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Harvest

Harvest timing for tree fruit crops varies based on the fruit type and variety. Various fruit maturity-testing methods are used to help determine when fruit are ready for harvest. Some methods also indicate which fruit will go straight to the market versus those that will be cold stored until marketing at a later time. Some types of fruit cold store better than others, whether in regular atmosphere (RA) or controlled atmosphere (CA) conditions. For storage purposes, some fruit are picked at early maturity with good quality and they are further ripened while in storage.

Individual orchard blocks of fruit should be evaluated and tested separately to determine maturity. To ensure optimal fruit quality, some trees may require multiple harvests. For example, fruit located at the canopy periphery on limbs that are well exposed to the sun will mature sooner than fruit on shaded limbs in the interior of the tree canopy. This is particularly the case for larger, older trees with extensive canopy volume.

A general seasonal benchmark that growers often use for estimating fruit maturity date is “days after full bloom” (DAFB). This reference can be especially useful if DAFB was recorded for harvest dates for that particular block in previous years. Depending on weather, the actual DAFB value may vary from 5 to 20 days or so from one year to the next. Ideally, maturity testing begins two weeks or more before estimated time of harvest and continues each week until harvest. Fruit firmness, soluble solids concentration (SSC) and starch content are among the primary tests performed at this time. Fruit size, taste, and skin coloration are also considered when making harvest decisions. Advancing maturity is indicated when values of each measurable parameter begin to change from week to week. In apples, for example, as fruit mature, firmness will decrease, SSC will increase and starch content will decrease (starch iodine test value, noted later, will increase).

The field horticulturist makes harvest decisions based on fruit volume, maturity, color, size and orchard history and then communicates these decisions to the warehouse. Fruit segregation, storage and marketing decisions are most accurately made through frequent and detailed communications between horticulturists, warehouse receiving personnel, storage and quality control personnel and marketing staff. Adjustments in harvest timing and the rate of harvest progress might be necessary to meet storage and marketing goals.

Click on the crop headings below to read about crop specific harvest information.

Apple

Apple Maturity and Harvest

Knowing when to harvest apples is critical not only for planning a labor schedule, but also for making decisions about whether the fruit will be sent to fresh markets or stored. Fruit harvested too early may have insufficient skin coloration, be too firm, have low SSC, poor flavor or be prone to storage scalds and bitter pit. Apple varieties mature at different times during the season. For the same variety, maturity can vary within the same orchard block and even within the same tree. For pre-harvest planning, days after full bloom (DAFB) can be used to estimate harvest dates. DAFB is only a general reference point and there may be a 5 to 20 day spread between the average harvest date and the optimal harvest date for a particular cultivar. To use DAFB as a guide, record the date of full bloom by block and cultivar in the spring, since full bloom may vary annually from one site on your farm to another.

There are several precise methods used to determine apple maturity. Maturity testing begins two weeks or more before estimated time of harvest and continues each week until harvest. The most important indicators driving harvest timing are firmness, starch content and background color. These are somewhat correlated to sugar content, acidity, flavor, aroma, texture, internal ethylene content (IEC), and potential storage life. Fruit skin color does not change significantly during storage, so if a fruit is picked without the correct color, marketability decreases. Also, if the fruit hasn’t achieved the correct background color, that fruit is most likely going to be too firm, starchy and be generally immature. In general, a combination of the presence of the desired background color, starch conversion of 25–35 percent, and firmness above 15 pounds will qualify for a good storage candidate. Candidate fruit for immediate fresh market sales would be those with the desired background color, starch ranging from 4.5 to 6.0 on the starch-iodine scale, sugar content above 13%, and firmness greater than 13 pounds. Keep in mind that there are set standards for specific varieties and markets. Links for the Washington State and the U.S. apple Standards webpages are found below:

As an apple starts to mature and ripen, it produces ethylene gas, known as the ‘ripening hormone.’ Testing for internal ethylene content (IEC) is crucial, because at some point during maturity, respiration will increase, and a surge of ethylene is produced. This is known as the respiratory climacteric. After the surge of ethylene is released, the apple will begin to senesce, losing quality, softening, and beginning to deteriorate. Essentially, there is a 7 to 11 day (+/- a few days) window of opportunity that exists in harvesting fruit of optimal quality, and that window needs to occur before the climacteric stage begins, as fruit quality will start to decline afterwards.

