What do packouts tell us about management?

The essential ingredient for increasing low consumer apple consumption in Australia is delivering a high-quality apple. As part of the Hort Innovation-funded Future Orchards® program, AgFirst’s John Wilton helps us to understand the myriad factors – from variety choice and maturity at harvest to storage technique – that affect fruit quality, and explains how growers can better manage them.

Compared to similar-income countries in northern continental Europe which consume between 17kg and 29kg of apples per capita a year, Australia consumes about 8kg per capita a year. This represents one apple per week eaten by the average Australian. This is similar to consumption in the United States but less than in Ireland, Poland, Canada, Russia and the United Kingdom.

The French, who are said not to eat apples during the summer when there are copious supplies of alternative fruit, still get through 24kg of apples per capita per year.

Asia generally has low per-capita apple consumption, with the exception of China, where per-capita fresh apple consumption approaches 12kg, South Korea where it is in the range of 7.4–11.4kg depending on crop harvest, and Singapore and Hong Kong, which are similar to Australia.

Incidentally, Japan – a wealthy nation with a protected apple market similar to Australia’s – consumes about 4kg of apples per capita. Because apples have to be imported into much of Asia, consumption tends to track income levels.

Storage pit losses can be heavy in varieties prone to the disorder, particularly where excessive potassium fertiliser has been applied and the foliar calcium program has been insufficient. Excess magnesium can also be a problem.

Here in New Zealand fresh apple consumption is about 18kg per person.

Apple consumption data from Europe and New Zealand suggests there is considerable scope to lift apple consumption in Australia. If Australian consumers could be persuaded to eat two apples a week instead of only one, the market size would double.

Quality and eating experience are key to lifting consumption

A study done in Western Australia as part of a vegetable and fruit program which surveyed consumers found that 23 per cent of consumers reported lack of variety and poor quality were barriers to purchasing fruit.

In the US, apple consumption was in slow decline until recently. In the past three to four years consumption has begun to increase from a low of about 7kg to about 8.5kg per person. Factors believed to be responsible for this market turnaround are the introduction of new and better varieties and improvements in storage that deliver a better product.

Not so many years ago the US market was dominated by Red Delicious – a red ‘plastic’ apple with tough skin and mediocre flavour and that was often soft and mealy but which sold largely on shape and colour because that was the message the advertisers were giving the consumer.

In recent years many new apple cultivars have entered the US market (some, such as Gala and Fuji, have arrived from overseas) so there is a much greater variety of apples available. (Incidentally, Gala has now replaced Red Delicious as the number one variety, and the relatively new variety Honeycrisp™ and other new varieties are creating a high-value apple sector in the market.)

Advances in storage technology (namely the introduction of Smartfresh™) and Dynamic Controlled Atmosphere (DCA) have resulted in a superior product coming out of long-term storage. Apples stored using these technologies hold their pressure much better and are relatively immune to storage disorders such as superficial scald. Being chemical free, DCA can be used for extending the storage life of organic fruit and apples destined for residue-sensitive markets.

The fresh market requires fresh, crisp, flavoursome apples. Adoption of these new storage tools has extended apple storage life and is delivering a superior product late in the fruit’s storage life.

These are the reasons the formerly static-to-declining US apple market has begun to show signs of growth in the past few years.

One fact of life regarding fruit storage is that, irrespective of storage technology, it’s all downhill in regard to quality once the fruit is harvested. Modern storage technologies slow down the process but cannot improve quality if it was not there to begin with.

Flavour, fruit firmness and crispness are key consumer demands

Surveys of consumers report that flavour is the number one attribute for repeat purchase, closely followed by fruit firmness and crisp or crunchy flesh.

Fruit firmness and a crunchy, juicy eating experience tend to be universal attributes across all cultivars.

Flavour attributes including sweetness, aroma and acid balance differ markedly among different cultivars, as does flavour preference among consumers. The key thing about flavour is that it must be characteristic of the variety, free of ‘off’ flavours and relatively uniform from one fruit to the next for a particular line.

Appearance is very important for the initial purchase decision but repeat purchase decisions depend on a satisfactory eating experience. These attributes are much more important than price to discerning consumers.

Advances in storage technology in recent years have improved the ability to supply high quality throughout the year in regard to fruit firmness, juiciness and crispness provided the fruit was harvested at an optimum stage of maturity for the intended storage regime and storage period.

Flavour behaviour is considerably more fickle to manage because, firstly, it is hugely dependant on how well the fruit was grown in the orchard. Secondly, each cultivar has its own optimum storage period for maintaining its flavour attributes, after which flavour tends to disappear. And, thirdly, the level of flavour development at harvest time also affects the flavour at packout.

