Post storage grading of fruits
Once a store is opened fruit should be assessed against customer specification requirements and graded to deliver optimum return to the grower.
- Before a store is opened, all available information should be assessed.
- Pre-storage assessment and store monitoring data will be vital in determining the potential marketing outlet.
- Only fruit with the potential for a good grade-out will be worth packing for a multiple retailer (supermarket) outlet.
- Poor raw material may end up producing a negative return if allowed to enter the higher cost operation required for multiple customers.
Depending on which outlet the fruit is intended for i.e. multiple, wholesale, or processing, assessment will need to reflect customer specification.
- All standards will involve visual, textural, internal and organoleptic characteristics.
- Multiple standards will be the highest for all quality characteristics, but processing will still require fruit of good shape and freedom from internal problems including under skin bruising.
- The minimum standard for any product sold into the wholesale or multiple sector must meet EC (Defra) standards.
- Visual standards cover shape, colour, and the amount of bruising and blemish, freedom from pests, diseases and foreign matter.
- Textural standards recognise that good textured fruit are generally firm. Firmness measurements are a standard requirement for all multiple customers, and all now use an electronic penetrometer also known as Fruit Texture Analyser (FTA).
- Good textural quality will also be associated with fruit tissue in which cells break under pressure from the teeth thus releasing juice and flavour. In contrast in fruits that are described as ‘mealy’ or ‘floury’ the cells will separate under pressure from teeth and will fail to liberate juice. Currently there is no instrument that is equivalent to the penetrometer that can be used to indicate an acceptable texture in soft fruit.
- Internal standards require freedom from disorders such as bitter pit, low temperature and senescent breakdown, carbon-dioxide injury, etc.
- Organoleptic standards are concerned with levels of sugar (oBrix) and acidity and freedom from any taints or off-flavours. Overall acceptance by taste panels will be part of some customer specifications.
- All consignments of fruit supplied to multiple retailers must be traceable. They should be from an approved source and an Assured Produce number is required where the Red Tractor logo is used.
- Also individual multiple retailers have different audit requirements on top of Assured Produce that need to be achieved. For example, Tesco has its Nature’s Choice standard, M&S has Field to Fork and Waitrose has adopted LEAF.
- As soon as the store is opened an assessment of the fruit from each orchard should be undertaken. In practical terms this may have to be an on-going process due to access to fruit from particular orchards.
- Ideally 100 apples taken from a minimum of 20 bins from each orchard should be assessed and sized in 5mm bands.
- Assessment should be made against the intended customer specification.
- Assessments for fruit in each size band will take into account all the visual, textural, internal and organoleptic criteria indicated above.
- This then enables fruit to be allocated to different customers much easier before it is graded.
- Once an assessment report has been made, and customer target confirmed, levels of staff on the inspection tables can be decided and any instructions given regarding particular defects.
- On-going assessment of raw material from each orchard should continue to take place on a daily basis to confirm the status of the fruit prior to grading. The results should be recorded and entered into a raw material assessment repor.
Temperature of fruit during packing
- Ideally packhouses should be air-conditioned with a working temperature around 10oC.
- The temperature of fruit at packing may influence the level of grader damage as fruit passes along the line.
- Some varieties, such as Discovery, are more susceptible than others to grader damage.
Time between harvest and packing
- An interval between picking and packing will be required to reduce grader damage and will be influenced by variety and weather at picking time.
- Heavy rain prior to harvest will result in turgid fruit, which will bruise easily if graded too quickly.
- Depending on the grading equipment, it may require up to a week for fruit to reach a condition allowing satisfactory handling, without drastically reducing grade-out.
- If uncertainty about a batch exists, it would be good practice to either grade a small batch or, if possible, simulate fruit grader movement to evaluate the probability of damage occurring.
- The later varieties like Braeburn require a period of storage before fruit is eating at its best, therefore regular sampling is required to decide when fruit is ready for grading
- Selection of equipment equal to the task should be part of any assessment before committing apples to a packing line.
- The scale of operation will influence the equipment decision.
- Large packing operations depend on large volume throughput for cost-efficient operation.
- Small/medium sites will generally grade and pack as part of one operation.
- Large operations will generally carry out the grading and packing in two parts.
- Raw material should be off-loaded by water flotation into water flumes, passing onto the grading line where fruit size, colour and defects are sorted either with human selection or by high specification camera.
- Fruit is then returned to designated water flumes before, collection and return to bins.
- Bins are then returned to cold store, before returning to the packing line.
- The intended customer outlet i.e. multiple, wholesaler or processor may also influence the decision on grading.
- Lower value outlets may not justify the use of expensive high technology operations.
Dry tip or water flotation
- Dry tip operations will only be justified in a small operation. Where dry tipping is used the tipper should always be of the type unloading from the top of the inverted bin, reducing movement of fruits within the bin.
- Other types of tipper where fruit is down loaded from the bottom cause fruit to be bruised, blemished or punctured by stalks. In addition, any rots within the bin will break up causing rot residue to infiltrate the packed product.
- Dry tipping should make use of a water cleansing system (spray bars fitted in line using potable water) to remove where possible any undesirable foreign matter (rot residue, dust etc.).
- Ideally water flotation systems will start with automated bin down loading, allowing fork-lift truck loading of the equipment and automatic selection (usually from stacks of three, on a roller feed entry system) of fresh bins into the water flotation system, reducing unnecessary labour input. Empty bins will be collected and removed in the same manner.
