Artificial Ripening of Fruits: Methods and Biological Effects of Ethylene

Every ripe banana on a supermarket shelf, every tomato with its deep red colour, and every mango with its sweet tropical aroma has gone through one of the most precisely managed processes in modern agriculture – controlled ripening. Fruits do not simply ripen by chance after harvest. The process is governed by a gaseous plant hormone called ethylene, and understanding how to harness it is central to post-harvest management. This post covers how fruits are classified by ripening behaviour, what ethylene does inside the fruit at a biological level, and how the fruit industry applies it artificially through carefully controlled systems.

How fruits are classified: climacteric vs. non-climacteric 🔗

Not all fruits ripen the same way, and this distinction has a direct bearing on how they are handled after harvest. According to the University of Maryland Extension, climacteric fruits can ripen after they are picked, while non-climacteric fruits cannot ripen after harvest and must be picked when fully mature.

Research published in PMC describes two distinct patterns clearly: in climacteric fruits, as ripening proceeds there is a sharp respiratory peak accompanied by a high level of ethylene production. In non-climacteric fruits, the respiration rate is almost constant or shows a steady decline until senescence, with little or no increase in ethylene production. This difference makes climacteric fruits far more suitable for artificial ripening techniques.

Common climacteric fruits include bananas, mangoes, tomatoes, apples, avocados, papayas, apricots, peaches, and pears. Non-climacteric fruits include cherries, grapes, strawberries, citrus fruits, and pineapples. Felix Instruments’ post-harvest resource notes that non-climacteric fruits do not respond meaningfully to ethylene applications and therefore ripening rooms are designed specifically for climacteric varieties.

The autocatalytic nature of ethylene in climacteric fruits 🔗

One of the most important features of ethylene production in climacteric fruits is that it is autocatalytic. Frontline Services explains this well: an initial small concentration of ethylene causes the fruit to produce greater quantities of ethylene, until a peak concentration is achieved. Once triggered, the process cannot be stopped – it continues to accelerate ripening. This is why exposing immature climacteric fruit to ethylene prematurely can trigger poor-quality ripening, and why even small quantities of the gas must be carefully managed in storage.

PMC research on banana ripening further distinguishes two biosynthesis systems. System 1 produces very low levels of ethylene during the pre-climacteric stage and in non-climacteric fruits throughout ripening. System 2, which is exclusive to climacteric fruits, is autostimulated and responsible for the large surge in ethylene that drives ripening to completion.

Biological effects of ethylene on fruit ripening 🔗

Ethylene is a colourless, flammable gas with the chemical formula C₂H₄. A comprehensive review published in PMC on ethylene and its role in fruit ripening describes ripening as a coordinated sequence of physiological changes that unfold in stages. These changes are what transform a hard, starchy, unpalatable fruit into a soft, sweet, aromatic, and nutritious product.

Colour change 🔗

The most immediately visible effect of ethylene is colour change. University of Maryland Extension notes that the green background colour fades as ethylene promotes the degradation of chlorophyll, the green pigment present in unripe fruit. Wikipedia’s entry on ripening clarifies that colour change is not simply the result of pigment destruction – additional pigments are actively synthesised as the fruit ripens. In tomatoes, the red pigment lycopene is produced; in bananas, yellow carotenoids and xanthophylls emerge from beneath the green surface. Ethylene is also used commercially to de-green citrus fruits, triggering chlorophyll breakdown to produce the familiar orange and yellow peel colour without affecting flavour.

Softening 🔗

Research published in Food Quality and Safety (Oxford Academic) identifies textural change as one of the major characteristic features of fruit ripening. Ethylene activates a battery of cell wall-modifying enzymes – including polygalacturonase, pectin methylesterase, cellulase, and expansins – that break down pectin and structural polysaccharides in the cell walls, causing the fruit flesh to soften progressively. Wikipedia explains that pectin, which forms part of the cell wall, is converted from a water-insoluble form to a soluble one by these degrading enzymes, directly reducing the fruit’s firmness.

