Why Do Your Stored Apples Shrivel and Your Pears Rot from the Core?

Harvest maturity versus eating ripeness, the abscission layer in the stem, and a simple starch test you can do at home

Every autumn the same scene repeats in gardens: a grower checks the calendar, sees the end of September or the middle of October, grabs a ladder and picks every apple and pear in one go. Two months later the cellar delivers two big disappointments. Some of the apples have wrinkled, leathery skin with bitter brown spots beneath it. The others (mostly pears) look beautifully yellow, but when cut open the flesh around the core is completely brown and mushy.

The cause is neither a poor cellar nor an orchard disease, but a harvest date that was off by just 7 to 10 days. With apples and pears there is a thin line between two terms that differ greatly in late varieties: harvest maturity and eating ripeness.

If you want fruit with top flavour that stays crisp and juicy in the cellar until spring, stop following the date on the calendar and learn to read the tree itself – from the hormonal signals in the stem to the conversion of starch in the flesh.

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1Harvest maturity versus eating ripeness: why fruit keeps “breathing” after picking

To know when to put the ladder against the tree, you need to tell two stages of the fruit apart:

With berries (strawberries, raspberries, currants) and stone fruit the two stages almost overlap – for apricots or peaches the gap is at most 2 to 3 days, needed for transport. With pome fruit the differences are large and depend on the group of varieties:

• Summer varieties of apples (such as 'Júlia', 'Yellow Transparent') and pears ('Clapp’s Favorite', 'Williams') have a very short gap between harvest maturity and eating ripeness – the two almost coincide. This is naturally soft fruit that should be eaten or processed right after picking.
• Autumn and winter varieties show the largest gap. The popular 'Gala' is picked in mid-September, reaches eating ripeness in October and keeps in storage until February. The typical winter variety 'Braeburn' is picked in late October, but only reaches its best flavour (eating ripeness) in March and can be stored until June.

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How can a winter apple ripen only in the cellar? Apples and pears are so-called climacteric fruit. After picking, they start producing ethylene (the gaseous ripening hormone) on their own, and their respiration rises sharply (the climacteric rise). During summer the tree stores starch in the fruit – it is tasteless and does not dissolve in water. After picking, enzymes (amylases) gradually break it down into simple sugars: glucose, fructose and sucrose.

This is where the main storage trap lies:

2The abscission layer in the stem: why you should never pull fruit off

The best-known practical test of harvest maturity is checking how easily the stem separates from the branch. From the point of view of plant physiology there is no magic in it – it is a precisely controlled hormonal process in a spot called the abscission layer.

How does it work? All summer, while the seeds develop in the core, the young seeds produce plant hormones called auxins (mainly indole-3-acetic acid, IAA). Auxins flow from the seeds through the stem into the branch. While this flow is strong, the cells where the stem joins the branch stay firm and flexible and withstand the weight of the fruit and the wind.

Once the seeds mature (turn brown) and the fruit reaches harvest maturity, auxin production drops sharply while the levels of ethylene and abscisic acid (ABA) in the fruit rise. This shift in the hormone balance is the tree’s signal: “The seeds are ready, the fruit can go out into the world.” In the tissue at the base of the stem, the enzymes cellulase and polygalacturonase become active and dissolve the middle lamella between cells in a thin layer across the stem. A cork scar forms and the fruit is then held only by the vascular bundles.

3Four more signs that must agree with the stem

An experienced pomologist never relies on a single sign but judges a set of indicators together.

How to read the starch test result

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4The special case of pears: why a pear ripened on the tree is almost always ruined

For pears (Pyrus communis) a strict rule applies that separates successful growers from unsuccessful ones:

Autumn and winter European pears are picked only at harvest maturity and are never left to soften on the tree.

The only exceptions are some summer varieties, where harvest maturity and eating ripeness almost coincide, and Asian pears, Pyrus pyrifolia (nashi), which ripen on the tree.

Why does a pear rot from the inside on the tree? A pear ripens physiologically from the core outwards towards the skin. If you leave an autumn or winter pear ('Conference', 'Lucas', 'Bosc') hanging until it softens and turns yellow, the tissue around the core has long since collapsed from lack of oxygen and an excess of ethylene. The cells have died, acetaldehyde and ethanol have been released, and the typical brown, mushy mass has formed (core rot). In addition, hard stone cells (sclereids) build up around the core during the long stay on the tree and feel gritty between your teeth when you eat the pear.

To pass from harvest maturity to eating ripeness (starting ethylene production and softening to a buttery texture), winter pears need cold induction – they have to spend several weeks in the cold.

5Picking technique that decides months in the cellar

Even perfectly timed harvest maturity can be spoiled in the last five minutes.

Conclusion

All year we spend dozens of hours on pruning, feeding, fruit thinning and protection. It would be a great pity to lose the result of that work in the final week just because we followed the date on the calendar instead of the tree’s physiology and confused harvest maturity with eating ripeness.

Once you learn to read the interplay between the loosening of the stem, the change in the ground colour of the skin and the gradual retreat of starch, you will find that every variety in your garden tells you exactly when the time is right. Your reward for patience at harvest will not be shrivelled apples and rotten pears in November, but full crates of fragrant, juicy fruit that keeps its true varietal character until spring.