Ethylene (C2H4) Fact Sheet and FAQs

We may be partial, but we think fruit ripening is the noblest of all ethylene’s uses. We hope you find our ethylene fact sheet helpful and informative.


Ethylene is an important, natural plant hormone.
It regulates the ripening and senescence (aging) of plants. Ethylene is normally produced in small quantities by most fruits and vegetables. However, climacteric fruits, like bananas, avocados and tomatoes create larger amounts of ethylene and this release of ethylene starts several actions like increased respiration, more ethylene production, and changes in colour, aroma, and flavour. Fortunately, the onset of this internal ethylene production can be controlled. The ability of fresh produce companies and distribution centers to apply ethylene allows the promotion of predicable ripening times and more uniform ripening…the result is better quality and consumer eating experience.

Ethylene has been found not harmful or toxic to humans in the concentrations found in ripening rooms (100-150 ppm).
In fact, ethylene was used medically as a anesthetic in concentrations significantly greater than that found in a ripening room. However, ethylene is often targeted as the reason for difficulty in breathing in ripening rooms; what can affect some people is usually either:

  • Carbon Dioxide (CO2,) levels: CO2, is produced by the ripening fruit in the room and levels increase over time, or
  • Oxygen levels: The oxygen in the room when loaded is taken in by the ripening fruit. This sometimes will make breathing in a ripening room difficult.

The increased CO2 and decreased oxygen levels are the main reasons for venting the ripening room.

Ethylene action slows at lower temperatures.
At their minimum temperature levels, fruit is basically inactive and does not respond well to externally supplied ethylene.

Ethylene will penetrate most substances.
In fact, it will permeate through produce cardboard shipping boxes, wood and even concrete walls.

Ethylene is harmful to many fruits, vegetables, and floral items.
While ethylene is invaluable due to its ability to initiate the ripening process in several fruits, it can also be very harmful to many fruits, vegetables, flowers, and plants by accelerating the aging 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. If ethylene damage is suspected, testing for ethylene levels should be performed (here are some ways to test). This will indicate if one of the steps below should be followed:

  1. Ethylene producing items (such as apples, avocados, bananas, melons, peaches, pears, and tomatoes) should be stored separately from ethylene-sensitive ones (broccoli, cabbage, cauliflower, leafy greens, lettuce, etc.). Also, ethylene is emitted by engines. Propane, diesel, and petrol powered engines all produce ethylene in amounts large enough to cause damage to the ethylene-sensitive produce items mentioned
  2. Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene
  3. Remove ethylene with ethylene absorbing filters. These have been proven in reducing and maintaining low ethylene levels

Ethylene is explosive at high concentrations.
At 27,000 ppm, just a spark can ignite ethylene and cause a deadly explosion. We have an entire section of our web site devoted to the explosions that can result from excessive ethylene: ethylene explosions. However, when using our products as directed, reaching the explosive level is not possible. The explosive level is about 200 times greater than the level necessary to initiate ripening. Always use our generators in ripening rooms that are 45 cubic meters or larger..

Ethylene is used to ‘degreen’ citrus.
This is a natural process that triggers pigment changes: the loss of green peel colour by removing the chlorophyll, which allows the orange or yellow to fully cover the entire peel. No loss of flavour is caused; this is merely a continuation of the natural plant process.


I hear that ethylene is explosive. How can I be sure that I’m safe from this danger?
Yes, ethylene is very explosive. At concentrations above 27,000 part per million (ppm), just a spark can cause it to explode. There have been several instances of explosions in ripening rooms where cylinders were in use…we have compiled a list of ethylene explosions.

However, the ripening process of most fruits can be initiated by ethylene at concentrations as low as 50 ppm, or less than 1% of the explosive level, and most operators ripen with 1,000 ppm or less. Catalytic Generators are the safest commercial form of ripening; they produce small, controlled amounts of ethylene and when used as directed, they cannot produce explosive amounts of ethylene. That is why so many fresh produce companies use our generators rather than gas cylinders.

When using our generator and Ethy-Gen® II Ripening Concentrate in rooms that are 1,600 ft3 (45 m3) or larger, there is NO CHANCE OF ETHYLENE EXPLOSION. The United Kingdom takes the threat of explosion from cylinders very seriously. The UK’s Health and Safety Executive/Local Authorities Enforcement Liaison Committee (HELA) has posted a circular on their web site explaining that generators are the preferred options for ethylene application and that the “use of cylinders of pure ethylene should be vigorously discouraged.” For more details, please click here.

