Tree Fruit Harvest & Storage Tips
Gary Moulton & Jacky King, WSU – NWREC Mount Vernon
In the case of most stone fruits, when the fruit has colored well and is beginning to soften, it is ripe for picking. A taste test will usually tell you when a given variety is ready. Peaches and nectarines usually soften first along the suture line, which runs from the stem to the blossom end of the fruit. Pressing this area slightly with your finger will help check for softening. Ground color break is another good indicator of when fruits are mature for harvest. Pick as the color break occurs –as the greenish skin ground color turns to yellow, or cream color in white flesh peaches and nectarines. Harvesting before this often yields immature fruit of lower quality which may never ripen properly. A frequent complaint in buying peaches at the grocery store is that the fruit was picked immature, and the result is often poor quality and a dissatisfied customer. Check for color on shaded areas of the fruit, not the sun-exposed side where red color may come early and hide the green.
Some of the newerpeach and nectarine varieties have been developed with high red color and firmer texture, making it more difficult to tell when they are ready to pick. Taste is still a good indicator of ripeness. Sample one, and if its level of sweetness is good even though the texture is a bit crunchy, it is probably ready. Fruits that you want to transport or save for display should be picked firm but mature. Fruit can be placed in a box lined with newspaper or other padding, with the stem end down. Avoid packing peaches and nectarines more than two layers deep or the bottom layer of fruit may be damaged. In a few days the fruit will soften and be ready to eat.
A more exact measurement for harvesting stone fruit uses the refractometer, an instrument that measures the percent of sugars -soluble solids- in a liquid (in this case the juice of the fruit). For those highly colored varieties with no visible ground color this is an effective method. Peaches and nectarines with readings above 10% will usually ripen well and taste good after they are harvested. When taking sugar readings there will be variation among the different varieties.
Some plums and apricots don’t ripen off the tree as well, so canning or drying are recommended rather than trying to store extra fruit. Both will do some ripening off the tree but the window between immature and mature fruit is small. Remember that storing most stone fruits will be short-term to very short-term. Enjoy them fresh while in season or choose a method to preserve them that works for you.
As apples ripen a hormone called ethylene is released by the fruit. This hormone acts on certain cells that separate the fruit stem from the spur on which it grows, called the abscission layer. As the fruit ripens, the cells in the abscission layer weaken causing fruits to eventually fall from the tree. In some varieties, like Akane and Gala, the bond is very strong and fruit hangs on the tree long after it is fully ripe. In other varieties, such as Gravenstein and Spartan, the bond of the cells is weaker and fruit tends to drop before fully ripe. Commercially a “stop-drop” can be applied to retard the hormonal process for a several days until fruit ripens.
There are anumber of methods used to check on harvest maturity in apples. A quick check is to cut a sample fruit horizontally and look at the seeds. Usually in later ripening varieties when the seeds become brown the fruit is ripe, but with early season apples, they may be ready to eat before the seeds turn brown.
As the fruit ripens, respiration increases (fruits breathe like we do) and the fruit begins to soften. At a certain point in its maturity, the fruit will go through a concentrated burst of increased ethylene and respiration, referred to as the climacteric. From that point the fruit is ripe and will reach senescence (die) and soften very rapidly. For storage we want to choose fruit that is mature but not necessarily at peak ripeness, before it has reached its climacteric. During the growing season, the leaves of the tree photosynthesize (take in carbon dioxide plus water plus sunlight) to produce sugars, which are transported to the fruit and stored in the form of starch. As the fruit begins to ripen, usually from the core outward, the starch is converted back to sugar.
When a sample fruit is cut horizontally through the core and sprayed with a mild iodine
solution, the iodine turns the cells containing starch dark, but does not color those
cells containing sugar. This is the starch test, which indicates visibly the stage
of ripeness that a fruit has reached.
It is one of the easiest and most useful indicators available for the home orchardist. When only the area of the core is clear of starch, and the rest is dark, the fruit is usually unripe and immature. Fruit that you want to store should be picked when one-half to three-quarters of the sample cross section area is clear of starch. Usually at that point it has developed enough sugar to taste good (mature), and still retains sufficient starch to continue developing in storage (pre-climacteric). If most of the cross section of the fruit is clear of starch, it is too ripe for long storage and should be consumed at once or stored short-term only.
When using the starch test as a harvest indicator, test one or two sample fruit that look ripe for picking. If the test shows that they are ready, pick just those fruit that are like the ones that you tested, in terms of how much red color they have (in red varieties), and the green ground color turning to yellow. Do not pick fruit that are too different from the specimens you checked, or you will end up with a lot of fruit that is not mature. Fruit that has the best sun exposure, in the tree tops or on the south side of the tree, or in young trees with open branches, will normally ripen first. Pick those and come back a few days later and check the ones that are not ready at the first picking. Pre-mixed iodine solution for testing is available in 1-quart containers for home orchards, which should be enough for a couple of seasons. It can be ordered from orchard suppliers. Be sure to discard iodine treated fruit.