For really long-term storage, such as is necessary in a marketing plan requiring fruit of a particular variety to be available up until the following season’s harvest, the fruit of some varieties may have to be picked before it is capable of developing its full characteristic flavour. Gala and Fuji are examples of varieties that retain their firmness and crispness well but lose their flavour much sooner.

Tree pit showing up before harvest can signal bitter pit problems in storage. It is usually associated with light crops and high tree vigour.

This is the reason the New Zealand apple industry has very good Northern Hemisphere markets for these varieties. New Zealand’s apples supply superior eating experiences to what is available from stored fruit that is already four or five months older than fruit from New Zealand. The strategy is to harvest these varieties a little later, once their flavour characteristics are better developed, then stabilise their stage of development with post-harvest management to maintain them in prime condition for the two to four months required for them to be taken to market and then consumed.

When you are in the business of long-term storage (such as for the Australian domestic market), fruit quality out of store becomes paramount, as does its behaviour between the storage facility and the consumer.

In recent years fruit storage technology has undergone continual development and refinement to reach the point where it is possible to supply top-quality fruit for a whole-year marketing period provided that the fruit quality harvest is capable of lasting the distance. Not all cultivars were created equal in this respect, as I have already mentioned. Therefore, a long-term storage program needs to focus on cultivars with long-term storage potential and on their stage of maturity at the time of harvest.

The cultivars we grow that have above-average storage potential include Cripps Pink, Braeburn, Scifresh and Granny Smith. Incidentally, on the New Zealand domestic market, one of our best-quality end-of-season apples happens to be a red strain of Braeburn which, because of its high early colour development, can be harvested at the commencement of starch degradation. Harvesting at this stage of maturity, with smart storage, together with this variety’s superb sugar-acid balance and flavour retention, makes long-term storage possible without running into Braeburn’s major weakness of soft mealy fruit that often results when lower-colour strains are harvested later once satisfactory colour has developed.

Stem puncture is a common form of handling damage.

Lenticel breakdown in stored Fuji was found in this instance to have been caused by low fruit calcium.

Storage technology today has reached the point where properly monitored and maintained storage facilities are capable of delivering a high-quality product with minimal storage-induced disorders. This means that most of our quality problems are closely linked to crop management in the orchard or problems between the orchard and the coolstore.

The main orchard factors that determine fruit quality are:

  • Growing-season weather
  • Crop load and fruit mineral balance
  • Harvest maturity
  • Handling damage between the tree and the coolstore
  • Adherence to cool chain protocols.

Growing season weather

Apples are grown across a wide range of climates in Australia, some of which could be considered marginal, particularly in regard to high summer temperatures which tend to induce a number of potential post-harvest problems. These include superficial scald, bitter pit and various forms of sunburn and heat injury.

Water stress, while positive for dry matter accumulation, tends to accentuate sunburn injury and calcium related disorders such as bitter pit and glassy core. Water supply problems occur frequently in the Australian climate so orchardists need to develop and use strategies to minimise the impact of water-stress fruit quality and post-harvest storage behaviour.

Crop load

Low crop load, such as from ‘off’-crop trees and high tree vigour, lead to calcium disorders and other post-harvest problems such as senescent breakdown.

Crop load has a huge influence on fruit-ripening and colour-development behaviour. Light-crop trees ripen fruit much earlier than trees with a normal crop. Excess crop loads delay colour development and lower eating quality and, because colour is delayed, fruit is likely to be harvested too mature for long-term storage.

Where there are problems with variable taste and eating quality in lines of fruit coming out of storage, this is indicative of variable crop loads in the orchard.

Uniform crop loading is a key to producing lines of high-quality fruit coming out of storage. The short-term solution is to overcome biennial-bearing and tree vigour problems. There are now many orchard management practices that can be implemented to reduce variability in the orchard.

Incidentally, remote sensing technology is advancing rapidly in packing lines and there are now machines capable of sorting fruit for internal defects and brix levels.

Mineral balance

Mineral balance in the fruit is implicated in a number of post-harvest disorders.

Nitrogen, calcium and phosphorus have the largest impact, followed by potassium.

In my opinion, when it comes to managing fruit quality, nitrogen is probably most important. The reason for this is that nitrogen status has a huge effect on fruit colour development and therefore harvest maturity. High nitrogen, particularly when matched with low phosphorus and potassium, supresses fruit colour development, leading to over-maturity at harvest.

