Best post-harvest practices for Cripps Pink apples

Compiled by Store‐it Group for Hortgro Science.

NOTE: these best-practice guidelines are regularly updated. Please consult the Hortgro website for the latest version.

What is the correct harvest maturity for long-term storage?

• Starch breakdown <40%. Optimum is 20%–30%. Can be released at 15% depending on other parameters.
• Firmness >7.8 kg when measured with an 11.1 mm tip.
• Total soluble solids should be >12.5%.
• Titratable acidity 0.75%–0.55%.
• Maturity is the biggest risk factor for development of diffuse browning after storage. Post-optimum harvested fruit should never be stored long-term.

Dealing with variability

• Rank orchard maturity four weeks before harvest and assess pre-delivery samples to determine ripening rate and storability.
• Market fruit from orchards with faster ripening rates first and do not store in CA.
• Determine inside- and outside-canopy fruit maturity. The outside, well-coloured fruit will be harvested first due to block colour standards of 40–60%. The inside pale fruit will be left longer to colour up.
• Inside-canopy fruit may be riper — even at the first pick — and should not be stored in CA for longer than 12 weeks.
• Consider leaf-stripping after first pick when sunburn risk has diminished. Rather consider reflective mulching should sunburn be a risk.
• The second pick may be put into CA for long-term storage depending on the starch breakdown.
• Avoid a long picking window.
• Do not CA-store fruit with starch breakdown >50% for longer than 12 weeks. It may be acceptable for RA and RA + 1-MCP and short-term CA storage.

Orchard history effects on long-term storage

• Do not store fruit from young trees for longer than 12 weeks.
• Light crop-load fruit may be more susceptible to earlier ripening and disorders.
• Under- or over-irrigation may result in faster ripening rates and poor storability.
• Fruit from orchards on sandy soils tend to ripen faster.
• Mineral nutrition is important in ripening rate and storage quality.
• Consider the history of progressive defects and ripening rates of each orchard.
• Topworked trees may have a higher internal browning risk due to increased stress.
• Fruit that received any type of stress during the season should be sold within 6 weeks.

Post-harvest and storage handling

• Harvested bins should not remain in the sun. Accumulate in a shaded area and transport to the packhouse as soon as possible.
• At the packhouse fruit should be loaded into the cold room as quickly as possible. Fruit should not be accumulated outside the packhouse in the shade or overnight to facilitate initial cooling.
• Be aware that cold-room temperature can fluctuate excessively while adding warm fruit. Separate warm and cooled fruit with curtains in the cold room to help avoid this.
• Make sure that the cold room has sufficient cooling capacity for the volume of warm fruit.
• Load two or three rooms simultaneously to get even cooling rates.
• Attain pulp temperature of 4 °C after 48 hours. Fruit should further be cooled stepwise.
• CO₂ levels should be monitored when warm fruit are closed in a cold room.
• CO₂ levels should never reach levels >1%. Use additional lime or new generation scrubbers to reduce CO₂ to 0.5%.
• Fruit will benefit from ethylene inhibitors — 1-MCP — to reduce ripening rate, greasiness, superficial scald, and internal browning. Treat within 7 days of harvest especially if stored for up to 3 months in RA or >3 months in CA.
• Diffuse and radial browning is reduced when using step-down cooling rather than single-storage-temperature regimes of 1°C for long-term — >7 months — storage in CA.

Industry guidelines for CA O₂ and CO₂ gas regimes

ARC/HORTGRO

• Nitrogen flushing: attain gas regime of 3% O₂ + 1.5% CO₂ within 48 hours of sealing the room.
• Optimum O₂ level is 1.5%. Minimum 1%. Maximum 2%.
• Optimum CO₂ level is 0.5%. Minimum 0%. Maximum 1%.

DCA guidelines

DCA- RQ / ACR system (Van Amerongen) | (PACKHOUSE EXPERIENCE / VA)

• Room filling — 5-7 days. Keep CO₂ <1%.
• Room full — 3 days. Fruit on temperature. Keep CO₂ <1%.
• Pull down O₂ to max 6% — 2 days. Keep CO₂ <1%.
• O₂ reduction to 1.2% — 7 days. Keep CO₂ <1%.
• O₂2% — 14 days. CO₂ <1%. Total 28 days.
• ACR mode from 28 days onwards. O₂ >0.6%. CO₂ <1%.
• Keep O₂ between 0.5%–0.7% depending on the season.
• Always keep CO₂ as close to 0.5% as possible.
• It is a good idea to monitor the fruit from DCA for ethanol levels.
• Please contact your service provider for their specific guidelines.

DCA-CF system (Isolcel / Gas at Site) (ARC GUIDELINE)

• Load the room and cool to core temperature within 48 hours of harvest.
• Allow 5 days for loading the room.
• Then seal and pull down to 3% O₂ + 1.5% CO₂ over 2 days.
• For the next 2 days pull down to 1.5% O₂ + 1% CO₂.
• Pull down to lower O₂ limit + <1% CO₂ within the next 2 days.
• Therefore, the total time from harvest to lower O₂ limit is 11 days.
• After spiking, adjust to 0.2% O₂ above spiking and keep CO₂ <1% during storage. Monitor for spiking during storage period.
• Please contact your service provider for their specific guidelines.

Internal browning considerations

• Fruit maturity — starch breakdown — is linked to development of diffuse browning after storage and ripening.

1. 1. Starch breakdown of 15%–40% and storage up to three months: lower risk of diffuse browning.
   2. Starch breakdown of 15%–40% and >3 months’ storage: risk of diffuse browning depends on other factors.
   3. Starch breakdown of 40%-50% and storage up to three months: medium risk of diffuse browning.
   4. Starch breakdown of 40%-50% and >3 months’ storage: higher risk of diffuse browning.
   5. Starch breakdown more than 50%: high risk of diffuse browning within three months storage.

• Low storage temperature is linked to the development of diffuse and radial browning. Storage temperatures of minus 0.5 °C up to 1 °C have previously been linked to diffuse browning after only 3 months of storage.
• The step-down cooling treatment protocols described below performed better during the past season in terms of diffuse and radial browning for long-term CA storage — >7 months — compared to single-storage-temperature regimes at 1°C. Cooling regime number 2 seemed to perform the best in terms of fruit quality. But note that any stepwise cooling is better than none at all.

1. 1. 1-MCP within 7 days + 30 days at 4 °C, 30 days at 3 °C, 30 days at 2 °C, remaining days at 1 °C.
   2. 1-MCP within 7 days + 30 days at 3 °C, 30 days at 2 °C, remaining days at 1 °C.
   3. 1-MCP within 7 days + storage at commercial CA facility: 2 °C for 14 days + 1 °C for 14 days + remainder at 0.5 °C until room opened. Transferred to US-CA-storage from September 2018 and stored onwards at 1.0 °C with 1.5% O₂ and 0.5% CO₂.

• Pre-harvest factors that affect maturity — see above — have been linked to diffuse browning.
• Cripps Pink is CO₂ sensitive and readily shows CO₂ browning in cases where CO₂ increased above 1%.
• Non-perforated bags could lead to the build-up of CO₂, especially with fluctuating temperatures during shipping and distribution.
• Consider having shipping container vents 15% open due to CO₂ sensitivity and risk of temperature fluctuations during the voyage.