Another tool which tests fruit firmness is the pressure tester (see the section on pear maturity.) It is one of the primary tools used to test European pears. The only difference is that a larger probe is used for apples. This tool shows how firm or crisp a fruit is and how quickly it is softening.
An important fact to remember is that while those varieties that ripen later in the season are better suited for long-term storage, for each specific variety the earlier harvested fruit will store the longest. For example, Melrose typically ripens from the 10th to the 24th of October. The Melrose fruit that were picked earliest, on October 10, will store better and longer than the ones picked later on. The reason for this is that fruits from the later picking of a given tree have less starch, are softer, and are closer to or past the climacteric and will therefore decline more rapidly in storage. It is interesting that many home orchardists store the last picked fruit when the opposite should be the case. The first fruits of a variety to be picked should be the ones stored.
European pears divide into two basic categories: fall pears, that do not need a storage period before they are ready to use, and winter pears, that will not mature properly unless they are given a resting period in cold storage immediately after picking. The fall pears are earlier ripening varieties such as Bartlett, Clapp Favorite, and Orcas, while those that ripen later, such as Bosc, Comice, and Highland, are winter pears.
In either case, both fall and winter pears still look “green” at the time they are ready to pick. If you wait to pick your pears until they look ripe, with yellow skin color, they will be soft and soon rot in storage. In addition, since most pears ripen from the inside out, if left on the tree to ripen, many varieties will brown at the core–in other words, they are overripe in the middle. This is variety dependent but is particularly common in most fall pears. The Orcas pear is one fall variety that has not been plagued with this condition and ripens fairly well on the tree. However, if you want to store pears for a month or more, letting them ripen on the tree won’t work. The earlier harvested fruit on a pear also stores the best for a given variety, and like apples the later season varieties (winter pears) have the longest storage potential.
How do you know, then, what is the right time? Commercial and research orchards use a hand-held pressure tester. This is an instrument with a spring scale that registers the amount of force (usually recorded in pounds) required to push a metal probe of specific area into the fruit. This measures the firmness of the fruit, and for pears it is quite a reliable indicator of the fruit softening as it ripens. However, the tester is relatively expensive, about $150, not very practical for most people with only a couple of backyard trees. It can also be used to test your apples.
The best guide for the home orchardist is this: when most pears are ripe, the stems will easily separate from the spur (at the abscission layer) when the fruit is lifted. If you have to tug and pull to get the pear off, it usually is not ready. After picking, fall pears can be kept on a shelf at room temperature until ready to eat – when yellow color develops and the fruit begins to soften. Fall pears can be stored but usually do not keep for more than 4–6 weeks, Many people use their fall pears for canning and drying. Winter pears should be put into some kind of cold storage (below 40°F, down to 33°F) for at least 3 weeks. After that period, you can start to bring out fruit as needed to soften up at room temperature. At first it may take 5 to 9 days before the pears are ready to eat; later on a couple of days at room temperature may be long enough.
One other tip is to record the day of harvest for your trees from year to year; usually
they will be within a week of that harvest period each year. Start testing the fruit 1–2
weeks before the anticipated harvest date and before long you will be proficient at
Asian pears are similar to apples, in that they ripen on the tree and do not need an additional storage period to mature before they are ready to eat. In picking them, look for the color break, when green skin color starts to change to yellow. This is easily seen in yellow skinned varieties, but even with the tan and brown skinned fruit there is a distinct change from greenish to a golden undershade as the fruit gets ripe. Taste a sample fruit for sweetness, and if it is ready, pick any others that look similar. A refractometer (described above) is a more exact method for sugar testing. Asian pears can be stored but sometimes develop a strong, winy taste if kept too long. When storing Asian pears loose in a box, it is a good idea to clip the stems short, because the stiff stems can puncture and damage the fruit. Fruits that rub will often become dark at the rub points.
For long term storage of any fruit, the key words are cool and ventilated. Cooling slows down the fruit respiration, which slows down senescence. Ventilation keeps ethylene and carbon dioxide from building up to damaging levels. Some people use old refrigerators set aside just for keeping fruit. If that is impractical, choose an area with low heat that does not go below freezing. A garage or shed, unheated porch, or dry basement area are possible locations. Avoid direct sunlight or areas with a wide range in temperature. Avoid confined unventilated areas. Fruit can be packed in ordinary boxes lined with newspaper or other padding. Some people use perforated plastic box liner bags (available from orchard suppliers) to prevent fruit from drying and shriveling in long storage. Plastic bags without holes for ventilation should not be used as they can cause buildup of trapped ethylene, which will speed up ripening and shorten storage life, while excess moisture contributes to rot. Avoid storing fruit with open blemishes as they will be a focus for rot. Check periodically for rotten fruits and remove them at once. The old timers knew what they were talking about when they said that “one rotten apple spoils the whole barrel”. If picked at the proper time and given good storage, many of our best apples and pears can be enjoyed for months after the harvest season is over.