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Predicting and choosing optimal harvesting dates for fresh consumption, short and long term storage of commercial apple cultivars and their clones

Correct harvest date

Picking on the correct harvest date is crucial in ensuring that the quality of apples reaching the consumers is optimal and that consignments meet the quality criteria that are set by multiple retailers and the wholesale market.

For each cultivar the time of fruit maturation on the tree varies from orchard to orchard and from season to season. Consequently decisions on harvesting cannot be made based on an arbitrary calendar date.

Growers need to equip themselves with a penetrometer to test the firmness of the fruit and a quantity of a solution containing 1% iodine and 4% potassium iodide in order to perform starch iodine tests.  

Testing for firmness and presence of starch in the weeks prior to the expected harvest date is essential in allowing the grower to draw up a harvesting schedule and make full use of a harvesting ‘window’. This will help to ensure that the fruit from each orchard is at the correct stage of maturity to enable the grower to implement his or her marketing plans.

Growers will need to be aware of information received from the Quality Fruit Group maturity programme and of long-range predictions issued earlier in the growing season. But the final decision on when to harvest must be based on maturity measurements made on fruit from each orchard prior to picking.

It is important that all quality characteristics of the fruit in each orchard are considered in order to achieve maximum profitability. The fruit must be sufficiently large and well coloured to satisfy market demands.

However, the consequences of delayed harvest to achieve higher grade-out of Class 1 fruit must be realised fully and the fruit stored for an appropriate period under suitable storage conditions.  

Picking date criteria

Cox’s Orange Pippin and clones for medium (December/January) to long-term storage (February/March) 

Picking dates of Cox for storage should be guided mainly by firmness of the fruit at the point of harvest. To achieve 6 kg firmness in fruit stored in CA (1.2% O2 <1% CO2) at 3.5oC until January or March, the minimum firmness at harvest should be 8.2 and 8.7 kg respectively.

Growers should not rely entirely on fruit firmness especially in years when the change in firmness is too gradual to provide a clear indication of when to pick. In this situation the change in starch pattern should also be used. Cox for long-term storage should be picked when the percentage of the cut surface stained blue/black is between 80-90% and no lower than 70%.

When starch levels remain high then firmness can be used to decide when to harvest. However, where firmness remains high but starch declines to 90-80% then picking should commence and be completed by the time that starch declines to 70%.

Growers should start testing for starch and firmness about 2-3 weeks before the expected/predicted date for the commencement of harvest for long-term storage.  Experience has shown that mid-August is an appropriate time to begin monitoring Cox maturity in order that a reliable ‘trend’ can be established.

‘Trend’ lines are normally too variable to accurately predict when fruit will achieve critical levels of starch or firmness.  However, approximate predictions can be made using an average figure for starch loss of 2% per day and firmness loss of 0.1 kg per day (‘Effigi’ penetrometer fitted with an 11 mm probe).

·Greatest benefits from SmartFreshTM application are achieved on fruit picked at the correct stage of maturity for storage. However, starch coverage should be less than 70% in order to reduce susceptibility to stem end russet browning.  

Cox’s Orange Pippin and clones for immediate sale or short-term (October/November) storage.

Cox apples with an average starch iodine staining pattern of less than 70% (black) have a higher potential eating quality but are only suitable for short to medium term CA storage (Table 5). They should remain in an acceptable condition for up to 3 months in CA (1.2% O2 <1% CO2) storage at 3.5oC.

·In many cases particular producer or marketing groups have developed their own maturity ‘standards’ in order to supply their retail customers with fruit of a higher sensory quality for a limited period.

Table 5. Harvest maturity parameters issued by the Quality Fruit Group for Cox apples intended for immediate sale and for CA storage for different periods. (N.B. Air storage of Cox apples should be terminated by mid-October unless SmartFreshTM is applied after harvest

 

Marketing periods

Minimum values at harvest

 

Firmness (kg)

(Penetrometer fitted with an 11 mm probe)

Starch

(% cut surface stained black)

Feb/March

8.6

75

Jan/Feb

8.2

70

December

8.0

60

Mid November

7.7

60

Mid October

7.5

50

Immediate

6.5

<50

 

 

Bramley’s Seedling for long-term storage 

·No harvest maturity standards are available for long term stored Bramley.

Earlier harvesting of Bramley is encouraged to avoid fruit becoming too large if left on the tree. However, there is an increased risk of scald and the development of bitter pit will be increased in low-calcium fruit. Late picking increases fruit softening and yellowing and the development of greasiness and flesh breakdown in stored fruit. Bruise susceptibility increases as picking is delayed.

From general experience fruits picked after the middle of September are less likely to provide premium quality after prolonged CA storage.

Greatest benefits of SmartFreshTM application and other strategies to control ethylene production are achieved on fruit picked at the correct stage of maturity for long-term storage.

·Picking Bramley too early and immature for immediate sale can result in consumer dissatisfaction.  English Apples & Pears Ltd. have developed a maturity release index (MRI) for Bramley using firmness, acidity and sugar (soluble solids) measurements of the fruit:

Firmness (kg) x acidity (g/l)                                           =     MRI

            Sugar (%)

 

Growers should not market Bramley with an MRI above 17.

Gala and clones for air and CA storage 

Gala fruit for long-term storage should be picked when the starch coverage has declined to 80-85 (% black)

·Termination dates for storage in air and different CA conditions should be adhered to strictly

Braeburn and clones for air and CA storage 

Growers need to be aware of advice being provided on the best time to harvest Braeburn. This will be available through the Quality Fruit Group (QFG) and other sources.

Maturity criteria for picking for storage are: starch cover of 85-75 (% black) for air storage until December and CA storage until January. Contrary to common practice fruit intended for long-term (March) CA storage should be harvested slightly more mature, starch cover of 80-75%, in order to reduce the risk of superficial scald. Picking at the higher end of these ranges for starch is likely to provide the longest storage potential.

Picking Braeburn at too immature a stage will result in an inferior appearance and eating quality and a heightened susceptibility to superficial scald.

·Picking too late can result in a greasy skin and poor texture of the flesh.

Meridian for CA storage   

·Preliminary advice is to harvest Meridian fruit for storage when the firmness of the fruit is 7.1-7.6 kg.

Discovery  

Discovery has an inherently short shelf-life and needs to be marketed quickly under conditions that slow the rate of softening.

It is particularly important to keep the fruit temperature below 10oC during distribution.