Testing for IEC involves the use of a gas chromatograph, making it a more difficult method of maturity testing that is normally performed by a specially trained laboratory technician. However, the other parameters already noted are more easily tested. Some testing methods are listed below. While some methods are older, they are still used and very reliable. Just as technology advances, so do the tools and methods used to determine fruit maturity.

Listed below are some of the primary changes in apple physiology that will occur as fruit become more mature:

  • Starch is converted to sugar
  • Seeds turn a darker color
  • Acidity decreases
  • Chlorophyll levels decrease
  • Respiration increases
  • Cell walls weaken, fruit begins to soften
  • Ethylene production increases

Maturity Tests

Starch Test: The stage of apple fruit maturity can be assessed by performing a simple starch-iodine test. Make up a solution of iodine using 10 grams iodine crystals + 25 grams potassium iodide in 1 liter of water. Avoid contact with the solution and its ingredients and be cautious when mixing and applying iodine solution. Cut an apple horizontally; apply iodine solution to the cut surface, draining off any excess solution. Rate the fruit’s reaction to the stain after 2 minutes. Portions of the flesh that contain starch will turn a blue-black color. In contrast, the cells that contain sugar will remain unchanged. The reaction to the iodine is temperature-dependent. Under cold conditions, the reaction will take longer. The pattern of starch disappearance is specific for each apple variety. For example, Delicious loses its starch in a fairly even ring, while Golden Delicious shows an uneven pattern. The common rating system is on a scale of 1 to 6 as follows:

1 = full starch (all blue-black)
2 = clear of stain in seed cavity and halfway to vascular area
3 = clear through the area including vascular bundles
4 = half of flesh clear
5 = starch just under skin
6 = free of starch (no stain)

However, not all apples are scored according to this scale. Researchers studying WSU’s new release, Cosmic Crisp™ WA38, use the Cornell maturity scale (ranging from 1-8). For more information on the maturity and storage of WA 38 apples, read the Good Fruit Grower article How to harvest and store WA 38 Cosmic Crisp™ apples.  More information regarding apple maturity can be found in the following links:

Pressure Test: Fruit firmness is another measurement reflecting the level of maturity. As fruit mature the flesh becomes softer. This is an important test because it also determines the fruit’s short or long-term storage capabilities without compromising the quality. Factors such as the presence of watercore or fruit size can affect the pressure readings. A fruit with watercore will give erroneously high readings. Any fruit with watercore should not be included in the test sample. Larger apples are usually softer than smaller ones from the same lot. Therefore, fruit samples for evaluation should consist of fruit relatively uniform in size and that are representative of the orchard block. Pressure tests are performed using a penetrometer. Although there are several devices currently on the market, the basic procedure is the same. For consistency, the same technician should perform tests for each fruit lot. To test, a disc of skin is removed along the circumference of the fruit from both the blush side and nonblush side to expose the underlying flesh. The penetrometer is plunged directly into the exposed fruit flesh (not through the skin) using even pressure lasting about 2 seconds. For apples, use the 11 mm tip supplied with the device and penetrate to a depth of 7.9 mm as marked on the plunger. Proper speed is the most critical part of this test. Applying pressure too fast is the most common way of getting an inaccurate reading. Finally, average the two readings to determine the single fruit value.

Soluble solids concentration (SSC): A refractometer is used to measure the soluble solids concentration of an extracted juice sample from the fruit. This is expressed as degrees or percent Brix and it is related to the fruit sugar content. As the fruit matures, starch is converted to sugar, and readings from this test will increase. The ideal readings will vary depending on the variety tested. There are several devices available including both manual and digital instruments. Measurements are made by squeezing a small amount of juice onto the device’s prism. If using a handheld device, hold the instrument up towards the light, look through the lens and read the percentage of soluble solids from the scale. Automatic instruments have an internal light source and sensor that delivers a digital value. The prism surface should be rinsed and carefully wiped off after each juice sample to prevent cross-contamination of juice from one sample to another. Temperature can also affect readings, therefore all samples should be at the same temperature when tested. Instruments can be calibrated by zeroing with distilled water and then using a 10% sugar solution (10 g of sucrose in 10 g of water).

