9]. Israel has also developed several varieties of table olives, such as 'Kadeshon' and 'Lavee' [10]. However, these varieties play a minor role in the world market.

Classification of table olives is based on standards set by the International Olive Council in 2008 and reaffirmed in 2011 (COI/OT/MO/Doc. No 1. Method for the sensory analysis of table olives and Decision No DEC-18/99-V/2011 COI/OT/MO No 1/Rev. 2). Classification of table olives is based on the median Defect Predominantly Perceived (DPP). Four categories were designated: (1) Extra or Fancy: DPP ≤ 3; (2) First Choice or Select: 3 < DPP ≤ 4.5; (3) Second or Standard: 4.5 < DPP ≤7.0; (4) Olives that may not be sold as table olives: DPP > 7.0. Hardness, crunchiness and fibrousness have also been characterized in table olives [11]. Thus, it is important to be aware of the external characteristics of table olives, such as texture and appearance, their importance in the demand for table olives and their role in determining the price to be obtained in the marketplace.

For these reasons, table olives are traditionally harvested manually. It is interesting to note that despite being one of the oldest domesticated fruit crops in the world [1], table olives have benefitted from few technological innovations, especially in regard to harvesting [12]. Because their external appearance and texture are so important in their marketing appeal, special caution must be practiced at harvest. However, a chronic shortage of workers and high labor costs have prompted the need for other, more efficient and economic solutions. Mechanical harvesting methods practiced today are (1) trunk shaking, which can be applied simultaneously with rod beating; and (2) use of an overhead harvester. To promote harvest efficiency, application of an abscission agent should also be considered. Different cultivars may react differently to these mechanical and agronomical methods. In their research, Zipori et al. [13] compared the harvesting efficiency and final product quality of four cultivars of green table olive, 'Manzanillo', 'Hojiblanca', 'Souri', and 'Nabali Mouhassan', in response to manual versus trunk shaker harvesting.

When mechanical harvesting was supplemented by rod beating, harvesting efficiency reached 80–95%, similar to the efficiency of manual picking. However, harvesting efficiency of the trunk shaker without rod beating was significantly lower [13]. Interestingly, application of an abscission agent to accelerate fruit detachment and facilitate mechanical harvest, did not improve harvesting efficiency. Cultivar dependence was also observed: 'Hojiblanca', 'Souri' and 'Nabali Mouhassan' varieties showed similar final product quality using either method, while the quality of 'Manzanillo' olives harvested mechanically was inferior to those harvested manually.

The high sensitivity of table olives to damage caused by mechanical harvesting limits the suitability of this rather efficient method. An objective determination and quantification of the damage caused to table olives by mechanical harvesting may be obtained by digital image analysis. Investigation of fruit damage conducted on 'Manzanillo' table olives in Seville, Spain showed that mechanical harvesting with a trunk shaker led to a rate of bruising 12 times greater than that obtained by manual harvesting. About 60% of the damage to fruit was attributed to fruit-fruit abrasion, fruit-branch contact, and friction from the vibration of the fruit in the tree canopy during harvesting [14]. Most external bruising appeared within the first hour after harvesting.

#### *Table Olives: Toward Mechanical Harvesting DOI: http://dx.doi.org/10.5772/intechopen.102700*

Another recently developed harvesting technology is the New Pneumatic Harvester (NPH). Two oil cultivars ('Mari' and 'Yellow') were selected to evaluate the NPH system. Harvesting capacity and efficiency, leaf loss and fruit damage were measured. Results showed that the NPH harvested 92% of olive fruits. The percent of leaf loss during the harvesting process was 2.55%. The collector system reduced the level of damaged fruit from 61–25% in both tested cultivars [15].

The mean value of harvesting efficiency with trunk shakers is 72–74%, when applied without the addition of rod beating or abscission agents [16, 17]. In order to achieve harvesting efficiency greater than 85%, tree trunk vibration parameters were set above an acceleration value of 183.4 m/s2 , and at a frequency of 28.1 Hz. Although increasing the trunk acceleration improved harvesting efficiency, it led to an increase in damage to the harvested fruit 3.5 times greater than the damage caused by manual harvesting [16]. This technique also caused damage to the tree trunk [17].

Olive orchards should be specially prepared for this technology before its application. Ferguson and Garcia [12] studied the effects of pruning on fruit yield that was mechanically harvested. They compared the yield achieved by mechanical harvesting after two different pruning methods - mechanical pruning during six consequential years to that of manual pruning. They reported that use of mechanical pruning resulted in a harvest of 92% of the total yield on the trees where only 81% was harvested from trees that had been hand-pruned. There were no significant differences in the percentage of fruit yield and fruit size as a result of the different pruning treatments. They concluded that the use of mechanical pruning does not decrease average annual yields. These results suggest that in addition to the use of mechanical harvesting, pruning can also be done mechanically without lowering the yield of the tree, thus reducing the management costs of the trees "trained" and adapted for.

Mechanical harvesting can also be carried out by use of an overhead grape harvester. To use this device, the olive grove must be planted with suitable varieties with rows aligned specially for the harvester. New grove designs and management practices such as super-high-density groves which are used in oil olive production should be developed as an option for mechanical harvesting of table olives. In 2012, two table olive cultivars, 'Manzanillo de Sevilla' and 'Manzanillo Cacereña', were harvested in a 5-year-old super-high-density grove (1975 trees/ha) after being planted in continuous hedgerows (≈10,000 and 18,000 kg·ha−1, respectively). The differences between manual and mechanical harvesting (using a grape straddle harvester), in time, efficiency, and fruit quality were assessed [18]. The average harvest time per hectare with a grape straddle harvester was less than 1.7 hours compared with minimum of 576 man-hours/hectare for manual harvest. Fruit removal efficiency was high in both cases (98%). The mechanically harvested olives had a very high rate of bruised fruits (>90%). The severity of the damage was greater in 'Manzanillo de Sevilla' than in 'Manzanillo Cacereña'. After Spanish-style green processing, however, the proportion of bruised fruits was below 3% for each cultivar. Mechanically harvested fruits showed a significantly higher proportion of cutting (18%), a type of damage that may take place during harvesting, and reduced firmness than those harvested manually [18].
