Over-the-Row Mechanical Harvest of Cider Apples (Malus domestica Borkh.)

Abstract

The single greatest annual production cost for an established cider apple (Malus domestica Borkh.) orchard is the labor required to hand harvest. Reducing harvest labor time may increase the appeal and profitability of growing cider apples. Over-the-row mechanical harvest of cider apples using a modified Oxbo-Korvan 930 was evaluated in northwestern Washington, USA, in 2021, 2022, and 2023 in a fully mature cider apple orchard that was planted in 2014–2016. Sixteen cider apple cultivars grafted on ‘Geneva 935’ rootstock were summer hedged between 7 and 20 July each year of this study. Plant growth regulators were applied before harvest to equalize the timing of harvest among cultivars. There were no differences among cultivars for the percent of apples captured by the Oxbo-Korvan 930 harvester for the 3 years of this study. Across all years and cultivars studied, 82% of fruit were captured by the harvester. There also were no differences among cultivars for the percentage of fruit left on the tree by the harvester (9% of fruit on average), nor in the percentage of fruit dropped on the ground during harvest (9% of fruit on average). The overall mean number of branches broken during mechanical harvest across all cultivars was 1.4 per tree, and there were no differences among cultivars. ‘Sweet Alford’ had high spur removal (26 removed per tree), but excluding this outlier, only 6 spurs on average were removed per tree for all other cultivars. Laceration to fruit during mechanical harvest were positively correlated with mean fruit weight and mean fruit diameter. The overall average time required to mechanically harvest one tree in this orchard (1.8 m in-row spacing, 1495 trees·ha⁻¹) was 5.3 s, averaging 2.9 s per row-meter traveled. The average time required to manually harvest one tree was 229 s (3.8 min). The juice quality of the mechanically harvested apples that were kept in cold storage and pressed within 42 d of harvest did not differ largely or consistently from juice quality of apples that were pressed within 3 d of harvest, except that sugars (measured through ºBrix and specific gravity) increased with storage time, as expected. Mechanical harvest using the modified Oxbo-Korvan 930 appears to be a labor-efficient and effective method of harvesting cider apples, and testing is needed in commercial orchards to evaluate its viability compared to other harvest technologies.

1. Introduction

The U.S. cider industry has expanded in the past two decades, increasing the demand for apple (Malus domestica Borkh.) cultivars with cider-making attributes such as high polyphenol content, acidity and sugars [1]. Due to the high cost of these specialty cider apples (USD 0.19 and USD 0.21 per kg in the Pacific Northwest in 2018 and 2019, respectively), many cidermakers purchase cull dessert apples or apple juice (USD 0.02 to USD 0.11 per kg) to make their ciders [2,3,4,5,6]. The high cost of cider apple fruit is largely due to their limited supply and high production costs.

Following establishment, the single greatest annual orchard production cost for cider apples is the labor required to hand harvest, which represents ~46% of annual variable costs [3,7]. Cider apples tend to be smaller than standard dessert fruit, thus can take up to four times longer to pick by hand [8]. Additionally, a large, capable, and consistent labor force can be difficult to recruit and house only for the brief harvest period [9], especially in areas where tree fruit are not abundantly grown such as western Washington, or when harvest dates for other crops conflict. Cider apples are suitable for mechanical harvest as they are pressed into juice soon after harvest; thus, cosmetic damage is not a critical quality concern. Further, bruising and damage of the fruit during mechanical harvest has minimal impact on juice quality [10].