Many factors can affect the SSC levels in fruit samples. Samples from heavily cropped trees will commonly have lower readings than those from lightly cropped trees. SSC values will be higher in years of reduced moisture availability, high temperatures, and high sunlight. SSC values will also vary between fruit from different locations on the tree. Fruit located in sun-exposed areas, where considerable photosynthesis is taking place, have higher SSC values while fruits in heavily shaded areas located inside the tree or on weak spurs have lower values.

Acidity: As fruits mature, their acid content decreases. Malic acid is the major acid in apple juice, and it plays a major role in flavor attributes. There are no state or federal guidelines for maturity based on acidity level. The amount of acid present is related to the variety and its stage of maturity. A drop in acidity is an indicator of advancing maturity. Measuring acidity is somewhat cumbersome and involves the use of common laboratory instruments such as a titrator or a buret. For best use as a maturity indicator, acid level should be recorded over a number of harvests to develop patterns and guidelines.

Color measurements: Color requirements differ depending on whether the variety is solid red, striped or partial red, red cheeked or blushed or whether the variety is green or yellow. Generally, for the varieties with red coloration, the commercial grade relates to the percent of the surface of the fruit that has a good shade of red color (more color, better grade). Red skin coloration is related to sunlight exposure.

Ethylene measurement: This type of test is very accurate, but requires a gas chromatograph and laboratory. Using a small gauge needle, the gas is extracted from the core of the apple to determine the maturity level. Before apples ripen and mature, ethylene is hard to detect, but as the apple starts to mature, ethylene levels begin to rise.

DA Meter: A new instrument developed by scientists at the University of Bologna, Italy, called the DA meter is used to measure the chlorophyll content in the fruit flesh. For each variety of apple, a characteristic DA index can be developed which includes a range of values related to the maturity of the fruit. As fruit mature, the DA value decreases. DA values are related to fruit maturity and this instrument may be used for nondestructive fruit maturity determination as compared to the destructive measurement needed with the starch-iodine test. It can be used while fruit are still attached to the tree or also on a commercial packing line.  For more information on the DA meter, read the Good Fruit Grower article An easy way to test maturity.

Dr. E. Kupferman noted that apple quality and maturity must be monitored throughout the storage duration to assure that apples of the highest quality reach the marketplace. (Excerpt from Delicious Harvest Maturity and Storage, 2010, WSU Postharvest Information Network webpage.)

Harvest

Once fruit is determined to be at the desired level of maturity, harvesting begins. Excellent harvesting practices are an essential part of the industry. Pickers must be well trained to ensure the quality of the apple is preserved from the tree to the warehouse. Rough handling is the most common way apples become damaged, and quality is compromised. Impact and compression injuries cause bruising. Picking wet or cold fruit increases the chance of bruising. Although all apples are subject to bruising, some varieties are more susceptible than others.

Automated technology is being developed to help preserve quality, and to address the problems of labor shortages and cost. Although a number of machines have been developed in recent years to aid workers and improve efficiency, the industry still depends on human workers to pick apples off the tree. Some of the new technologies include: Self-propelled platforms and remote controlled Bin-Dog for in-orchard bin handling. For more information on the status of mechanical apple harvesting technology, a good synopsis can be found in this recent Western Fruit Grower article The state of mechanical apple harvesting.

Once fruit is picked, and taken to a warehouse, additional sampling of lots may occur to determine if fruit will be packed immediately or stored. The goal is to provide consumers with optimal fruit quality year round. For this reason, storage capabilities will be conducive to the apple variety. Aside from market supply and demand, many apples survive long-term storage without compromising the quality, however certain varieties and cultivars are better suited for short-term storage. Visit our Storage link page for further details on storage.

