Monitoring the condition of fruit in store

At least once a month assess the eating quality and internal condition of samples of fruit that represent the major orchards within a store. Once a store is opened continue monitoring samples of fruit from all the major orchards regularly and check fruit quality remains above the customer’s specification

Sampling

It is essential to examine stored fruit at regular intervals to check quality and internal condition. Representative samples need to be taken at harvest and placed in a bin under the store hatch.

As fruit from each orchard is loaded into the store one sample should be taken for every proposed month of storage after October.
It is important to ensure that samples are representative of the whole orchard and that there are sufficient samples to provide monthly monitoring of every orchard.
Twenty apples are required per orchard per month. To obtain the samples for monitoring, one apple should be taken from every tenth bin from that orchard as it is being loaded into the store.
If less than 200 bins from an orchard are going into the store then fruit should be taken more frequently e.g. sample every bin from a 20-bin consignment.
The 20 fruits should be placed in a string net and labelled with orchard name, picking date and store number.
This procedure should be repeated for each proposed month of storage after October, by taking apples from the same bins.
The samples should be placed in a bin under the hatch and covered with a layer of fruit.
If a second orchard is to be loaded into the store, fruit from another set of samples should be taken.
Similarly, if fruit from a particular orchard is loaded into several stores then further sets of samples should be taken.

Fruit Assessment

Each month from October a sample of each store/orchard combination should be taken out and assessed.

It should be remembered that the store atmosphere is lethal, and under no circumstances should anybody enter the store.
The safety of the operator must be stressed.
At no time should the operator place any part of his or her body in the store.
People should always work in pairs, and use a ‘boat hook’ or similar extended hook to remove the netted samples.
Store owners and growers should have appropriate Risk Assessments and Standard Operating Procedures in place for sampling fruit from store hatches – these need to be specific for the type of store design present.

Blemishes and disorders

Each apple in the sample should be carefully examined externally for any signs of blemish or storage disorders of the skin. Such disorders include lenticel blotch pit, carbon dioxide injury, superficial scald or damage due to calcium sprays or the use of a post-harvest drenching solution.

Colour

Colour is very difficult to quantify without the aid of sophisticated instruments. The skin of an apple is variable with patches of different shades of green and bleached areas where leaves have shaded fruit. With dessert apples the stripes of red colour within the background colour makes it very difficult to assess.

A subjective method has been adopted in which the 20 fruits are laid out and, using a colour card as a reference (See Table 27 below), the overall background colour described as dark green, green, light green, light yellow or yellow.

The percentage of the surface area of the fruit coloured red is estimated for each fruit and expressed as a range. To ensure consistency the light condition used should be good and the same for each assessment.

Firmness

Ten fruits from the sample should be selected at random for firmness measurements. Average values taken from month to month provide a general indication of the softening rate of stored apples.

The most widely used instrument for measuring firmness is the hand-held ‘Effigi’ penetrometer. For more consistent results this should be mounted in a drill stand and supported on a firm base. An 11 mm diameter probe should be used for apples and an 8 mm probe for pears.

The instrument should be calibrated against an accurate balance at least once a year. Fruit juice is very corrosive and thus the instrument should be washed, dried and coated in a thin mineral oil after use.

The following procedure should be adopted when carrying out the test:

Remove a thin slice of peel from opposite sides of each of 10 apples.
Lower probe into the flesh at a steady rate.
Take 2 seconds to travel 8 mm into the fruit.
Record value and reset.
Repeat on the opposite side of the fruit.

Where this procedure has been adopted little difference has been found in the readings obtained by different operators. However, to guard against any possible ‘operator error’ the same person should carry out the tests whenever possible. It is recommended that individuals using penetrometers should compare their results occasionally to safeguard against any operating errors. Where access to a motorised penetrometer is available (e.g. Fruit Texture Analyser – FTA), this avoids discrepancies in results between operators.

Disorders

The ten apples used for measurement of firmness are then examined internally for the presence of disorders of the flesh.