In European cider apple orchards, shake-and-sweep mechanical harvest systems are the dominant harvest method. These systems utilize a hydraulic arm that grasps the tree trunk to “shake” apples onto the ground, then a machine comes along to “sweep” the apples off the ground. In this process, all apples that are on the orchard floor are picked up, including those of poor quality. In New York, mechanical harvest of cider apples using shake-and-sweep machinery was found to be more economical than hand harvest regardless of orchard scale [11]. However, shake-and-sweep harvest systems are not suitable for high density planting systems that utilize dwarfing rootstocks. Trunk shakers require a significant amount of time to use in high density orchards, and they can break smaller trees. The time required to shake trees in a 1-ha orchard of 2500 trees would be at least 41.5 h (~1 min per tree) [11]. Further, fruit needs to be collected from the ground, usually with a harvester that can cost USD 2000 to USD 200,000 depending on model and scale, and includes a mix of poor quality fruit [11]. Another consideration in the U.S. is that food safety requirements result in the restricted use of apples that have come in contact with the ground [12]. Smaller processors and/or cider producers may be willing to complete disclosure documentation and proper sanitation associated with processing ground-fallen fruit. However, larger processing facilities that mostly process handpicked apples may be less likely to accept ground-fallen fruit due to the sanitation required. A shake-and-catch mechanical harvester that prevents apple-to-ground contact would be more favorable in the U.S. This is especially important in Washington State, USA, where processing facilities are well-established for handpicked apples.

Over-the-row harvesters that remove and catch fruit have been utilized in olives, citrus, and processed berry and stone fruit production for many years. In 2014 and 2015, an over-the-row berry harvester (model OR0012; Littau Harvester, Lynden, WA, USA) was tested on low-trellised ‘Brown Snout’ cider apples in Washington State, USA, capturing 74% of apples on average with insignificant effects on juice quality [10,13]. The goal of the current study was to determine if an over-the-row modified Oxbo-Korvan 930 harvester (Oxbo International Co., Lynden, WA, USA) was suitable for harvesting cider apples in an orchard that was pruned through summer hedging to a fruiting wall system [14]. A further goal was to assess if mechanically harvested fruit could be cold-stored post-harvest without loss due to rot or decline in juice quality. The modified Oxbo-Korvan 930 harvester has the same drum, rod and conveyer belt system as the Littau harvester used in other studies; this study was to determine if the modified harvester height was suitable for cider apple harvest. Apple cultivars exhibit variation in stem length, stem abscission, fruit size and other factors that affect mechanical harvest efficiency [15]; thus, this study included 16 cider apples cultivars to assess the modified Oxbo-Korvan 930 over-the-row harvester.

2. Materials and Methods

2.1. Research Orchard

This experiment was carried out in a cider apple research orchard at Washington State University (WSU) Northwestern Washington Research and Extension Center (NWREC) (48°26′14.4″ N, 122°23′40.7″ W), located near Mount Vernon, WA, USA. The 0.35-ha cider apple research orchard was planted in 2014 and included two replicates of 65 cultivars in a randomized complete block design with three trees per plot. Trees were spaced 1.8 m apart in-row, with 3.7 m between rows (605 trees·acre⁻¹). Trees were grafted to ‘Geneva 935’ (Malus hybrid) rootstock and were trellised and trained to a 3.0 m tall vertical axis, with a central leader. All trees had reached full maturity at the start of the experiment.

2.2. Mechanical Harvester

This experiment utilized an over-the-row Oxbo-Korvan 930 harvester (Oxbo International Co., Lynden, WA, USA;) modified only by increasing the tunnel height from 2.1 m to 3.7 m (Kathryn Vanweerdhuizen, personal communication, December 2022). This harvester was designed to harvest Jatropha (Jatropha curcas) and was purchased in 2016 (cost USD 71,000) and modified by a grower (Supplemental information). The modified Oxbo-Korvan 930 includes heavy duty Dynarotor head and rods (48 cm length), which rotate at variable speeds that is based on contact resistance. A diesel tractor was used to pull the harvester (Figure 1), with the PTO operating at 540 rpm and the tractor moving in the lowest gear moving at 0.31–0.35 m·s⁻¹.