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Pear

Pear Maturity and Harvest

Asian pears can be harvested near ripe and sold immediately for the fresh market. However, most European pears grown in the Pacific Northwest are stored and marketed over a period of time extending their availability for 6 to 8 months or longer. Long-term storage of pears can be challenging. Pears must be harvested at the right level of maturity to retain quality during storage.

Like previously noted for apples, fruit color, shape, size, soluble solids concentration (SSC), titratable acidity (TA) and firmness can be used to estimate maturity and harvest suitability. However, pear maturity indices are not as reliable or consistent as those for apples. The most consistently reliable measure is firmness which is measured with a penetrometer – the same as for apples (see apple section above).

Days after full bloom (DAFB) is a useful guide to give growers a “ball park estimate” for an approximate harvest date but this can vary from year to year. D’Anjou pears can range from 120 to 150 days; Bartletts can range from 110 to 133 days; Bosc can range from 130 to 145 days; and Asian varieties can vary from 122 to 150 days.

DA Meter: A new instrument developed by scientists at the University of Bologna, Italy, called the DA meter is used to measure the chlorophyll content in the flesh. For each variety of pear, a characteristic DA index can be developed which includes a range of values related to the maturity of the fruit. As fruit mature, the DA value decreases. DA values are related to fruit maturity and this instrument may be used for nondestructive fruit maturity determination. It can be used while fruit are still attached to the tree or also on a commercial packing line. For more information on the DA meter read the Good Fruit Grower article An easy way to test maturity.

Harvest maturity and the selection of storage regimes affect both the ripening and quality of pears during cold storage. Each variety has its own specific requirements. Note the following information regarding harvest maturity and storage regimes for common pears grown in the Pacific Northwest according to Meheriuk et al. (1988)

Bartlett pears destined for long-term controlled atmosphere (CA) storage are judged ready for harvest when their firmness reaches an average of 19.5 pounds pressure. Once this level of firmness is determined, the harvest window lasts from 4 to 7 days, depending on the weather. D’Anjou pears destined for long-term CA storage must be harvested when firmness reaches 15 pounds. Unlike Bartletts, background color, soluble solids and starch must also be taken into consideration for D’Anjous. And although variable between years, the harvest window for D’Anjous is usually around 7 to 10 days if they are to go into CA. D’Anjous are susceptible to storage scald, and friction burns to the skin. The use of plastic liners, especially in wooden bins, can reduce abrasion injury. Their quality is also affected by growing temperatures with best quality resulting when the average daily temperature is between 13.9C and 17.2C. Bosc pears for long-term CA storage are harvested when the firmness reaches 15 pounds and the appearance and finish are desirable. The harvest window for Bosc is about 7 days if they are to go into CA.

Like apples, most pears produce ethylene when mature and they also have a climacteric stage. Pears are harvested during the pre-climacteric stage when maturing has begun but the pear is not yet fully ripe. The D’Anjou pear produces very little ethylene, and is very sensitive to it, while Bartlett and Bosc varieties produce much higher levels of ethylene, in comparison to other pears. Fruit that is not conditioned this way will ripen slowly and not uniformly. The texture and flavor of nonconditioned fruit will be poor.

Pears are unique in the sense that in order to ripen, they require a pre-cooling or “conditioning” stage followed by exposure to room temperature. This is an essential part of pear maturity, as it jump-starts the internal production of ethylene, which then leads to the ripening process. Once fruits are conditioned and they are returned to room temperature, they will ripen normally. However, they can continue to be held in cold storage until a suitable marketing opportunity occurs.

For fruit harvested at the earliest maturity, Bartlett and Bosc will typically need cold storage for approximately 14 days, Comice 30 days, and D’Anjou at least 60 days. Actual times can vary somewhat from year to year. However, the traditional pre-cooling conditioning may be dramatically reduced by exposing pears to 100 parts per million of an external ethylene gas atmosphere in a sealed room at 68F for 24-48 h. For more information on harvest maturity and conditioning, read the Good Fruit Grower article Rethinking the chill requirement for pear ripening.

