Best Practice Guidelines: Prevention of Pitting in Cherries

General Information

• Pitting is caused by mechanical damage to cells in the flesh of the fruit:
  • At harvest
  • During transport between the orchard and packhouse
  • During packing
  • In transit to the market
• Damaged cells lose moisture and collapse, resulting in pits, depressions, or sunken skin on the shoulders, sides, and/or stylar end of the fruit.
• Pitting only becomes visible 7–10 days after the mechanical damage occurs, as moisture takes time to escape from the damaged cells. Therefore, pitting is usually not seen during fruit inspection prior to export or before local market transport. Generally, the client is the first to see the defect.

Types of Mechanical Injury Causing Surface Pitting

• Impact: When fruit are dropped onto a hard surface or another object is dropped onto the fruit.
• Compression: When fruit press against each other or a hard surface.
• Vibration or Abrasion: When fruit rub against each other or another surface.

Key Factors to Prevent or Minimise Pitting in the Handling Chain

• The stem condition and gloss of the fruit deteriorate quickly after harvest due to cherries’ high respiration rate and low levels of stored carbohydrates.
• Mechanical injury increases respiration rate, ethylene production, and moisture loss, causing even faster fruit deterioration.
• The best way to prevent rapid deterioration and minimise pitting is to cool the fruit to a pulp temperature of 10°C as quickly as possible after harvest.
• Cold fruit (<10°C) are very susceptible to pitting injury during the packing process.

Factors to Consider in the Orchard

1. Cultivar

• Know your cultivar’s susceptibility to pitting to implement the best handling protocols.
• Later maturing cultivars are generally less susceptible to pitting due to stronger cell walls that deform rather than rupture.

2. Pre-Harvest Sprays

• Apply three to four calcium sprays from pit hardening to one week before harvest to strengthen cell wall and membrane structure. For optimal rates, consult your local advisor.

3. Crop Load

• Fruit from lower cropping trees are larger, have higher soluble solids and titratable acidity, are firmer, and withstand mechanical damage better than small fruit from overcropped trees.

Factors to Consider at Harvest

1. Harvest Maturity

• Avoid harvesting fruit that are too mature, as they will be too soft to withstand mechanical damage.
• Use skin colour as the main harvest maturity variable; follow the recommended picking window for your cultivar(s).
• Fruit harvested at a dark mahogany skin colour are more susceptible to pitting.
• In warmer areas, consider harvesting at a lighter mahogany colour, as warmer temperatures can inhibit skin colour development.

2. Harvest Protocol

• Harvest during the coolest part of the day; stop harvesting when ambient temperature exceeds 30°C. Fruit harvested later in the day tend to be softer and remain so during storage and marketing.
• Grasp the stems, not the fruit, when harvesting.
• Fruit should never drop more than 15 cm while warm—place fruit gently into picking totes and pour gently into field bins.
• Line field bins with plastic or other material to prevent abrasion and vibration damage during transport.
• Field bin size should minimise compression bruising.
• Keep fruit in the shade to prevent temperature increase and moisture loss.
• Cover field bins with insulated covers, wet foam, or reflective tarps to increase relative humidity, reduce moisture loss, and maintain fruit temperature.

During Transport to the Packhouse

• Transport fruit to the packhouse within 2–4 hours after harvest to remove field heat.
• Keep field bins covered during transport to maintain fruit temperature and high relative humidity.
• If the orchard is far from the packhouse, consider field heat removal in the orchard by hydrocooling. If used, maintain the lowered fruit temperature during transport.

At the Packhouse

• On arrival, pre-cool or hydro-cool fruit to a pulp temperature not lower than 7–10°C. Colder fruit are more sensitive to mechanical injury on the pack line.
• Consider adding 0.2–0.5% CaCl₂ to hydrocooling water to help maintain fruit firmness.
• Place cooled fruit in a holding room at the same temperature until packing.
• Pack fruit within 2 hours after arrival at the packhouse.
• If fruit cannot be packed within 6 hours after harvest, cool to 4°C to manage respiration and deterioration rates. Pack within 24 hours after arrival. If not packed within 24 hours, cool to 0°C. Note: Packing fruit at pulp temperatures below 6°C increases the risk of pitting; take special care to prevent mechanical injury.
• The maximum drop height on the pack line should not exceed 5 cm due to low fruit temperature.
• The highest level of pitting injury in the packhouse is caused by the cluster cutter and hydrocooling prior to box filling:
  • Cluster cutter: Higher throughput reduces fruit-tine impacts. Operate at a speed that prevents clogging (recommended belt speed: 0.4 m/s). Lower tines to belt level or just below to prevent fruit striking the ends.
  • Hydrocooling: In-line hydrocoolers can damage cherries if water falls from excessive height. Water drop height should not exceed 20 cm or should be as close as possible to the top of the fruit. Use a plastic mesh screen to diffuse water and reduce droplet size and velocity, ensuring mesh size does not reduce water flow rate.
• MAP bags or plastic liners can help maintain fruit quality, but good temperature management is essential to prevent internal fruit damage.
• Ideally, cherries should be packed and cooled to 0°C within 4–6 hours after harvest. If not possible, cool to 4°C and pack within 12–24 hours after arrival at the packhouse.
• Store fruit at 0°C and 90–95% relative humidity.
• Prevent temperature fluctuations during cold storage.

Summary: Fruit Temperature Management After Harvest to Reduce Surface Pitting Risk

• If fruit cannot be packed within 6 hours after harvest, cool to 4°C and pack within 24 hours after arrival at the packhouse.
• If fruit cannot be packed within 24 hours after arrival, cool to 0°C.
• Both contingency practices carry a high risk for pitting injury, as cherries at such low pulp temperatures are prone to mechanical damage on the pack line.