2.3. Experimental Procedures

Each year cultivars that had high crop load and similar harvest dates were selected for the study. Due to the biennial bearing habit of cider apple cultivars, not all cultivars had sufficient fruit for harvest every year. The study included 10 cultivars in 2021, 12 cultivars in 2022, and 16 cultivars in 2023 (

Table 1. Sixteen cider apple cultivars mechanically harvested using the over-the-row modified Oxbo-Korvan 930 (Oxbo International Co., Lynden, WA, USA) at Washington State University Northwestern Washington Research and Extension Center, Mount Vernon, WA, USA, in 2021–2023.

Cultivars Harvested	Historical Harvest Date 1
2021 and 2023
Ashmead’s Kernel	30 September
Chisel Jersey	29 September
Foxwhelp	4 October
Jouveaux	25 September
Liberty 2	- 3
Porter’s Perfection	26 September
Redfield	-
Roxbury Russet 2	21 September
Russet King	26 September
Smith’s Cider 2	1 October
2022 and 2023
Amere de Berthcourt	25 September
American Forestier	18 October
Brown Thorn	8 October
Brown’s Apple	-
Liberty 2	-
Roxbury Russet 2	21 September
Smith’s Cider 2	1 October
Sweet Alford	7 October
Sweet Coppin	10 October

¹ Harvest dates were recorded 2002 to 2017 in Mount Vernon, WA, USA, and the 15-year average was calculated [16]. ² Indicates that a cultivar was harvested in all 3 years of this study. ³ “-” indicates no historical data for this cultivar at this site.

). All cultivars were harvested at least 2 years and three cultivars were harvested all 3 years. In 2021, only data for mechanical harvest efficiency were collected. In 2022 and 2023, data for mechanical harvest efficiency, tree damage, time required to harvest and fruit and juice quality were collected.

The orchard was sprayed with three commercial plant growth regulator (PGR) products (ReTain, Valent Biosciences, Libertyville, IL, USA; Refine, Fine Americas Inc., Walnut Creek, CA, USA; Ethephon 2SL, ADAMA, Raleigh, NC, USA) at label rates prior to harvest all 3 years. Products were applied to retain fruit on the trees (ReTain and Refine) and then to release fruit (Ethephon) to maximize fruit capture by the harvester. In 2022 and 2023, fruit maturity was measured using the Cornell Starch Iodine Index (CSII; scale 1–8) [17] for five randomly selected apples per plot. In 2022, fruit did not reach full maturity by the end of the season due to inclement weather and were harvested at ~4–6 CSII. In 2023, fruit were harvested within 2 d of half the plots reaching 7–8 on the CSII scale.

Fallen apples were removed from the orchard floor and discarded 14 d and 2 d before harvest all 3 years. Each year, all plots were harvested on the same day. Prior to mechanical harvest in 2022 and 2023, the northern-most tree in each study plot was harvested by hand and the amount of time to hand harvest was recorded. The same day as mechanical harvest, apples that fell to the ground in each plot during harvest and all fruit remaining on the trees after harvest were collected, counted, and weighed separately, then discarded. The number of limbs larger than 1 cm diameter that were partially or completely broken off the tree by the harvester were counted per plot in 2022 and 2023.

All 3 years, mechanically harvested apples were stored at ambient temperature and yield was measured within 3 d of harvest. The number of lacerated fruit were counted per plot in 2022, and for a random sample of 30 fruit per plot in 2023. The total number of fruiting spurs present with the fruit were counted in 2022 and 2023, and mean number of spurs per plot was calculated. In 2023, 30 representative fruit were randomly selected (or all fruit per plot if fewer than 30), weighed, and the diameter was measured. The mean weight and diameter per fruit were calculated for each plot.