- Once down-loaded the fruit will travel in water flumes to the grader.
Optical sizing and colour selection
- Sizing has moved on from historic rising bar systems and weight graders that can be difficult to calibrate accurately when fruit density and shape varies. Both historic systems fail to deliver size grading which is accurate enough for today’s customer requirements.
- Even sizing within a container is vital.
- Optical sizing by camera is the current best practice.
- In many pack-houses colour selection is now carried out by camera. The latest technology will allow colour streaming which enables a more uniform colour presentation within the final pack. This in turn allows an efficient packhouse the opportunity to deliver to the retail customer a top quality pack, and the grower the maximum possible colour grade-out within the specification.
Quality selection by camera technology
- Quality selection in most packing operations is currently still achieved by human selection.
- This operation depends on the physical removal of fruit by grading staff on the packing line onto a moving belt. The use of electronic wands also requires human selection, but allows automatic transfer of below specification fruit out of the line into a designated area.
- Quality selection cameras allow computer aided recognition of defects, reducing the need for large numbers of personnel on the grading tables.
- Currently this technology works well on the continent with their varieties, but has limited use in the UK.
- There are systems operating and these will continue to be improved. Current systems working in the UK have reduced the need for personnel on the grading line to a minimum.
- At specific stages human involvement is required for the removal of rots but generally any human quality selection can be confined to the final packing stage, where any minor defects which have passed the camera can be removed.
Non-destructive (infra-red) texture selection
- One of the most difficult problems to deal with in any raw material is the uncertainty of variable textured fruit. That uncertainty often results in fruit being assessed as unsuitable for multiple use.
- Non-destructive texture selection is currently only at the developmental stage for apples but inevitably will play a part in the future, making selection from variable raw material possible.
- Recognition of under skin bruising and internal disorders may also be possible in the near future.
Gentle and efficient movement of fruit through the grading and packing system
- The Loughborough University study for ADAS (1986) demonstrated that packing line grading damage could reduce marketable fruit by 38% – 49%.
- Most packing lines have improved considerably since the 1986 study, but even on the smoothest system damage can occur if people and equipment do not handle fruit with care.
- Packers should carry out regular ‘step testing’ to ensure equipment is calibrated to give the best possible performance.
- To step test, a sample should be gathered and assessed for bruise/blemish and introduced to the grading line. A proportion of fruit is removed at each step and left for 24 hours before being assessed. Results are compared with those from the original sample. This should identify where poor performance areas exist on the grading line.
- There is an electronic apple now available which can be used to identify ‘hot spots’ in a more scientific, albeit more costly, way.
Relationship between size and weight
- Depending on the density of the apple (and this will vary within as well as between varieties) size/weight relationships can vary markedly.
- This can cause considerable problems with accurate size and targeted weights in final packs.
- There are always ‘difficult sizes’ within any range of sizes. For example, where the standard size has been 65-70 mm in Cox, a reduction in size range to 63-68 mm will often make achieving the target weight impractical where fruit density varies on a regional basis.
- The lower density of Discovery will dictate lower pack ‘target weights’ than, for example Cox.
- This will impact on increased haulage charges per lb/kg of fruit.
- Delivering accurate size and consistent pack weights will depend on optimising performance where a weight grader is used.
- Optical cameras for sizing will improve sizing accuracy, but fruit density will still influence pack weights particularly where packs are by ‘count’ but a minimum pack weight is still required.
Calibration of equipment
- Delivering accurate size and consistent pack weights will depend on regular calibration of any grader but particularly where a weight grader is used.
- Fruit should be monitored regularly to assess accuracy, and the grader re-calibrated where necessary.
- Delivering accurate grading performance is vital for any pack-house intending to stay competitive.
- Under-grading will put customer service levels at risk resulting in possible de-listing.
- Over-grading will result in reduced financial returns to the grower and loss of potential business for the packer.
- It is therefore vital that quality controllers assess the performance of the grading line on a regular basis. This should be done at each step of the production line.
- It is vital that all product is assessed i.e. Class 1, Class 2 and any out-grade fruit. This is particularly important, as it is very easy to over-grade when attempting to satisfy a demanding retail customer.
- All packhouses must recognise the customer base is grower and retailer together if they are to succeed.
- Best practice should deliver accurate grading acceptable to the grower and retail customer.
- Staff training is a critical part of packhouse performance.
- Training should always be targeted at the level required. For example, all staff must have induction training to take account of site health and safety issues.
- General training should be given to ensure each worker has the level of skill required for his or her tasks.
- Grading staff need to be fully conversant with customer specification requirements. This may be achieved by training in the aspects of the specification which are key to the task involved.
- All packhouse staff should be aware of grading standards and should be prepared to remove defective fruit at any stage of grading rather than rely on others to do so.
- Supervisors will need to be conversant with all aspects under their control.
- Motivation is an important factor.
- Personnel will respond to various motivation factors.
- Performance pay may be considered to aid motivation.
- An understanding of the product and its destination is also a key factor in improving performance.
- Involving personnel at all levels, keeping them informed of overall performance and critically sharing any success with them will vastly improve the overall performance.
- Communication is the key factor involved in any performance motivation.
On-line process controls
- These are dealt with in detail in the section on post-storage packing and distribution of fruit.