What is Ethylene?

Ethylene title image

We’ve all at one point or another heard the idiom “One bad apple, ruins the bunch”, but not everyone knows that this particular saying is directly related to the effect that one overripe apple can have on the other apples, as it continues to emit ethylene into the surrounding atmosphere, accelerating the ripening and senescence of the entire bunch in the process.

So, what exactly is Ethylene and how is it being utilised to maximise the outgoings of fruits & vegetables across global supply chains?

What is Ethylene?

Ethylene is the most commercially produced organic compound in the world and is used in many industrial applications.

Colourless and flammable, Ethylene (C2H4) is a small hydrocarbon natural gas and a naturally occurring hormone produced by plant cells that aids in the ripening and ageing process of fresh produce. Fruits such as apples and pears emit a greater amount of ethylene gas, which as a result affects their ripening process. Other fruits, like cherries or blueberries, have very little ethylene production, therefore, it does not greatly impact the ripening process.

Due to ethylene biosynthesis being so important for the ripening of some fruits and vegetables, it is sometimes used by commercial agribusinesses to speed up the ripening process of crops.

What are its effects on Fruits and Vegetables?

While ethylene is invaluable due to its ability to initiate the ripening process in several fruits and vegetables, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the ageing process and decreasing the product quality and shelf life. The degree of damage depends upon the concentration of ethylene, length of exposure time, and product temperature.

Fruits and vegetables play a vital role in human nutrition. One of the few factors that influence their economic value is the relatively short ripening period and reduced postharvest life they often have. Over-ripening of fruits and vegetables leads to excessive softening which results in spoilage and damage during shipping and handling. 

Slowing the process of ripening and quality decline extends the storage and shelf life of fresh fruits and vegetables. Monitoring the shelf life of fresh produce not only helps the grower to save on postharvest losses but consumers also benefit in terms of retained fresh­ness over longer periods, resulting in value addition to the fruits and vegetables.

Understanding the fundamental relationship between ethylene and fruit respiration rates during ripening is necessary in order to manage the harvesting, storage and distribution processes. 

When the chemical is exposed to fresh produce, it latches on to their ethylene receptors and stimulates the maturing stages of the produce. The chemical reaction within fruits and vegetables then brings forth the development of flavours, vitamins, firmness, aroma, texture, and colour in the produce. However, too much Ethylene exposure before shipments meet their required timelines and destinations, can lead to overripeness, a decline in product quality and an increase in Volatile Organic Compounds (VOCs) throughout the stock.

One of the biggest contributors to mass amounts of waste within the fresh produce sector is directly linked to cases of overexposure to ethylene during the ripening and storage process. On a global scale, the main contributor to food waste is fruits and vegetables with an astounding 45-50% of all harvested fresh produce being lost or wasted within the food supply chain. This is roughly 1.3 billion tonnes of food, which equates to $680 Billion US Dollars of wasted fresh produce each year.

The effects of ethylene on vegetables can be avoided or reduced by:

  •           Low-temperature storage. Below 5°C, the effects of ethylene are greatly reduced.
  •           Keeping the storage area ventilated to avoid the build-up of ethylene inside.
  •           Removing ethylene from storage rooms by reacting it with potassium permanganate (KMnO3).
  •           Oxidising ethylene by reacting it with ozone (O3). 
  •           Storage in an atmosphere with high CO2.
  •           Air scrubber systems for storage cleansing.

Conventional Practices are Harmful to Fruits and Vegetables

Any closed environment, such as truck trailers, shipping containers, warehouses and cold rooms, will have a similar effect resulting in increased concentration of Ethylene.

At the latter part of post-harvest, artificial ripening by using ethylene gas is a general practice as it ensures that the product reaches the retail outlets with a degree of ripeness, which brings out its best in terms of taste, colour, texture and nutritional value. One of the most common examples is the ‘forced’ ripening of bananas during high demand periods.

However, these conventional methods adopted by most warehouses and cold stores of lowering the temperature and humidity and using gases like nitrogen and sulphur increase the shelf life but have several drawbacks.

  •           It uses toxic gases
  •           It is dangerous for human health
  •           It changes the natural properties of fruit as well

Refrigeration and humidity control slow decay but are not enough to halt the production of ethylene gas in cold stores and warehouses. Even a small amount of ethylene gas during storage is enough to hasten the process of decay of fresh produce. This makes ethylene control absolutely necessary in the cold chain.

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, while tomatoes are moderate ethylene producers. Broccoli, cabbage, and cauliflower are just a few examples of ethylene sensitive absorbers.

So, by the 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.

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 the stage of ripening and colour development.

Treatment times vary depending on conditioning and ripening stage required but once the fruit has reached the desired pulp temperature a treatment time of 24 hours with a room ethylene concentration of 10 micro-litres 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’. 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.

Final Thoughts

Monitoring and controlling ripeness of fresh produce are becoming very important issues in the fruit industry since the state of ripeness during harvest, storage and market distribution determines the quality of the final product measured in terms of customer satisfaction. 

Many methods to monitor the ripeness of fruits and vegetables have already been proposed. The main disadvantage of the majority of these techniques is that they are not practical for cultivars or storage stations. Moreover, most of them require the destruction of the samples used for analysis. 

This is why, nowadays, optimal harvest dates and predictions of storage life are mainly based on practical experience. Leaving these critical decisions to subjective interpretation implies that large quantities of fruit are harvested too soon or too late and reach consumer markets in poor condition.

How PostHarvest helps optimise Ethylene levels across supply chains

PostHarvest has developed a form of amplification technology, which allows users to accurately measure and forecast optimal delivery times, maximise outgoings and minimise food wastage. PostHarvest’s amplification technology allows for atmospheric reads in the form of parts per billion (PPB), this measurement is often used to describe concentrations of contaminants found within an atmosphere in its most precise and finite form (currently an unmatched industry standard).

PostHarvest’s Environmental Sensor is a wall-mounted device that sits within storage facilities as it continuously captures ethylene samples, along with other chemical compounds from within the controlled atmosphere of a cold chain operation, providing the most accurate ripeness readings in the industry. This data provides conditioning & health reports to help cool store operators forecast their processes, supplies and optimal delivery times, maximising outgoings and minimising food wastage as a result.

Head of Content for PostHarvest

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