A transverse cut is made close to the calyx end of the apple and the presence or absence of bitter pit or browning recorded.
A second cut is made across the equator of the fruit through the core area and the cut surface assessed for core flush, low temperature breakdown and senescent breakdown.
In Gala, Braeburn and Envy, it is advisable to undertake an additional cut at the stalk end of the fruit to examine for ‘shoulder breakdown’ in fruit.
The severity of the breakdown is quantified by assessing the area of the cut surface affected. Slight is up to one third, moderate is between one and two thirds and severe above two thirds.
During the examination fruits are tasted and scored for eating quality and the presence of any taints or ‘off-flavours’ should be noted.
The remaining ten apples are placed in a room at 18^oC and the external and internal condition assessed after seven days.

The mean fruit firmness, together with the percentage of fruit with various disorders, should be calculated and recorded on a purpose designed form. By using one form for each store/orchard combination the change in fruit quality or the development of storage disorders with time can be followed clearly.

Monitoring of Storage Conditions

Successful storage is a combination of the right fruit stored under the right conditions. If the temperature or oxygen is too high fruit will mature quicker and, if too low, there is a risk of damaging the flesh or fruit developing alcoholic taints. If the carbon dioxide is too high there is a risk of damaging the fruit, if too low the rate of change in background colour from green to yellow will increase.

It is therefore very important not only to check the fruit condition regularly but also the storage conditions. Computer based systems provide automatic control of storage conditions and are essential where low oxygen levels are being used. However the printed output generated from such systems is often difficult to interpret.

It is important that store operators maintain a manual record of store conditions. At least once a day the temperature, CO₂ and O₂ levels should be entered in a logbook using a separate page for each store.

This provides evidence that the storage conditions for each store have been checked each day and makes it easy to see overall changes in storage conditions during each month. During the monthly inspection of fruit samples the store logbook should be examined.

Fruit Quality Standards

All fruit in store should remain above the minimum quality standards required by the customer and have sufficient quality to allow for a seven day shelf life. WFL-Qualytech minimum standards are given in Table 27, but you should consult with your own marketing desk at the beginning of the season to ensure that information available is the most up to date.

Table 27. WFL-Qualytech minimum fruit quality standards. Firmness is defined in terms of an average for 10 apples and the minimum recorded for any of the individual apples within a 10-fruit sample

Cultivar	Background Colour Card 1, green – 4, yellow	Firmness (kg) Electronic Penetrometer	Soluble Solids (%) Refractometer
Cox	Green – Light Green (1-2)	Mean 6.5 Min. 5.8	>12
Gala	Light Green – Light Yellow (2-3)	Mean 6.2 Min 5.8	>11.5
Jonagold	Green – Light Green (1-2)	Mean 6.0 Min. 5.5	>12
Braeburn	Light green – Light Yellow (2-3)	Mean 7.2 Min 6.7	>11.5
Bramley	Green – Light Green (1-2)	Mean 6.5 Min. 5.5	>12

During the establishment of storage conditions Cox fruits may lose 0.5 to 1.0 kg in firmness. Subsequently the rate of softening in store depends on the oxygen level, the lower the level below 3% the slower the rate. Generally the following rates of softening have been found for Cox stored at 3.5^oC:

5%CO₂ + 3%O₂: 0.3 – 0.4 kg per month.

<1%CO₂ + 2%O₂: 0.2 – 0.3 kg per month.

<1%CO₂ + 1.2%O₂: 0.1 – 0.2 kg per month.

Post-storage management

All CA stores should be opened before the fruit quality falls below the recommended standards and has sufficient reserve quality to ensure all product reaches the consumer in prime condition

Provided there is not a seasonal high risk of low temperature breakdown, the temperature of fruit in Cox stores should be lowered to 1^oC once opened. The rate that fruit softens is significantly reduced as the temperature is lowered.

Historically fruit store monitoring has been confined to netted samples placed under the hatch. However, once the store is opened the full extent of any bin to bin variation can be determined by sampling directly from a number of bins from each orchard

The samples should be assessed as previously described and the results compared to the last netted samples. Samples should be taken from the bins at regular intervals until all the fruits from that store have been graded and delivered to the customer.

Apple Best Practice Guide