Maturity and Storage of Gala, Fuji, and Braeburn Apples
Apple growers in Washington State have been diversifying their new plantings to include Gala, Fuji, Jonagold, and Braeburn as well as the more traditional Red Delicious, Golden Delicious, and Granny Smith. Research on the maturation and storage of these varieties has been started by WSU and USDA scientists. I am grateful to Drs. Jim Mattheis, Eric Curry, and Steve Drake of USDA-ARS, Wenatchee, for use of their latest information. I have also included the results of scientific and industry trials from other fruit growing regions.
First a few observations and some philosophy:
- Timing of harvest must be based on the postharvest
requirements which include the intended length of storage
and shipment. Apples shipped great distances or stored for
a long time must be harvested at a less mature stage than
those consumed immediately after harvest.
- Growers often attempt to harvest new varieties too
early to take advantage of market conditions or too late to
wait for color, and fruit quality suffers. Some growers
apply large amounts of nitrogen to induce larger fruit size
which often reduces fruit firmness and shelf life.
- In the case of "new" apples varieties,
often there is an insufficient supply of fruit and
long-term storage is not needed. At this point there is a
broad range of acceptable maturity. As the supply increases
so does the need for storage and this range narrows.
- The age of the tree and the age of the wood upon
which a single fruit is borne greatly influence the
behavior of the fruit after harvest.
- The number of days of acceptable maturity ("harvest window") varies with the cultivar, season, and length of storage. Scientists understand little about what determines the harvest window.
Summarized below is what we currently know about the maturation and storage potential of apples grown in Washington. This information is preliminary and new studies will undoubtedly improve the information presently available. I urge caution in applying the results of research trials or industry practices performed with fruit grown under different climatic conditions, since this can often lead to poor results. I urge the use of small scale trials to determine the characteristics of the fruit you are harvesting.
New Zealand growers harvest Gala apples 4-5 times, picking fruit on the basis of ground color. Multiple picking appears to be essential to have fruit of good size, color, edible quality, and uniformity for storage.
Washington growers have harvested fruit with excellent edible quality when the ground color changes from green to yellow (in the white). Three to five pickings are required to obtain fruit of even maturity. The first pick should be sold immediately. Fruit from the next two picks have performed well in storage.
In one trial, Royal Gala harvested with white ground color had firmness of 17.5 lbs., 13.3% soluble solids, and 0.376% acidity. The starch rating was 3.6 on a 1-5 scale. Starch (2-3 on the 1-5 system) has been used by some researchers and orchardists to time harvest. If starch is to be useful, choose fruit of uniform ground color for testing.
Fruit destined for storage should be harvested with slightly green background color. Gala ripening begins at the stem end, with the calyx portion of the fruit ripening more slowly. Harvesting Galas based on a yellow ground color at the calyx results in fruit past its prime for storage.
Royal Gala export standards from New Zealand include a minimum blush of 66% red and a background of light green to creamy yellow. The blush is a marketing standard while the background color is a maturity indicator. The spread of maturity has been very wide and one method of standardizing maturity has been to harvest on the basis of background color. Unfortunately, fruit grown in different districts have been shown to be at different maturities. Fruit gown in southern districts (colder winters and hotter summers) are greasier, more yellow, and firmer than those Gala grown in areas with milder climates.
There is a possibility that the background color of Galas may be strongly influenced by nitrogen, similar to Golden Delicious (one of its parents). This would complicate the determination of harvest based on background color.
Fruit stored in CA tests had higher firmness and more acid than those stored in regular storage. Galas have not yet been subjected to different CA regimes. They respond well to 1% oxygen and 1% carbon dioxide at 32-34°F. Rapid cooling and atmosphere establishment are critical to the storage of Galas. No improvement in quality over regular storage can be detected if establishment of CA is delayed 14 days after harvest.
In Australia (1992), Galas harvested when the background color changed from green to yellow stored well for up to 5 months in 2% oxygen. Fruit harvested only two weeks later came out 2 lbs. softer and 56% of the fruit developed rots. Storage in an atmosphere flushed with nitrogen reduced rots on the late harvested fruit by half and resulted in firmer fruit with better flavor.
Potential Storage Problems of Gala
Rot--Late-harvested Galas are more susceptible to fruit rotting fungi than those harvested at white ground color.
Firmness and Acidity Loss--Softening can occur and acidity lost if fruit are not placed in CA directly after harvest. It is not possible to achieve good results if the CA is delayed. For example, Galas harvested early should not be held out of CA until enough Goldens are harvested in order to fill a room. Galas must be placed in CA immediately.
Scald--Scald has not been shown to be a problem.
