Bruising and Its Control in Apples

Definition of Bruising

Bruising is an injury to the apple and is a function of the shock loading on the apple—either static (pressure) or the forward or downward speed (velocity) when the apple comes in contact with another fruit or surface, causing it to expend its kinetic energy.

Bruising is a function of many variables:

1. Some years are more bruise-prone than others.
2. The more mature the apple, the more bruise-prone it becomes (softer apples suffer larger bruises from the same shock).
3. Soil moisture can influence severity. Apples picked after rain or with soil moisture at full capacity bruise more easily than those picked as soil moisture declines.
4. Apples picked in the early morning bruise more easily than those picked after warming up during the day.

Where and When Do Apples Bruise?

Apples can be damaged throughout the handling chain, from the tree to the consumer, causing loss of product value.

• (P) denotes pressure bruising.
• (V) denotes velocity bruising.

At Harvest or Picking Time

1. Picker holds two or more apples in hand. (P)
2. Picker drops fruit through the tree, hitting another apple on the way down. (V)
3. Picker drops fruit into picking bag or basket. (V)
4. Picker overfills the picking bag. (P)
5. Picker lengthens the string of the picking bag for more volume and less walking; fruit bumps against knees when walking. (V)
6. Picker bumps bag against ladder (V) or squeezes bag between body and ladder (P)
7. Picker empties bag roughly into the bin. (V)
8. Bin sorter bruises fruit through rough handling when looking for defective fruit in the bin. (V)
9. Caution: When changing from one variety to another, pickers may handle Golden Delicious as roughly as Packham’s Triumph or red apples, causing damage. (V)
10. A tired picker will bruise fruit more often and severely than one who is rested and fit.

Transport to the Packing Shed

1. Defective bins cause bruising. (P)
2. Badly graded roads or holes or bumps in orchard cause bruising (P & V), especially if picking trailers are not sprung.
3. Tractor drivers who drive too fast can cause severe damage over bumps. Damage can also occur with bin sway, especially to the last bin on the last trailer. (V)
4. With the bin-on-the-ground system, overfilled bins can cause severe bruising when a second bin is placed on top. The centre bearer presses down on the top fruit, causing bruising through the bin.

The Forklift

1. Forklift operator can cause severe bruising if the bin is lowered too fast and comes to a halt with a bump. (V)
2. By bumping the bin from the side or misdirecting the fork. (V)
3. Defective bins can cause severe bruising, especially if the bottom of the bin moves relative to the sides when lifted or put down. Bins with halved centre bearers and firmly connected bottom side planks are preferable.
4. A bin that bulges sideways (e.g., plywood bins) can cause severe bruising, especially when hit from the side by a forklift. (P & V)

Down the Packing Line

1. Dry dumping at too great a speed. (V)
2. Invert dumping in water when opening the lid too early, i.e., above the water before the inverted bin is lowered into the water. (V)
3. All drops down the line must be well padded. Padding should deaden the impact rather than make the fruit bounce and hit the next fruit. Curtains are essential to slow down forward movement. (V)
4. Fruit must drop free from rollers onto the drop board; otherwise, fruit can be pinched between the drop board and roller. Place the drop board just below the centre line of the shaft driving the roller. (V)
5. Sorters can bruise fruit through rough handling and by throwing fruit onto the belt above. (V)
6. The sizing machine should be well curtained and padded to prevent apples bumping against each other as they are dropped onto the belt, especially when the sizer is moving fast. (V)
7. Overfilled packing tables can cause severe bruising (P & V). Ensure tables only have a single layer of fruit, especially with Granny Smith and Golden Delicious.
8. The bin filler operator can cause severe bruising with incorrect control and feed into the bin, both wet and dry. Watch for overfilled bins. (V)
9. A rough packer who packs too fast can cause severe damage by misplacing apples or hitting another apple in the box. Monitor all packers regularly. (V)
10. Some pulp trays can be more rigid than others, especially if the moisture content is incorrect. Pulp trays in cold stores without plastic wrap will absorb moisture and soften. (P)
11. Incorrectly set strapping machines can cause bruising throughout the carton, especially the top layer. (P)
12. A jiffy pad instead of an inverted pulp tray on the top layer gives more protection. (P)
13. Uneven sizing causes uneven loading on larger apples and severe bruising. (P)
14. Apple trays placed incorrectly in the carton (back to front) cause uneven loading and bruising. (P)
15. Pallet stackers can cause shock loading and bruising within the carton by throwing cartons onto the stack. (V)
16. Pallet stacking in the cold store without pallet support can cause uneven loading and collapse of cartons, causing pressure bruising. (P)
17. Forklift drivers must be trained to handle palletised loads correctly; otherwise, sideways or top-to-bottom bruising will occur. (V)
18. Bagging of apples can cause severe bruising, especially if done automatically by machine. Even place pack thrift bags can cause more bruising than carton packs if handled incorrectly. (V)
19. Walking on top of cartons in recooling tunnels or when pulling the sail over the load on the transport vehicle is not recommended.