Is ethylene really necessary for banana ripening?  Won’t they ripen on their own?
Bananas are harvested mature but very green in order to survive the trip from the growing regions to destinations across the world.  Along with a rise in pulp temperature, an external ethylene application will trigger the proper ripening process to begin, which includes the fruit producing internal ethylene. This natural process results in uniform, controlled and predictable ripening.  Without this exposure to external ethylene, bananas will eventually soften, but the change in colour will not be uniform and the peel will be dull, pale yellow, and unattractive.

I’m a student…how can I do an experiment with ethylene for ripening?  Do you sell your products to end users?
Please see this page for more information: Ethylene / Ripening Experiment


The following are common questions about the use of ethylene gas in the ripening process. The material is reprinted from a fact sheet1 that has been available to the industry for many years.

What is the effect of ethylene on fruit ripening?
Ethylene can promote ripening in tomatoes, bananas, citrus, pineapples, dates, persimmons, pears, apples, melons, mangos, avocados, papayas and jujubes – a clear indication that the action of ethylene is general and widespread amongst a number of fruits. It is clear that ethylene is a ripening hormone – a chemical substance produced by fruits with the specific biological phenomenon of accelerating the normal process of fruit maturation and senescence.

What do you mean ‘promote’ the ripening process?
Using tomatoes as an example, the life of a tomato fruit begins with fertilization of the flower ovules. After fertilization, the young fruit goes through a short period of cell division which is then followed by a rapid period of growth as these cells enlarge. During the final stages of growth and development, the tomato fruit reaches its full size and is now mature. This period of growth and development, from fertilization to development of the mature fruit, requires about 45-55 days, depending on the cultivar and the season. During the growth and development period, there are many chemical and physical changes occurring that have an impact on fruit quality and ripening behavior after harvest. Ripening is the final stage of the maturation process when the fruit changes color, and develops the flavor, texture and aroma that makes up what we define as optimum eating quality. The biological agent that initiates this ripening process after the fruit is mature is naturally produced ethylene – this simple plant hormone described and understood over 40 years ago. While there are other factors involved in this “triggering” of the ripening process by ethylene, it is essentially a universal ripening hormone. When this internal concentration of naturally produced ethylene increases to about 0.1 – 1.0 ppm, the ripening process is irreversibly initiated. The process may be slowed, but it cannot be reversed once it is truly under way. So, here is the key point: additional and externally applied ethylene, provided prior to the time that the naturally produced internal concentration reaches the required 0.1 – 1.0 ppm level, will trigger or initiate – “promote” if you will – this natural ripening process at an earlier time.

Doesn’t this still amount to an ‘artificial’ process?
No! The additional externally applied ethylene (the “gassing” so frequently referred to in the popular press) merely accelerates the normal ripening process. Numerous studies have shown that there are no important biochemical, chemical, or physiological differences between fruit ripened where the naturally produced ethylene has been the triggering mechanism or where additionally externally applied ethylene has triggered the process in the mature but unripe fruit.

Nevertheless, doesn’t the use of ethylene still allow the trade to ‘cheat’ the consumer with an inferior product?
For example, tomato fruit are not and cannot be “artificially reddened” by ethylene. The normal tomato ripening process, which includes pigment changes – the loss of green chlorophyll and conversion of carotenoids into red lycopene pigments – can be accelerated and brought about earlier by externally applied ethylene, but this is a normal process. In fact, some of the components of nutritional quality, such as Vitamin C content, benefit because of the fact that the fruits will be consumed after a shorter time interval from harvest as a result of ethylene treatments and hence, the initial level will not have degraded as far as the longer, un-accelerated process.

What are the factors that result in the poor quality tomatoes we often see on the market?
Although many factors could be listed, there are four which play the dominant role in determining the quality of tomato fruits presented to the customer in the retail store:

  1. Variety
  2. Maturity at time of harvest
  3. Storage temperature during shipping and handling (this is probably the most common cause; tomatoes are often shipped or stored at improper temperatures, which causes severe taste loss…never allow tomato pulp temperature to go below 55°F!)
  4. Physical damage

1 – Source: California Fresh Market Advisory Board, Informational Bulletin No. 12, June 1, 1976.