What Fruits Emit Ethylene Gas for Ripening?

Many fruits ripen themselves with a colourless, odourless gas they release into the air, and the biggest producers are the fruits that keep ripening after they’re picked. That same gas drifts to nearby produce and speeds its ripening too, which is why a fruit bowl or crisper drawer can ripen or spoil things faster than you’d expect.1Bluapple. Why Does Produce Spoil So Quickly in the Refrigerator? Fruits that only ripen on the plant, like citrus and grapes, give off little, so the gas does little for them once picked.

The Fruits That Give Off the Most Ethylene

Ethylene is a plant hormone that exists as a gas at room temperature.2Journal of the Japanese Society for Horticultural Science. Ethylene Biosynthesis and Perception in Fruit Plants use it at many stages of life, from sprouting seeds to ageing leaves and flowers to ripening fruit.3Journal of the Japanese Society for Horticultural Science. Ethylene Biosynthesis and Perception in Fruit Fruit makes very little before ripening starts, then production rises sharply once ripening begins.4Acta Horticulturae. Role of Ethylene in Fruit Ripening

A wide range means output changes a lot as the fruit ripens, and the banana’s range reflects output climbing as the peel turns yellow. A hard green banana gives off far less than the same banana once yellow. Ripe fruit usually emits more than hard fruit of the same kind, and bruised or cut fruit can emit more than whole fruit, which comes up later. Even within one fruit, varieties differ in how much gas they make, as with different apple and peach types.9Journal of the Japanese Society for Horticultural Science. Ethylene Biosynthesis and Perception in Fruit A heavy emitter isn’t necessarily a fruit that suffers from the gas. Some are fairly tolerant of it, while a leafy vegetable that makes almost none can be badly affected.

Why Some Fruits Ripen After Picking and Others Don’t

Fruits that keep ripening after picking get a burst of breathing and ethylene output at the start of ripening.10Journal of Experimental Botany. Non-climacteric fruit development and ripening regulation: ‘the phytohormones show’11Journal of Experimental Botany. Non-climacteric fruit development and ripening regulation: ‘the phytohormones show’ Fruits that only ripen on the plant, such as strawberries, grapes and citrus ripen mostly through another hormone, abscisic acid.12Journal of Experimental Botany. Non-climacteric fruit development and ripening regulation: ‘the phytohormones show’ Even these use small amounts of ethylene alongside other hormones.13Horticulturae. Recent Advances in Hormonal Regulation and Cross-Talk during Non-Climacteric Fruit Development and Ripening

In gas-driven fruit, ripening is a chain reaction: a little gas triggers the fruit to make more, which pushes ripening along faster. That’s why such fruit can seem to stay hard for days and then soften over a short stretch. Fruit that ripens mostly through other hormones changes more gradually, with no sudden acceleration.

Inside a fruit that keeps ripening after picking, starch turns to sugar, acids fall, and the flesh softens as cell walls loosen. Aroma compounds build too, which is why a ripe peach smells like a peach and a hard one barely does. A fruit that hasn’t started this process when picked can’t be pushed through it by waiting. Fruit that only ripens on the plant may soften or wilt off the plant but won’t get sweeter, so a sour orange stays sour however long it sits.

The lines blur in places. Guava, melon, Japanese plum, Asian pear and pepper can behave either way depending on variety.14PubMed Central. The fading distinctions between classical patterns of ripening in climacteric and non-climacteric fruit and the ubiquity of ethylene—An overview Some melon varieties fall in between, so melon ripening is a sliding scale rather than two boxes.15PubMed Central. Comparative transcriptional profiling analysis of developing melon (Cucumis melo L.) fruit from climacteric and non-climacteric varieties Melons that ripen the gas-driven way tend to slip off the vine on their own and smell sweet, but varieties lacking the burst show neither drop-off nor aroma.16Makara Journal of Science. Differential Gene Expression of Ethylene Biosynthesis and Signaling Associated with Climacteric Behaviors in Indonesian Melon

At the store, that means picking strawberries, grapes and citrus ripe, since they won’t sweeten on your counter. Hard avocados, pears and bananas can be bought unripe and ripened at home. For a cantaloupe-type melon, smell and a stem that has slipped help you judge ripeness, though some melons sold ripe won’t improve on the counter.

Which Produce to Keep Away From Emitters

In an enclosed produce drawer, ethylene builds up and speeds ripening of everything nearby.17Bluapple. Why Does Produce Spoil So Quickly in the Refrigerator? Gas released into open air disperses, but a shut crisper drawer or sealed bag lets it concentrate around the produce. Storing produce too close together is one of the most common causes of spoilage at home,18Real Simple. The Secret to Storing Every Type of Fruit and Vegetable so emitters should be separated from produce that is sensitive to the gas.19Have A Plant. About The Buzz: Certain Fruits and Vegetables Should Not Be Stored Together?

Leafy greens and lettuce yellow and wilt faster near ethylene. Broccoli yellows, cucumbers soften, and carrots can turn bitter. Unripe kiwis and bananas ripen faster near apples, and cut flowers wilt sooner beside a fruit bowl. If you see these changes, check what shares the drawer.

A simple layout helps. Use one crisper drawer for apples and pears and another for vegetables. Keep bananas, avocados and tomatoes on the counter, away from the fruit bowl, and store potatoes apart from apples. Open-weave or ventilated containers let gas escape, as does opening the drawer now and then. Check drawers weekly and remove overripe pieces, which emit the most.

Bananas have their own tricks. Separating them from the bunch slows ripening.20Mess Brands. Ethylene Producing Fruits and Vegetables: Chart & Storage Guide Hanging them keeps them from bruising and from touching other fruit. And one overripe banana speeds up the rest.