In 2022, as all cultivars were harvested before full maturity, fruit were placed in cold storage (4.4 °C) and five fruit per plot were tested each week for maturity using the CSII test. Once the fruit in a plot reached maturity (7–8 on the CSII), fruit were milled (MultiMax 30; Zambelli Enotech, Camisano Vicentino, Italy), pressed (Carezza; Enotecnica Pillan, Camisano Vicentino, Italy), and a 500 mL subsample of juice was frozen (−15 °C) for analysis. All plots reached maturity within 21–35 d post-harvest. In 2023, 25 fruit were milled and pressed within 3 d of harvest, and a 500 mL juice subsample was frozen for analysis. Remaining fruit were placed in cold storage to assess if juice quality declined due to post-harvest storage. At 15 d post-harvest, 25 fruit were milled, pressed, and a subsample was frozen for analysis. For the 12 plots where yield was >20 kg, 25 cold-stored fruit were milled and pressed 32 d post-harvest, and juice subsamples were frozen for analysis. At both 15 and 32 d post-harvest, the number of rotten fruit was recorded for each plot and then discarded.

Each year, all frozen juice samples were thawed and juice quality was measured: total soluble solids (TSS), pH, titratable acidity (TA), specific gravity (SG), and percent tannin (a subgrouping of polyphenols relevant to cidermakers). Juice analysis followed the same procedures as outlined in Kendall et al. [18], summarized here. Juice samples were thawed at room temperature (23 °C) then hand shaken for homogenization. TSS (recorded as °Brix) were measured for two to three drops of juice per sample with a digital refractometer (Palm Abbe model #PA201; MISCO, Cleveland, OH, USA), making sure no bubbles were present and adjusted to room temperature for 30 s. pH was measured for each sample using a digital pH meter (Ohaus Starter 5000; Ohaus Corporation, Parsippany, NJ, USA) by submersing the probe in 5 mL of juice. TA (percent malic acid) was measured for each sample using titration with an auto-titrator (HI932; Hanna Instruments, Woonsocket, RI, USA) with 0.1 N sodium hydroxide (NaOH; Aldon Corp., Avon, NY, USA) to an endpoint of 8.2. TA was calculated as grams of malic acid per 100 mL, using the conversion factor mL NaOH × 0.536 (a constant based on sample volume and normality). SG was measured using a precision hydrometer (SG range 1.000–1.070; Bellwether; VeeGee Scientific, Kirkland, WA, USA) suspended in 200–250 mL of juice. Percent tannin (expressed as tannic acid equivalents) was measured using the Löwenthal Permanganate Titration method [19,20,21]. A blank control was calculated for each batch of potassium permanganate solution (Ward’s Science, Rochester, NY, USA) by titrating the solution into an indigo carmine indicator without juice. The volume of titrant required to turn the indicator solution yellow was recorded as the “Q” value for that batch. For each plot, the potassium permanganate was titrated into 1 mL juice samples mixed with 5 mL of indicator solution until the reference color (yellow) was reached; the volume of titrant was recorded as the “P” value. Percent tannin was calculated by (P − Q)/10.

2.4. Statistical Analysis

Data were analyzed using analysis of variance (ANOVA) in R (version 4.2.2., R Studio, Boston, MA, USA). The relationships between fruit damage and weight, as well as fruit damage and diameter, were analyzed using polynomial regressions with the “nlme” package. The relationships between total fruit and fruit dropped, as well as total fruit and fruit captured, were analyzed using simple linear regressions with the “nlme” package. Juice analysis data were analyzed using paired t-tests (2022) and repeated measures ANOVA (2023) in R. Significance of all interactions was reported at α = 0.05.

3. Results

There were no differences among years (p = 0.88) or cultivars (p = 0.43) for the percent of apples captured by the modified Oxbo-Korvan 930 harvester for the 3 years of this study. Overall, across years and cultivars, 82% of fruit were captured by the harvester and the range was 70–95% (Figure 2). There was no correlation between total weight of mechanically harvested fruit and the percent of fruit that were captured (p = 0.25). There was a positive correlation between total weight of harvested fruit and the percent of fruit that were dropped on the ground during harvest (9% of fruit on average across years and cultivars) (p < 0.001, R = 0.49), but there was no difference among cultivars for percent of fruit dropped on the ground during harvest across years (p = 0.57). There also was no difference among cultivars for the percentage of fruit left on the tree by the harvester across years and cultivars (9% of fruit on average) (p = 0.91). The overall average time required to mechanically harvest one tree in this orchard (1.8 m in-row spacing, 1495 trees·ha⁻¹) was 5.3 s, averaging 2.9 s per row-meter traveled (

Table 2. Amount of time to mechanically harvest cider apples using the over-the-row modified Oxbo-Korvan 930 harvester (Oxbo International Co., Lynden, WA, USA), and to hand harvest one tree per plot for comparison, in Mount Vernon, WA, USA.

