In the UK greatest attention has been made in determining the harvest maturity parameters for the storage of Cox apples. Comprehensive studies of the relationship between harvest maturity parameters and the storage quality of Cox apples have been carried out since 1994, under the auspices of the UK Quality Fruit Group (QFG).
The QFG was formed in response to the poor performance of Cox apples on the UK market in 1992 and 1993. The UK national maturity indexing programme began in 1994 with funding provided by English Apples and Pears Ltd. Now that the majority of growers and their marketing groups conduct their own maturity programmes in the lead up to harvest, the QFG has been discontinued but its presence helped the industry to improve the way in which maturity testing is conducted.
Picking dates of Cox for storage should be guided mainly by firmness of the fruit at the point of harvest using the threshold levels given in Table 7.
Table 7. Relationship between harvest and ex-store firmness (penetrometer fitted with an 11 mm probe) for Cox apples. Fruit stored under recommended conditions of 1.2% O2 (<1% CO2) at 3.5oC (see Section 9)
|Ex-store firmness||Harvest firmness (kg)|
* Storage of Cox in 1.2% O2 (<1% CO2) should be completed by the end of March
Recognising the need to achieve acceptable levels of sensory attributes in addition to texture, the harvest firmness levels associated with 6 kg firmness ex-store were adopted by the QFG. Picking for adequate ex-store firmness almost always ensures adequate ex-store greenness of the background colour and provided that fruit mineral composition complies with recommended standards then physiological disorders related to senescence should be avoided.
Changes in starch pattern should also be taken into account, as, in some years, the change in firmness is too gradual to provide a clear indication of when to pick.
Ideally 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%.
Provided that starch levels comply with the recommendation then firmness can be used as the deciding factor on when to harvest. However, where firmness remains high but starch degradation reaches 90-80% then picking for mid- to long-term should commence and be completed by the time that starch declines to 70%.
At the present time the use of firmness and starch pattern are considered more informative than the ‘Streif’ maturity index that combines both attributes together with soluble solids concentration.
(However, the ‘Streif’ index is preferred to individual harvest parameters for determining the correct harvest date for Conference pears. Conference pears for long-term storage should be picked before the ‘Streif’ index falls below 0.7.)
In the ‘Bodensee’ region of Germany a ‘Streif’ index of 0.21 (equivalent to 2.1 when using the formula presented above) was associated with the optimum harvest date for Cox apples. However, the evaluation of quality ex-store was on the basis of sensory tests, objective measures of quality such as firmness, acidity, soluble solids and background colour, and incidence of diseases and disorders.
This assumes that the interests of consumers and growers can be represented in an overall quality score for the product. In reality there is probably zero tolerance by consumers to diseases and disorders and improved scores for some sensory attributes that result from later harvesting do not compensate for other deficiencies in the fruit.