How to Reduce Internal Bruising Damage of Fresh Blueberries During Mechanical Harvesting

By Wei Yang
Professor and Blueberry Extension Agent

Machine harvesting systems have been available for harvesting processed blueberries for over 30 years. However, they have caused internal bruising damage (IBD) to harvested fruits. Excessive fruit IBD is unacceptable for fresh market berries due to poor quality and a short shelf life. To reduce fruit IBD during mechanical harvesting, several factors need to be considered. The first step is to select cultivars that are less prone to bruising during machine harvesting and have slow IBD development during cold storage. In field studies conducted over the past few years, cultivars such as ‘Duke,’ ‘Draper,’ ‘Aurora,’ ‘Last Call’ and ‘Legacy’ have shown slow IBD development during cold storage. Therefore, these cultivars are ideal choices for machine harvesting for fresh market operations.

Wei Yang, Professor and Blueberry Extension Agent

Blueberry cultivars vary in plant size, and the detached berries can fall as much as 50 inches, depending on their position on the bush during machine harvest. When an over-the-row (OTR) harvester picks blueberries and fruit falls on catch plates and conveyor belts, fruit IBD develops due to the impact force. The higher the fruit falls, the greater the damage. Reducing the fruit drop height can be achieved by pruning off unwanted fruiting wood, thus lowering the bearing surface. Planting on raised beds can maintain proper drop height to increase machine harvesting efficiency. It is important to minimize bruising during the transfer of the fruit to the collection flats. Improper fruit handling during harvesting, such as dropping or bouncing the berries, can also lead to bruising.

Harvest timing is another important factor to consider for reducing IBD. Overripe berries are more susceptible to bruising during machine harvesting because they are softer and less able to withstand the mechanical forces applied. Depending on the cultivar and crop load, mechanical harvesting for the fresh market can begin at 40-70 percent blue stage. The timing to start and stop machine harvest during the day can significantly affect fruit IBD. When the field temperature is over 75°F in late morning or early afternoon, the berries become soft and stick more to the harvesting equipment, causing bruising damage to the fruit during the mechanical picking process. The fruit may also be trapped between the catching surface, causing it to be squeezed, leading to bruising. While it is inevitable to remove overripe berries along with blue and green fruits during machine picking, an experienced harvester operator can adjust the harvester settings to maximize the removal of ripe fruits and minimize the removal of green and red berries.

Adjusting the ground speed, beater frequency and amplitude of the harvester based on the fruit’s ripeness can result in higher quality fruit and reduced fruit IBD. In general, the longer the duration of impact to detach the ripe fruit, the greater the likelihood of IBD development. For example, in ‘Draper’ during machine harvesting, at a fixed ground speed of 0.5 miles/hour, increasing the beater frequency and amplitude resulted in 50 percent more IBD, 200 percent more stems and 10 percent fewer blue fruits harvested. At a fixed frequency and amplitude, the longer the duration of agitation due to a slower ground speed, the greater the impact, which increases the potential for IBD development. An increase in the harvester’s ground speed from 0.3 miles/hour to 0.75 miles/hour during ‘Draper’ harvesting resulted in decreased fruit firmness and a lower percentage of blue fruit harvested.

The recent development and commercial availability of a soft catch system in the OTR harvester can help to reduce blueberry fruit bruising during machine harvesting. By using a soft catch surface, the impact on the blueberries is reduced and the likelihood of bruising is minimized. Soft catch surfaces can also help to evenly distribute the weight of the blueberries, further reducing the potential for impact damage. Studies conducted by OSU over the past several years have demonstrated a reduction in IBD of more than 50 percent when using the soft catch kit on an OTR machine harvester while harvesting ‘Legacy.’ In ‘Draper’ harvesting, the use of a soft catch kit on the OTR harvester resulted in a 40 percent reduction in IBD. It is worth noting that the effectiveness of a soft catch surface in reducing blueberry fruit bruising may depend on various factors, including the ripeness of the fruit, the harvester settings and the design of the soft catch surface. Therefore, it is important to evaluate the specific field conditions and requirements of fresh harvest operation to implement the most effective methods for minimizing fruit IBD during machine harvesting.

In addition, fruit handling, transportation and packhouse operations can potentially cause bruising damage to the fruit, which necessitates the removal of any affected fruits during the packing process. However, by carefully selecting postharvest handling temperature and implementing appropriate cold treatments, the development of fruit IBD can be slowed down, resulting in better fruit quality.

Therefore, it is crucial to work closely with a packing house and have a thorough understanding of their processes and requirements to ensure a successful machine harvesting operation for fresh market berries.