Year	Time (s) per Row Meter Traveled	Time (s) to Mechanically Harvest One Tree 1	Time (min) to Hand Harvest One Tree 2
2022	3.1	5.7	4.46
2023	2.7	4.9	3.4

¹ A diesel tractor in low 1 gear moving 0.31–0.36 m·s⁻¹ was used to pull the harvester, which was operated by the tractor’s 540 rpm PTO. ² In-row spacing was 1.8 m.

). The average time required to hand harvest one tree in this study was 229 s (3.8 min) (Table 2).

Overall, 8.0 spurs were removed with fruit per tree during mechanical harvest, and there was a difference among cultivars (p = 0.03). Only one cultivar, Sweet Alford, had high spur removal the two years it was harvested (28.7 spurs removed per tree on average) (Figure 3). When this cultivar outlier was removed from the dataset, there were no significant differences among the remaining 15 cultivars (p = 0.47), and the overall mean spur removal with fruit was 6.2 per tree. A positive correlation was found between total weight of harvested fruit and total spurs removed per plot (p < 0.001, R = 0.52). The overall average number of branches broken during mechanical harvest was 1.4 per tree, and there were no differences among cultivars (p = 0.12) (Figure 4), but there was a difference due to year: 0.9 branches were broken per tree in 2022 and 1.8 in 2023 (p = 0.006).

All of the cider apples captured by the harvester were bruised. There was a positive correlation between mean fruit weight and the percent of apples that had lacerations (p < 0.001, R = 0.53) (Figure 5). Additionally, there was a positive correlation between mean fruit diameter and the percent of apples that had lacerations (p = 0.001, R = 0.39). Juice quality characteristics (

Table 3. Juice total soluble solids (TSS, measured as ºBrix), specific gravity (SG), pH, titratable acidity (TA), and tannin (%) for cider apples mechanically harvested (modified Oxbo-Korvan 930, Oxbo International Co., Lynden, WA, USA) in 2022 and 2023 in Mount Vernon, WA, USA.