Prevention and Control of Bruising

1. Implement a good quality control or monitoring system from picking through transport and the pack-house to prevent or halt damage if bruising appears.
2. Know your fruit, its stage of maturity, and whether it is more bruise-prone.
3. Ensure the quality controller is properly trained and knows what to look for.
4. Sample fruit from various places in the picking line at least twice weekly, leave for 24 hours, and then examine for bruising.
5. A better method: stop the packing line full of fruit at closing time and examine the fruit the next morning, two hours before packing commences. Increases in bruising will show up clearly.
6. Work in conjunction with your inspector as a team; they can assist greatly in preventing damage before it goes too far.
7. Do not allow anyone to walk on top of pallet stacks, whether in the cold store or on the transport vehicle.
8. Use pallet support systems when stacking more than one high in the cold store.
9. As taste and flavour become more important, bruising will occur more easily as apples soften and become more tree-ripened; handle more gently.
10. Electronic apples are available worldwide to help select the best machine to handle fruit or pinpoint where damage is occurring on existing machinery.

Wilting to Reduce Bruising

Wilting or removing excess moisture from the fruit makes apples less turgid, using air management and lower relative humidity in cold stores at -0.5°C.

1. Do not attempt to wilt at ambient temperature as this can cause severe stress and man-made bitter pit.
2. When removing excess moisture in the cold store, ensure air passes over and through the fruit in bins, not around the bins. Air must be forced through the bins using mobile fans, curtains, or by filling the back wall of the cold store.
3. To wilt in a cold store, lower relative humidity to 70–75%. This requires large temperature differences (T.D.) between the coolant and the air passing through coils.
4. Modern cold stores are designed for high relative humidity (90–95%). Only during pull-down is there a large T.D. Once fruit is at temperature, the T.D. drops and humidity rises, so little moisture is removed.
5. Two methods to lower relative humidity in modern RA cold stores:
   • On/off method: Override the back-pressure regulator with the low-temperature thermostat, maintaining a large T.D. while the regulator is open.
   • Reduce cooler surface area: Close valves to one or two cooler blocks and block airflow through these coils.
6. Immature fruit wilts more than mature fruit. Golden Delicious picked early needs low humidity for one week before packing; mid-window fruit needs 10 days; late-window fruit needs 14 days, always with air moving through the fruit.
7. Apples wilted for too short a period lose moisture only under the skin, which is reabsorbed in water and bruises as easily as if never wilted. Moisture loss should occur throughout the fruit.

Do’s and Don’ts in Precooling and Recooling in Cold Stores

1. Air management is as important as temperature management:
   • ±0.4 m³/sec of air per pallet of fruit is required.
   • Air must pass through cartons on the pallet, not bypass through gaps.
   • Pressure drop across the pallet stack should not be less than ±10 mm of water gauge.
   • Forward velocity of air in the plenum should not exceed 5 m/sec.
   • Cooling pallets stacked 3 high is difficult; gaps are hard to seal and labour is less productive in these conditions.
2. Temperature management: Maintain temperatures to avoid freezing damage. Temperature off the coils should not rise above 0°C. Monitor return air temperature to assess cooling effectiveness.
3. Place 1 or 2 thermocouples in each pallet to determine cooling potential.
4. Insert the thermocouple into the flesh of an apple in the middle carton, third or fourth layer.
5. Occasionally place a thermocouple in an apple on the outside of the pallet stack to monitor cooling and prevent freezing damage.

Source: JS Findlay, 1992. G/RICHARD/TECHNOLOGYTRANSFER/BRUISING – JFINDLAY1992