Sugar accumulation and sweetness 🔗

Frontiers for Young Minds describes this clearly: during ripening, starch inside the fruit breaks down and simple sugars – sucrose, glucose, and fructose – increase, making the fruit taste sweet. The effect is especially pronounced in bananas, which contain almost no sweet taste when green. The Oxford Academic review also highlights that in bananas, part of the texture change is specifically due to the conversion of insoluble starch to soluble sugars. Alongside sweetness, organic acid levels decrease during ripening, further improving palatability.

Aroma development 🔗

The PMC review explains the sequence of changes well: during the mid-ripening stage, breakdown of cell wall components leads to fruit softening while aroma volatile compounds begin to be synthesised. Later, cell wall degradation reaches its peak and the characteristic aroma fully develops, alongside complete conversion of starches to sugars. These volatile organic compounds are responsible for the fruit-specific scents associated with ripe mangoes, bananas, and strawberries. QA Supplies notes that at the peak of the ripening process, fruits produce these composites – and when the fruit is overripe, cell walls completely disintegrate, the skin darkens, and the fruit becomes unmarketable.

Artificial ripening: applying ethylene commercially 🔗

Because climacteric fruits can be harvested while still green and physiologically mature, the fruit industry routinely picks them before natural ripening begins. This extends transport life and reduces physical damage during shipping. Frontline Services explains that climacteric fruits are frequently harvested at a stage considered “commercial maturity” – in a hard, green but mature state just before ripening initiates. Ripening is then conducted under controlled conditions of temperature, relative humidity, and ethylene in specially designed ripening rooms.

According to Frontline Services, fruit placed in these rooms is brought to the optimum ripening temperature and humidity, and ethylene is raised to a prescribed concentration using either a catalytic generator that makes ethylene from liquid ethanol, or from commercially available gas supplies. The gas mixture used commercially is typically about 4% ethylene in nitrogen – a ratio that ensures effectiveness while keeping the mixture non-flammable.

The shot system 🔗

The shot system involves the periodic, intermittent introduction of concentrated ethylene gas into a sealed ripening chamber. Felix Instruments specifies that shot injection administers gas periodically every six to eight hours to reach the required level, up to 100 ppm. This system is best suited to fruits that require quick and uniform ripening – such as bananas and tomatoes – and rooms using this approach must be manually ventilated by opening doors at each injection cycle to allow CO₂ to escape. The method is fast and effective but demands careful monitoring to avoid over-ripening or uneven gas distribution.

The trickle system 🔗

The trickle system – also referred to as the flow-through system – involves a continuous, low-concentration supply of ethylene into the ripening chamber. Felix Instruments notes that trickle injection supplies ethylene constantly and its ventilation system continuously releases inside air while drawing in fresh air. This creates a more gradual and controlled ripening environment. The trickle system is particularly suited to fruits that benefit from a longer ripening period, such as avocados and kiwis, and it carries a lower risk of over-ripening or localised ethylene build-up.

Both systems can also use catalytic generation, in which ethylene generators produce the gas from ethanol concentrate inside the ripening room at scheduled intervals. Catalytic Generators LLC highlights that ethylene generators with catalytic concentrates can safely produce the gas needed for ripening, and the steady production of these generators means continuous monitoring is not always required.

Managing the ripening environment: temperature, humidity, and CO₂ 🔗

Ethylene alone does not determine ripening quality. The conditions inside the ripening room must be precisely controlled across multiple parameters to ensure the process runs uniformly and produces commercially acceptable fruit.

Temperature 🔗

Felix Instruments states that ripening occurs faster at higher temperatures and slows at low temperatures. Evikon MCI recommends that the air temperature in ripening rooms is typically raised to 20°C but not above 25°C to accelerate the process. For bananas specifically, Catalytic Generators LLC recommends an initial ethylene application of 100-150 ppm for a minimum of 24 hours during the first phase of ripening, with the full process taking 4 to 8 days depending on the target ripeness stage. Different fruits have different optimal pulp temperature ranges, and these are followed via ripening stage guides rather than room temperature readings alone.