		TSS (°Brix) 1		SG 4		pH 5		TA 6		Tannin (%) 7
Year	Cultivar	First Press 2	Final Press 3	First Press	Final Press	First Press	Final Press	First Press	Final Press	First Press	Final Press
2022	Amere de Berthcourt	10.7	13.1	1.042	1.052	4.02	4.06	4.15	4.19	0.27	0.2
	American Forestier	9.5	11.7	1.038	1.047	4.22	4.16	4.1	4.06	0.23	0.1
	Brown Thorn	10.5	11.4	1.043	1.044	4.3	4.45	4.59	4.39	0.22	0.06
	Brown’s Apple	10.8	12.7	1.045	1.05	3.75	3.37	3.98	3.95	0.21	0.07
	Liberty	11.1	12.7	1.046	1.05	3.26	3.55	4.37	4.36	0.19	0.02
	Roxbury Russet	15.9	19	1.069	1.072	3.61	3.65	4.4	4.47	0.2	0.04
	Smith’s Cider	10.4	11.2	1.041	1.047	3.49	3.51	4.43	4.35	0.21	0.04
	Sweet Alford	10.1	12.2	1.045	1.049	4.44	4.5	4.17	3.99	0.17	0.02
	Sweet Coppin	11.1	12.6	1.044	1.055	4.16	4.29	4.07	4.1	0.19	0.04
	p value 8	0.02		0.05		0.60		0.13		<0.001
2023	Amere de Berthcourt	14.7	16.5	NA 8	1.064	3.58	3.87	4.07	3.97	NA 9	NA
	American Forestier	13.9	17.4	1.068	1.074	3.85	4.05	3.91	3.9	NA	NA
	Ashmead’s Kernel	12.3	14.7	1.051	1.059	3.31	3.34	4.13	4.33	0.08	0.1
	Chisel Jersey	9.2	11.7	1.038	1.045	4.29	4.32	3.82	4.04	0.21	0.28
	Foxwhelp	13.5	15.1	1.055	1.059	3.23	3.25	4.15	4.32	0.17	0.21
	Jouveaux	11.8	13.6	1.047	1.052	3.95	4.06	3.88	4.13	0.16	0.18
	Liberty	11.3	12.5	1.044	1.05	3.04	3.48	4.06	4.3	0.06	0.06
	Porter’s Perfection	8.7	10.3	1.035	1.041	3.32	3.46	4.16	4.3	0.22	0.25
	Redfield	11.2	12.4	1.043	1.05	3.19	3.41	4.05	4.38	0.26	0.26
	Roxbury Russet	14.1	15.8	1.058	1.063	3.57	3.63	4.01	4.32	0.06	0.07
	Russet King	13.6	15.1	1.054	1.058	3.41	3.48	4.04	4.38	0.08	0.09
	Smith’s Cider	10.8	12.7	1.045	1.049	3.43	3.39	4.07	4.19	0.07	0.07
	Sweet Alford	12.2	13.5	1.049	1.056	4.64	4.48	3.75	4.03	0.07	0.08
	Sweet Coppin	14.6	17.9	1.063	1.073	3.77	4.17	3.98	3.92	NA	NA
	p value	0.008		0.03		0.25		<0.001		0.42

¹ Total soluble solids was measured using a digital refractometer (Palm Abbe model #PA201; MISCO, Cleveland, OH, USA). ² The first press occurred within 3 d of harvest. ³ The final press occurred after 15–35 d in cold storage, when fruit reached 7–8 on the Cornell Starch Iodine Index. ⁴ Specific gravity was measured using a precision hydrometer (Bellwether; VeeGee Scientific, Kirkland, WA, USA) suspended in ~200 mL of juice. ⁵ pH was measured using a digital pH meter (Ohaus Starter 5000; Ohaus Corporation, Parsippany, NJ, USA). ⁶ Titratable acidity was measured using an auto-titrator (HI932; Hanna Instruments, Woonsocket, RI, USA). ⁷ Tannin (expressed as tannic acid equivalents) was measured using the Löwenthal permanganate titration method [20,21]. ⁸ p-values were calculated for first to final press, for all cultivars combined. ⁹ NA = data not available due to low juice volume.

) differed between years as fruit were not fully mature at harvest in 2022 but were fully mature at harvest in 2023. In 2022, fruit matured while in cold storage and reached full maturity by 21–35 d after harvest. TSS increased 16% on average with cold storage in 2022 and 2023 (p = 0.02 and 0.008, respectively), while SG increased 8% only in 2023 (p = 0.03) but not it 2022 (p = 0.05). There were no differences in pH either year after fruit were cold-stored (p = 0.60 and 0.25, respectively). TA did not differ due to cold storage in 2022 (p = 0.13) but increased in 2023 (p < 0.001). There were differences in percent tannin due to cold storage in 2022 (p < 0.001) but not in 2023 (p = 0.42). In 2023, the greatest amount of fruit with rot was ~4% after 15 d in cold storage, and was ~6% after 32 d.

4. Discussion

The harvest efficiency of the modified Oxbo-Korvan 930 was ~82% (range was 70–95%) for the 16 cultivars in this study. Most of the apples that were dropped by the harvester (~9% of total yield) bounced out the front of the harvester or were shaken off before the harvester was positioned over the tree, due to the harvester shaking the trellis wires. Softening the surface of the catch plates, as has been done for mechanical harvesters for blueberries [22], would reduce the number of fruit bouncing out of the harvester. Extending the catch plates further in front of the harvester to catch apples and then funnel them back to the conveyer belts would also increase the machine’s capture efficiency. The time to harvest one tree with the modified Oxbo-Korvan 930 was more than 40-fold less than by hand. Not including the time to turn around and offload/reload harvest crates, three individuals could harvest 10 ha of cider apples in less than 22.5 h with the modified Oxbo-Korvan 930 harvester.

