Ethylene gas is an odourless, colourless gas that exists in nature and which is triggered at maturity in climacteric fruits. Ethylene, also known as either the ‘death or ripening hormone’, plays a regulatory role in many processes of fruit & vegetable growth, development, and eventually decay.

Fruits are either ethylene producers or absorbers. Apples, bananas, melons, pears, and peaches are ethylene producers. Tomatoes are moderate ethylene producers. Broccoli, cabbage, cauliflower, etc., are ethylene sensitive.

So, by this rule of thumb, it is preferable to avoid storing ethylene producing fruits with ethylene absorbing ones. Ventilating the storage area also serves the purpose but just to an extent.

Apples are ethylene producers while cauliflower is ethylene sensitive. Here we have a general list of climacteric and non-climacteric fruits and vegetables to help you gain a better understanding of what categories these fruits and vegetables are defined by;

Ethylene Producing Fruits & VegetablesFruits & VegetablesEthylene EmissionEthylene SensitivityApplesHighYesApricotsHighYesAvocados (ripe)HighYesAvocados (unripe)LowYes, VeryAvocados (unripe)LowYes, VeryBananas (green)LowYesBananas (ripe)MediumNoBlackberriesVery LowNoBlueberriesVery LowNoCantaloupeMediumYesCherriesVery LowNoCucumbersVery LowYesEndiveNoNoFigsLowNoGrapefruitVery LowNoGrapesVery LowYesGuavasMediumYesKiwi (ripe)HighYesKiwi (unripe)LowYes, VeryLemonsVery LowNoLimesVery LowNoLycheesVery LowNoMangoesMediumYesMelons, Honey DewMediumYesNectarinesHighNoOkraVery LowYesOrangesVery LowNoPapayasMediumYesPeachesHighYesPearsHighYesPineapplesVery LowNoPlumsHighYesPrunesHighYesQuincesHighYesRaspberriesVery LowNoStrawberriesVery LowNoTangerinesVery LowNoTomatoes (green)LowYesTomatoes (ripe)MediumNoNO Ethylene Emission, Not SensitiveFruits & VegetablesEthylene EmissionEthylene SensitivityArtichoke SweetNoNoCherriesNoNoChicoryNoNoCoconutsNoNoCornNoNoCranberriesNoNoGarlicNoNoGingerNoNoKohlrabiNoNoOnionsNoNoPeppers sweetNoNoPomegranatesNoNoRhubarbNoNoEthylene Sensitive Fruits and VegetablesFruits & VegetablesEthylene EmissionEthylene SensitivityAsparagusNoYesAvocados (ripe)HighYesAvocados (unripe)LowYes, VeryBananas (green)LowYesBasilNoYesBeetsNoYesBok ChoyNoYesBrussels SproutsNoYesCabbageNoYesCantaloupeMediumYesCarrotsNoYesCauliflowerNoYesCeleryNoYesCucumbersVery LowYesEggplantNoYesGrapesVery LowYesGreen BeansNoYesGreen PeasNoYesGuavasMediumYesHerbsNoYesKiwi, ripeHighYesKiwi (unripe)LowYes, VeryLeeksNoYesLettuceNoYesMangoesMediumYesHoney DewMediumYesMushroomsNoYesOkraVery LowYesPapayasMediumYesParsnipsNoYesPeachesHighYesPearsHighYesPeppers (hot)NoYesPersimmonsNoYes, VeryPlumsHighYesPrunesHighYesPotatoesNoYesPumpkinsNoYesQuincesHighYesRadishesNoYesRutabagasNoYesSalad MixesNoYesSproutsNoYesSquashes (summer)NoYesSquashes (winter)NoYesSweet PotatoesNoYesTomatoes (green)LowYesTurnipsNoYesWatermelonNoYes

Commercial use of ethylene to ripen fruit

The overall effect of Ethylene is to hasten ripening, ageing and eventually spoilage. Some examples of bad effects of ethylene on some common fruits and vegetables are; scald, brown spots, decay, sprouting, mould, odour, yellowing, bitterness, and loss of colour.

Presence of ethylene in amounts ranging from a few parts per billion (ppb) to a few parts per million (ppm) can reduce the vigour of fresh produce stock, decrease product life expectancy and reduce overall stock quality.

Climacteric fruits are frequently harvested at a physiological stage that is considered ‘commercial maturity’, typically in a hard green but mature stage just before ripening has initiated. Examples include bananas, mangoes, tomatoes and avocados. This enables the fruit to be harvested, cooled, stored and transported significant distances to where it will be marketed and consumed.

Ripening can then be conducted under controlled conditions of temperature, relative humidity and ethylene to achieve uniform appearance and quality of ripe fruit. Fruit is placed into specially constructed ripening rooms and brought to optimum ripening temperature and humidity. Ethylene is then raised to a prescribed concentration using either a "catalytic generator" that makes ethylene gas from liquid ethanol or from commercially available gas supplies. Forced-air cooling systems ensure that fruit is uniformly exposed to the room ethylene concentration. When fruit is exposed to ethylene under these controlled conditions they will initiate their respiratory climacteric pattern and ripen at a relatively uniform rate. Conditions and duration can be varied to suit customer specifications for stages of ripening and colour development.

Treatment times vary depending on conditioning and ripening stage required but once fruit has reached the desired pulp temperature a treatment time of 24 hours with a room ethylene concentration of 10 microlitres to the litre (10 µL/L) is sufficient to stimulate coordinated ripening for many climacteric fruits.

As fruit respiration rates increase in response to ethylene treatment it is important to ventilate rooms to prevent the build-up of carbon dioxide, emitted as a respiration by-product.

‘Ripe ‘n’ ready’

‘Ripe ‘n’ Ready’ is a retail strategy used for marketing climacteric fruits to consumers in a ready-to-eat state. Consumers are increasingly purchasing less quantity per shopping event but shopping more often. Traditionally consumers would need to plan ahead when purchasing climacteric fruit in the early stages of ripening and wait for the fruit to ripen before consuming.

The Ripe ‘n’ Ready strategy is to pre-condition/ripen climacteric fruit to be able to present consumers with a ready-to-eat product. To achieve this requires a synchronised supply chain that can ensure timely delivery of fruit after the ripening treatment has been applied.

‘Vine-Ripe’

Some new varieties of tomatoes are marketed as ‘vine-ripened’. These ‘truss tomatoes’ develop their colour and flavour while still attached to the plant. They have been developed through crossbreeding with non-ripening tomato varieties and are usually grown hydroponically in greenhouses. They develop colour without softening like conventional tomatoes and remain firm for harvest, packing and distribution. These tomato varieties do not exhibit a climacteric like conventional tomato varieties but remain susceptible to external ethylene.