Red color develops in Washington only late in the season and is highly dependent upon nitrogen level and light penetration within the canopy. Harvest maturity should be determined by ground color rather than red skin color. Timing harvest on the basis of red skin color is not effective for determining edible fruit quality.
Growers have noticed that Braeburn apples size rapidly during the last month of the growing season. Problems associated with fruit mineral content, reduced fruit size, and poor skin color can be reduced by delaying harvest until the fruit are mature as indicated by the change in ground color. However, delaying too long may increase the possibility of brownheart.
Braeburns exported from New Zealand must have 40% red color and only very small amounts of ethylene. Starch increases slowly during the harvest season. Firmness was not influenced by harvest date, although later harvested fruit softened more rapidly during storage. Red color does not reflect maturity. Background color, ethylene, and starch are important in determining maturity.
Braeburns grown in Washington change from a dull, dusty color to a brighter color as they mature. Growers have reported success by harvesting at a starch level of 2.5-3.5 (1-5 scale). Often the firmness of this fruit is 18 lbs. The first picking is not suitable for storage.
Potential Storage Problems of Braeburn
Bitter pit--This can be a serious problem with Braeburn, making calcium sprays very important. Balanced tree growth, fertility, and water management can reduce this problem. Braeburns are also susceptible to the type of bitter pit called lenticel blotch pit. Other internal disorders can develop due to mineral imbalances. Nitrogen nutrition appears to be important with this variety-too much nitrogen is harmful to fruit quality.
Brownheart, core cavities, and coreflush--Reports from New Zealand growers and industry representatives indicate that both incidence and severity of these problems are orchard and season dependent, with some orchards experiencing no affected fruit while others had over 90% affected. Less mature fruit and that with less blush had less brownheart. It has been noted in air-stored fruit and at times in fruit on the tree.
New Zealand studies have shown that fruit grown in orchards in their cooler districts have more brownheart than those from warmer districts. We are not sure how the Washington experience compares. Also, late harvested fruit have more likelihood of getting brownheart in storage.
In CA storage brownheart and cavities have occurred erratically. These symptoms also can be induced by methyl bromide fumigation.
Some Washington growers experienced severe problems with internal browning of Braeburns in 1993. There were two types of symptoms. When brownheart was found preharvest, the tissue was dense and dark, somewhat like brown watercore, but it was not associated with the vascular bundles. Cavities were not seen in this fruit.
When browning was seen after storage in Washington fruit, it appeared to be less dense and lighter in color. Cavities were seen in the flesh.
Washington observations have shown that brownheart is more predominant at the calyx end of the fruit. These are the last cells to divide. There may be some possible connection with use of growth regulators.
Scald--As in other varieties, if Braeburns are harvested too early, scald will develop if stored beyond 6 months in regular storage. DPA appears to reduce the amount of scald.
Mealiness--Poor texture has been associated with Braeburns after storage; however, the causal conditions as yet are unknown.
This variety requires several pickings. In Tasmania, Australia, it is recommended that the first picking include all fruit on all light-cropped trees in the block. The main picking includes normally cropped trees, except fruit on 1-year wood. The third and final picking includes fruit on 1-year wood, which are usually of lower quality. Only fruit from the second picking are of the quality to be stored.
Fuji produces less ethylene than other apple varieties so it is possible that the harvest window is longer than other varieties.
Measurement of soluble solids has not been a useful guide to maturity since seasonal variation and cropping levels cause large variations. For example, soluble solids can range from 12% in one year to 16% the next. Washington grown Fujis have ranged from 17-19% soluble solids. Flesh firmness is also not a suitable harvest indicator.
Growers begin harvest at the first sign of watercore in the most mature fruit on the tree or when starch has cleared at least halfway out through the cortex (3.5-4.0 on the Red Delicious AMP chart). Selection of individual fruit to harvest is determined by ground color. Tests in Washington State have shown that Fujis are ready for harvest when they start to lose their green background color. When the fruit reach a golden yellow ground color, some of the apples will have severe watercore, indicating that they are past the optimum for long storage. The severity of watercore has varied between years. Ground color appears to be a reasonable harvest measure, especially at the start of the harvest season. However, a portion of the fruit never changes ground color.
New Zealand reports only a very small change in ethylene over the maturity period. Firmness or starch have not proven to be good maturity indicators. Mild watercore decreases in storage and does not present problems, except in long-term CA when it is moderate or severe. Watercore and background color may be the best indicators of maturity. Red blush is not related to maturity. Watercore development is more rapid in southern areas of New Zealand.
Tests in Washington have shown that CA-stored Fujis were firmer, had more acidity and greener background color but no increase in soluble solids over those stored in regular storage.