Larger cider apples, by weight and diameter, had more lacerations due to mechanical harvest compared to smaller apples. Lacerations serve as entry points for bacteria and fungi to cause decay and rot, and thus, larger cider apples may not store as well as smaller apples after mechanical harvest. Yet after 15 d in cold storage, the greatest amount of fruit removed due to rot was ~4%, and was only ~6% after 32 d. Typically, if cider apples are harvested at maturity, they are pressed within a few days or weeks. Thus, yield loss due to fruit damaged due to mechanical harvest and developing rot would be minimal. Further, fermentation serves as a kill-step for unwanted microorganisms present in the decay of damaged fruit [12].

Spur removal during mechanical harvest was minimal. However, longer term studies are needed to determine if cultivars with high spur abscission are suitable for over-the-row mechanical harvest. The number of branches broken by the harvester was also minimal, and was consistent among cultivars and years. Branch breakage could be minimized by training new branches to be horizontal. We observed that branches that grew at steep angles, rather than horizontally, were more likely to break as they had less flexibility to move through the rotating, horizontal spindles of the harvester. It may be important to apply appropriate pesticides after harvest to reduce the introduction of disease through damaged wood.

The juice quality of mechanically harvested cider apples was minimally affected due to storage time except that sugars increased across all cultivars, as expected. While tannin concentration decreased as fruit reached full maturity [23,24], a fully mature cider apple with higher levels of sugars is more desirable for the fermentation process in cidermaking. Acidity, measured through pH and titratable acidity, was largely unaffected by time in cold storage in this study. This may have been due to the specific cultivars examined or the minimal time fruit were in storage (<35 d), as others have reported that acidity in apples tends to decrease with time in cold storage [25,26,27].

5. Conclusions

Mechanical harvest using the modified Oxbo-Korvan 930 required 40-fold less time than hand harvest, which is significantly more labor-efficient. The picking efficiency of the modified Oxbo-Korvan 930 harvester could be increased from 82% to >90% with relatively simple harvester improvements, such as softening the catch plates surface and extending the catch plates in front of the harvester. All of the fruit that was shaken from the trees but not captured by the harvester either bounced out of the front of the harvester or were shaken off the tree ahead of the catch plates. Softening catch plates and other hard surfaces inside the harvester to reduce fruit bouncing and bruising has been implemented for blueberry mechanical harvesters that are similar to the harvester technology used in our study. Loss due to rot of mechanically harvested fruit during 32 d post-harvest cold storage was minimal (4–6%) and juice quality did not decline. These results demonstrate that the modified Oxbo-Korvan 930 harvester is suitable for cider apples.

Optimizing the orchard system for over-the-row harvest includes using rootstocks to produce tree height of approximately 3.0 m, pruning to a fruiting wall, and avoiding trellising systems if possible. Trellis systems add significant cost to orchard establishment and the wires are shaken by the harvester, leading to fruit loss during harvest. Cultivars that are best suited for mechanical harvest should not have pre-mature fruit drop, so they are suitable for a one-time harvest. Small-sized fruit could be especially well suited to mechanical harvest. First, they had less damage from mechanical harvest than larger fruit. Second, the amount of time to hand harvest small fruit can be up to four times greater than for larger fruit [8].

More research is needed to assess yield and tree health following multiple years of mechanical harvest. Testing is also needed to evaluate viability of over-the-row harvest in a commercial cider apple orchard setting. There is a need to assess costs and returns of medium- and high-density fruiting wall orchard systems combined with over-the-row harvest, and compare with traditional cider apple orchards with standard-size trees and current harvest techniques.