Compared to leaves, the fruit is a very powerful nitrogen sink. Studies by L Cheng reported in the article ‘When and how much nitrogen should be applied to apple orchards’ (New York Fruit Quarterly, Volume 18 No 4, Winter 2010) on Royal Gala in upstate New York found that leaf nitrogen levels doubled from 1.5 per cent to 3 per cent when trees were supplied with luxury levels of nitrogen but fruit nitrogen content increased tenfold. The leaf nitrogen content increased in a curvilinear pattern with the rapid increase up to about 50kg N/ha which brought leaf nitrogen into the optimum range, then a slow increase as more fertiliser nitrogen was applied. Fruit nitrogen content had a straight-line response, rising from 0.03 per cent to 0.31 per cent as fertiliser nitrogen increased to about 250 kilograms per hectare. Once leaf and shoot growth terminated, total nitrogen fruit content accelerated rapidly, commencing about 90 days after budbreak.

The key to managing nitrogen status for high fruit quality is to have adequate supply in spring to drive spur leaf and bourse shoot growth, as well as set the crop, then run nitrogen levels down towards the deficiency range by harvest to maximise fruit colour development well ahead of harvest maturity so fruit can be picked at optimum maturity for long-term storage. Then, immediately after harvest, apply nitrogen fertiliser to restore tissue nitrogen to optimum levels. Because most of the spring growth’s flush and fruit-set nitrogen requirement comes from mobilisation of stored reserves within the tree, about two thirds of the fertiliser nitrogen requirement needs to be applied post-harvest. In mature bearing trees spring nitrogen applications should not be made after full bloom.

There is some data to indicate that supplication of a soluble phosphorus fertiliser around bloom may lift phosphorus status and increase yields.

Post-harvest rots can be a problem in storage if fungicide programs during the growing season are weak.

Potassium levels need to be adequate but not excessive because of the adverse effects potassium can have on fruit calcium levels. Incidentally, once adequate potassium status is achieved (usually about 1.2 per cent to 1.4 per cent in the leaf), application of further potassium fertiliser will not improve fruit colour but will adversely affect calcium and magnesium levels.

Apples with significant russet are unsuited to storage because excessive moisture loss through those areas of skin will cause shrivel. They should be graded out and sold quickly.

Harvest maturity

Harvest maturity has by far the greatest impact on fruit quality and determines potential storage life and the fruit’s behaviour once it moves into the market.

With the exception of the small percentage of the crop that tends to have advanced maturity by the beginning of the harvest window, fruit with the longest potential storage life will be that harvested early in the fruit maturation period. This is usually the first main pick. The fruit will have high fruit firmness, a low starch pattern index (SPI), some brix increase showing, and low or nil internal ethylene production.

Where fruit flavour is very important and an ethylene blocker such as 1-MCP is used, harvest needs to be a little later than that is considered optimum for long-term controlled-atmosphere (CA) storage regimes to ensure satisfactory flavour can develop.

Fruit that has been harvested too immature can fail to have acceptable flavour, and for varieties very susceptible to superficial scald, this also lifts the risk of this storage disorder occurring.

Relative to the quality problems fruit harvested at an advanced stage of maturity suffer, those associated with immaturity are minor.

Senescent breakdown, lenticel breakdown and core flush are all disorders found in late-harvest fruit.

Late-harvest fruit also suffers quality issues including soft fruit, mealy fruit and post-harvest rots – all factors which turn off consumers.

In the absence of ethylene blocker treatments (for example, 1-MCP), fruit removed from CA storage for any length of time quickly deteriorates through softening and an increased rate of ripening.

Handling damage

Bruising and stem punctures make up the bulk of handling damage injury. Often, pickers are blamed for handling damage. Their role in the problem is relatively minor, because every time fruit is moved it is liable to injury. Our experience indicates that significant injury (particularly stem punctures) occurs in the bin and along packing lines.

Rough orchard tracks, careless forklift operators and poorly designed packing lines being pushed beyond their capacity are responsible for most of the handling injury.

Harvest maturity is an important factor in the level of handling damage. Firm fruit harvested early in the harvest period suffers much less injury. Keeping ahead of maturity at harvest is the best way to minimise handling damage.

Shrivel

Shrivel is caused by excessive moisture loss during storage. This is often due to low humidity in the store, which can be viewed as a coolstore management problem.

Shrivel is also a problem when fruit with russet is being stored, because russet areas on fruit lack the waxy cuticle which is a moisture barrier that limits fruit moisture losses. Fruit with significant russet levels should be graded out of lines destined for storage and sold first.

Cool chain protocols

Maintaining the correct storage temperatures is critical for maintaining eating quality in stored fruits.

Varieties susceptible to soft scald, low-temperature breakdown and chill injury require step wise cooling to minimise these particular disorders.

Further reading

In the 12 years that the Future Orchards® program has been running its library has amassed a number of very good papers on pome fruit quality and storage, including ‘Storage technology for apples and pears’, written by Colin R Little and Robert J Holmes and published by the Department of Natural Resources and Environment (2000), which covers the fundamentals of fruit storage very well.

About the Author:

Horticultural Consultant, Agfirst, New Zealand