Using Ethylene to Ripen Fruit Faster at Home

Apples, ripe avocados and yellow bananas give off most gas at roughly room temperature, about 59 to 77°F.21Mess Brands. Ethylene Producing Fruits and Vegetables: Chart & Storage Guide Cold avocados make very little ethylene.22Mess Brands. Ethylene Producing Fruits and Vegetables: Chart & Storage Guide So ripen fruit on the counter, then refrigerate it once ripe to slow things down.

Put the hard avocado, pear, peach or kiwi in a paper bag, and add a ripe banana or apple to boost the gas. Fold the top closed. Paper lets moisture out, unlike plastic. Check daily; avocados often soften in one to three days. The method speeds up ripening that was going to happen anyway; it can’t create ripening in fruit that can’t do it. Bagging strawberries, grapes or citrus won’t make them sweeter, and plastic bags trap moisture and invite mould.

Keep the bag on the counter away from direct sun; room warmth helps gas production, but too much heat doesn’t. A fridge shelf defeats the purpose because output drops sharply there. Avoid putting it right beside a window or stove, where it could overheat.

To tell when fruit is ready, an avocado yields to gentle pressure near the stem. Pears soften at the neck first. Peaches smell fragrant and give slightly.

Bruises and Cuts Make Fruit Give Off More Gas

Bruising or other physical injury can make fruit produce extra ethylene.23PubMed Central. Mechanical Injury Enhances Ethylene-Associated Transcriptional and Metabolic Responses of Strawberry Fruit During Shelf-Life Period In papaya, bruising caused a short surge of gas-making activity within a couple of days.24PubMed Central. Proteomic Analysis of Mechanical Injury Effects in Papaya Fruit at Two Maturity Stages A single damaged fruit can therefore speed ripening of those around it.

The fruit responds to injury by making extra gas around the damaged spot, which can start softening nearby areas of the same fruit, so bruises seem to spread. Even an unripe fruit can react to damage.

Set fruit down rather than dropping it into the bowl, and avoid stacking heavy fruit on soft fruit. Remove bruised or split pieces from bags and drawers, and use them first, in smoothies or baking.

How Stores Ripen and Preserve Fruit With Ethylene

Bananas and tomatoes are often picked unripe and ripened in special rooms filled with ethylene.25Postharvest Technology of Perishable Horticultural Commodities. Postharvest Technology of Perishable Horticultural Commodities The rooms control temperature, humidity and gas level so a batch ripens evenly.26PubMed Central. Induced Ripening Agents and Their Effect on Fruit Quality of Banana Fruit is picked firm because firm fruit survives shipping without bruising, and ripening is delayed until it’s near the store. Gas is added to the air for a set time to start ripening across the whole batch at once. Then it’s vented out and temperature is managed to control how fast the fruit continues. The gas is the same one fruit makes naturally, and it airs out of the fruit rather than being eaten as residue.

Oranges, grapefruit and mandarins are sometimes exposed to ethylene to turn green peel orange.27Postharvest Biology and Technology. Does ethylene degreening affect internal quality of citrus fruit? This changes the peel only; the sugar, acid, vitamin C and flavour of oranges and grapefruit stay the same.28Postharvest Biology and Technology. Does ethylene degreening affect internal quality of citrus fruit? Citrus can be ripe inside while the peel is still green, especially in warm climates where the peel keeps its chlorophyll.

Going the other way, some fruit is treated with 1-MCP, a ripening blocker that locks onto the fruit’s ethylene sensors.29Postharvest Biology and Technology. Effects of ethylene and 1-methylcyclopropene treatments on physiological changes and ripening-related gene expression of ‘Mopan’ persimmon fruit during storage The fruit stops responding to the gas and stays fresh longer in storage.30Food and Humanity. Mechanism, application and prospect of 1-methylcyclopropene on post-harvest fruit quality maintenance That’s why stored apples can still be crunchy many months after harvest. The effect is temporary, since fruit eventually makes new sensors and starts to respond again. Some packaging contains purple potassium permanganate, which breaks ethylene down and turns brown when used up.31PubMed Central. The Emergence and Impact of Ethylene Scavengers Techniques in Delaying the Ripening of Fruits and Vegetables

For shoppers, apples bought months after harvest may have been treated to stay crisp, and treated fruit may ripen slowly or unevenly on your counter. Absorber sachets for fridges work on the same principle and need replacing when spent.

How Ethylene Affects Flavour and Aroma

Cold storage can dull a kiwifruit’s fruity aroma compounds.32PubMed. The impact of cold storage and ethylene on volatile ester production and aroma perception in ‘Hort16A’ kiwifruit A day of ethylene before ripening restored a stronger tropical, candy-like aroma and less green smell.33PubMed. The impact of cold storage and ethylene on volatile ester production and aroma perception in ‘Hort16A’ kiwifruit Letting cold-stored kiwis ripen near an apple at room temperature may therefore improve flavour. Cold slows the machinery that builds aroma, so fruit can look ripe but taste flat.

For the best flavour, ripen gas-driven fruit on the counter first, then chill it; refrigerating unripe fruit can leave it bland. Fully ripe fruit’s aroma is one useful readiness signal among several.

Tomatoes are the clearest case. They lose much of their aroma when chilled, which is why a fridge tomato often tastes watery. Keep unripe ones on the counter so they finish ripening and build flavour. If a ripe tomato can’t be eaten soon, the fridge slows spoilage, and bringing it back to room temperature before eating recovers some of the aroma.