Fujis stored in CA (2% oxygen with 2% carbon dioxide) resulted in apples almost 3 lbs. above those held in regular storage. There was no difference in soluble solids. In other preliminary tests, Fujis have responded well to very low oxygen storage (0.5-1.0%) with carbon dioxide at less than 1%.
Washington tests have shown internal damage to some Fuji apples when carbon dioxide has been held above 3%. Fruit which were more mature, stored in higher levels of carbon dioxide for long periods, have developed internal browning and cavities. Thus, carbon dioxide should be held below the oxygen level. Short-term carbon dioxide rise (3%) during pulldown should not be a problem unless it is not scrubbed. In tests at 1% oxygen, fruit held at 3% carbon dioxide or greater for 9 months had internal browning and cavities. Fujis have also shown internal chilling damage when held below 32°F if they had watercore. Slight watercore has not posed problems in CA, but moderate to severely watercored fruit has created problems for some packers.
Potential Storage Disorders of Fuji
Stain--In 1993, many growers experienced brown staining on the skin of Fujis. In some cases the stain was seen at harvest, but in many cases its severity increased over time. It appeared both on the sunny side or the shaded side of the fruit. It is most predominant on the sunny side of the fruit. The stain was brown with very sharp margins between affected and unaffected areas and did not penetrate into the flesh. DPA was not effective in reducing or preventing the stain. Fruit stored in CA appeared to be less affected than that in regular storage. Many factors may be implicated including: the 1993 growing season was unusually cool; trees are young; many growers have applied high levels of nitrogen; Washington growers have planted high coloring strains, etc. When fruit are very exposed, sunscald is a possibility.
The mechanism and cause of the stain are unknown. From the limited observations and testing there are a number of ideas worth further investigation. Limited nutrient analysis has thus far shown that the affected areas have higher amounts of magnesium in relation to calcium. Calcium sprays may or may not reduce this damage. Fuji fruit appear to have relatively low levels of calcium as compared to other fruits. It may be useful to avoid applying magnesium. Staining may be increased by high levels of nitrogen and some reports from Asia indicate that ammonium nitrate and urea may reduce fruit quality. Again, the mechanism and cause of the stain are unknown, thus it is not possible to make recommendations on methods to reduce future cases. Fruits of advanced maturity were more affected than those picked earlier. Fruit in storage developed more stain over time.
I have been in touch with Californian, New Zealand, and Chilean Fuji growers and researchers to determine the extent or existence of the problems in these areas. None of these locations has experienced this problem thus far.
Bitter pit--Fujis have not been thought of as a variety which is highly susceptible to low calcium disorders including bitter pit. However, fruit harvested in 1993 had a significant amount of bitter pit. Thus, it may be important to apply calcium to Fujis in the same manner as used on Braeburn or Goldens.
Scald--Fujis are susceptible to storage scald and DPA is needed to minimize scald. Very low oxygen levels or initial oxygen stress might be helpful in reducing scald. This was a commercial problem on certain lots in Washington in 1992. Harvesting at the appropriate maturity level reduced scald risk substantially. DPA did not reduce staining.
Rots--Fuji apples can develop storage rots since their thin skin makes them very susceptible. A prestorage fungicide should help reduce rotting. Late-harvested fruit are more susceptible to rots than earlier-harvested fruit. California growers report that Fujis which have had the stems clipped at harvest have less rot that those in which the long, thick stems can puncture or bruise fruit. Initial work by pathologists has implied that Fujis are more susceptible to rots than other apples.
Watercore--Severe watercore can develop in Fuji very early in the harvest season. Slight watercore in Fujis will disappear in storage. However, Fujis with moderate watercore may develop internal breakdown in long-term storage and those fruit with serious watercore are very prone to developing it in mid-term storage.
Coreflush and cavities--Internal core browning and cavities have been reported to be a problem with Washington Fujis. Browning begins around the core line and may even be present in some fruits at harvest. Dry, brown cavities develop in the flesh. Washington Fujis appear susceptible to internal damage from carbon dioxide (see Storage above).
Moldy core--In one test in Australia, 5% of the stored Fuji apples developed moldy core. In 1993, California-grown Fujis had major problems with moldy core. Some growers think that it was related to early springtime rains. As yet, moldy core has not been reported as a serious problem in Washington.
Shrivel--Since Fuji has a thin skin and produces very little natural wax, it is prone to shrivel, especially in storages with low humidity.
Dr. Eugene Kupferman, Postharvest Specialist
WSU Tree Fruit Research and Extension Center
1100 N. Western Ave., Wenatchee, WA 98801
Tree Fruit Postharvest Journal 5(3):10-15