Asian pears are different from their European cousins. They do not require cooling to ripen and are harvested near-ripe. Generally they are not cold stored very long, but instead marketed quickly.

There are particular standards (both federal and for Washington State) required to market pears. Links for the WA state and U.S. pear standards webpages can be found below:

Careful fruit handling during harvest is essential in maintaining fruit quality for the customer. Rough handling can cause bruising or skin punctures that lead to pathogen rots that can show up in storage or later in the market. This can be avoided by proper management in the field and the packing house.  Dr. David Sugar, Oregon State University, discusses postharvest diseases in the 2015 video, Integrated management of postharvest diseases of pome fruits.

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Sweet Cherry

Sweet Cherry Maturity and Harvest

For growers, harvest timing is a balancing act between skin color, size, and flavor. Harvesting too early results in small size, poor color and poor flavor. Delaying harvest a few days can darken the color, increase the size, and boost the flavor. Fruit can increase in size 40% from the earliest they might be picked to full maturity. However, leaving unpicked cherries too long on the tree may result in soft fruit prone to injury, increased decay susceptibility, more shrivel, stem browning, and pitting. It can also add the risk of skin cracking from a sudden rain event or crop loss from hail damage. If the destination market is near, one may be able to risk harvesting more mature fruit. There are particular standards (both federal and for Washington state) required to market cherries. Links for the standards can be found below:

In comparison to harvesting apples, the cherry harvest season is fairly short and labor intensive. Color change is one of the most reliable factors in determining maturity for harvesting. Likewise, soluble solid content directly correlates with the color change. As the cherry darkens, the sugar content increases. Unlike apples and other fruits, ethylene does not play a role is cherry maturity. Although color may change slightly, other quality factors do not improve after harvest. A nine-year study on Bing cherries conducted at the Prosser Research Station during the 1980’s found that color change was not effected by temperature, or crop load. For more information, refer to Cherry Quality Research Summary. However, trees with a heavy crop load did have lower soluble solid content. Cherry firmness also correlates closely with skin color and can be used a maturity index. (Link)

Like apples, cherries are also susceptible to injury by compression and impact. Workers must be properly trained in harvesting such small delicate fruit. Picking cherries where the stem attaches to the branch or spur will decrease handling injuries. Because cherries have a high soluble solids content, they also contain a lot of water, which contributes to their firmness, and decreases the risk of compression injury.

Temperature also is a key element in maintaining quality since higher temperatures lead to higher respiration rates and increased fruit deterioration. Keeping the fruit cool will maintain firmness. If cherries are left in hot temperatures, they will soften, which in turns increases their susceptibility to injury. In the field, cherry bins should be kept in the shade to prevent over heating prior to transporting to the packing facility. Harvesting early in the day helps to ensure that fruit pulp temperature does not get too high prior to transport. Field heat should be removed from cherries by a hydrocooler in the field or at the warehouse. The longer the delay in removing the field heat by cooling, the shorter the shelf life of sweet cherries. For fruit destined for overseas markets, it is critical to get pulp temperature as close to 32F before shipping as possible. This is commonly done with forced-air cooling.

For a good review on factors influencing cherry quality (e.g., crop management, harvest date, environmental factors, harvest and postharvest practices), Growing quality cherries, by L. Long, Oregon State University, is helpful.

For a recent article on how to optimize cherry quality during export (e.g. modified atmosphere packaging, forced air cooling), read the Good Fruit Grower article Optimizing cherry quality during export.

WSU scientists are researching new technologies that could substantially reduce cherry harvest labor expenses through mechanical harvesting. Cherry picking is very labor intensive because of the small fruit size. Dr. Matt Whiting, WSU-IAREC, estimates that the current cost of labor harvest per pound is between 18-25 cents. Cost estimates using a mechanical harvester are projected to be reduced down to between 1 to 2 cents per pound, which includes the cost of the mechanical harvester.  For more detailed information please refer to:

Additional References

Washington State University