Relative humidity 🔗

Humidity control is equally critical. Evikon MCI explains that ethylene treatment can dehydrate fruits, causing cracks and spotting that reduce marketable quality. Maintaining relative humidity between 85% and 100% makes the ripening process gradual and significantly improves product quality. Growing Produce confirms that at warm ripening temperatures, water loss from fruit can be very high if 85-95% relative humidity is not maintained, making proper humidification a core operational requirement.

CO₂ and ventilation 🔗

As fruits respire during ripening, they release CO₂ as a by-product. Evikon MCI states that CO₂ concentrations in excess of 1% (10,000 ppm) already slow down the ripening process and can affect product quality. Growing Produce recommends that ripening rooms be ventilated at minimum once every 24 hours, and that fruits with high respiration rates – like bananas and avocados – may require about two air exchanges per hour in a room filled with fruit. Ventilation must be directed to the outside and not into adjacent cold storage areas, as ethylene from ripening rooms can trigger premature senescence in green vegetables or stored non-climacteric fruits.

Extending green life and market planning 🔗

The ability to artificially control ripening gives producers and distributors a significant commercial advantage. By harvesting climacteric fruits at physiological maturity and keeping them in green life through low-temperature storage with suppressed ethylene, operators can time ripening to coincide with demand. Postharvest Technologies explains that ripening rooms are used in accordance with the general practice of picking fruits when still green, so there is ample time between harvesting and distribution. The green produce is then ripened – either naturally or with assisted ethylene – as it approaches the point of sale.

Conversely, where the goal is to extend storage life rather than trigger ripening, ethylene must be actively removed. The University of Massachusetts Extension notes that commercial products such as potassium permanganate pellets can absorb ethylene from storage environments, and ventilation further reduces ambient concentrations. A review published in MDPI Horticulturae describes a wider range of tools – ethylene inhibitors, adsorbents, and scavengers by catalytic oxidation – that are used to block or eliminate ethylene’s effect and extend postharvest life of climacteric fruits. Among the most commercially significant is 1-MCP (1-methylcyclopropene), a synthetic compound that blocks ethylene receptors in the fruit, delaying ripening, maintaining firmness, and extending storage life without altering the fruit’s eventual ripening quality.

Together, these ripening and storage tools allow producers to plan fruit releases across weeks and months rather than days, reducing waste, improving shelf presence, and enabling year-round availability of seasonal fruits in distant markets.

What do you think? Given that climacteric fruits like bananas and mangoes are harvested green and ripened thousands of kilometres from their origin, how dependent is the global fruit supply chain on ethylene management – and what would happen if that technology were suddenly unavailable? And as 1-MCP and other ethylene-blocking technologies become more widespread, should there be tighter international guidelines governing their use and disclosure to consumers?

References

1. https://extension.umd.edu/resource/ethylene-and-regulation-fruit-ripening
2. https://pmc.ncbi.nlm.nih.gov/articles/PMC6521425/
3. https://felixinstruments.com/blog/the-ripening-room-resource/
4. https://www.frontlineservices.com.au/Frontline_Services/Fruit_ripening_gas_-_ethylene.html
5. https://pmc.ncbi.nlm.nih.gov/articles/PMC11579711/
6. https://en.wikipedia.org/wiki/Ripening
7. https://academic.oup.com/fqs/article/1/4/253/4735143
8. https://kids.frontiersin.org/articles/10.3389/frym.2018.00016
9. https://qasupplies.com/blog/ethylene-fruit-ripening/
10. https://www.catalyticgenerators.com/blog/a-smarter-approach-to-monitoring-amp-management-of-fruit-storage-and-ripening-facilities
11. https://evikon.eu/news/what-should-be-measured-in-ripening-rooms-a-5/
12. https://www.catalyticgenerators.com/banana-ripening
13. https://www.growingproduce.com/fruits/tips-to-help-you-manage-postharvest-ripening/
14. https://www.postharvest.com/what-is-ethylene/ripening-of-climacteric-non-climacteric-fresh-produce
15. https://nevegetable.org/cultural-practices/postharvest-handling-and-storage
16. https://www.mdpi.com/2311-7524/10/8/840