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 color, aroma, and flavor. 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.

by the United States Food and Drug Administration (FDA). Given the numerous amounts of food substances, the FDA does not categorize every one. Salt, pepper and vinegar are examples. These, along with ethylene, all are within the category of food substances that, when used for the purposes indicated, in accordance with good manufacturing practice, are regarded by the FDA as generally recognized as safe (GRAS) for such uses.

Calcium Carbide is used in some countries as source of acetylene gas, which is an artificial ripening agent. However, acetylene is not nearly as effective for ripening as is ethylene, and acetylene is not a natural plant hormone like ethylene. Also, calcium carbide may contain traces of arsenic and phosphorus, both highly toxic to humans, and so the use of this chemical for ripening is dangerous and illegal in most countries.

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.

At their minimum temperature levels, fruit is basically inactive and does not respond well to externally supplied ethylene.

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

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:

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 gasoline powered engines all produce ethylene in amounts large enough to cause damage to the ethylene-sensitive produce items mentioned
Ventilate the storage area, preferably to the outside of the warehouse, on a continuous or regular basis to purge the air of any ethylene
Remove ethylene with ethylene absorbing filters. These have been proven in reducing and maintaining low ethylene levels

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 1600 ft3 or larger (45 m3).

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

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.

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 color will not be uniform and the peel will be dull, pale yellow, and unattractive.

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.

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.

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.

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.

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

Ultrasonic humidifiers are the quietest humidifiers available, and the ideal choice when noise level is a concern (if you are a light sleeper). In general, a warm moisture humidifier will be much quieter than a cool moisture evaporative humidifier. Warm moisture models release steam vapor into the air without the use of loud, powerful fans; instead of a loud fan, you will hear a quieter boiling/gurgling noise caused by the heating of the water into steam. Cool moisture evaporative humidifiers use a fan to blow air through an evaporative wick filter, which makes more noise than a warm moisture humidifier. The amount of fan noise depends on the fan speed setting, so a humidifier with many fan speeds offers you more flexibility in choosing the best level of humidity output and noise level for your needs. In general, when running on the lowest fan speed, cool moisture evaporative humidifiers produce a quiet background “white noise”, which many people find helpful when sleeping.

Most evaporative cool moisture humidifiers use replaceable wick filters, and these should be changed every 1-2 months on average (wick filter life varies depending on your specific humidifier model, frequency of use, and your water’s mineral content). Most wick filters are coated with a special antimicrobial coating designed to slow the growth of mold on the filter. Warm moisture humidifiers do not use wick filters at all but will need to be cleaned regularly to remove hard water mineral buildup. Most ultrasonic humidifiers use optional demineralization cartridges, which help reduce mineral deposits found in tap water which can exit the humidifier in the form of white dust.

White dust is a byproduct of minerals found naturally in water, which can sometimes be released into the air during the humidification process. White dust, which can be a nuisance but is not harmful, may settle on surfaces and furniture near the humidifier. It is easily cleaned just as you would normally dust. Warm moisture (steam vaporizers) and evaporative cool moisture humidifiers do not release any white dust into the air. The only types of humidifiers that can potentially release white dust are ultrasonic humidifiers and cool mist impeller humidifiers. Many ultrasonic humidifiers come with an optional demineralization cartridge designed to trap minerals before they can become airborne, thus reducing white dust. You can also use ultrasonic humidifier water treatment to reduce white dust. The amount of white dust you may experience will vary depending on the mineral content of your water supply. If white dust is a concern, you can use distilled water in your humidifier instead of regular tap water. Distilled water has very low mineral content and will not produce white dust. For other types of humidifiers, using distilled water will also reduce the amount of time you will need to clean your humidifier, and will help prolong filter life.

Your humidifier should be cleaned regularly to prevent the growth of mold, mildew, fungi, and bacteria. These organisms can thrive in standing water that is left inside your humidifier for more than a couple of days. It is best to empty and refill your humidifier on a daily basis, or keep your humidifier running throughout the day, to avoid having standing water sitting in your humidifier. Regular cleaning is recommended at least once every 1-2 weeks. The product manual that comes with your humidifier will have specific instructions as to the best way to clean and maintain your humidifier. Please follow your specific humidifier’s cleaning instructions carefully to ensure the most healthy and efficient operation of your humidifier. Humidifier cleaning solution can help you clean and prepare your humidifier for efficient operation by removing lime scale buildup and sludge deposits.

Most humidifier manufacturers publish a recommended room size (in square feet) for each model they produce. A recommended room size is not a guarantee that the humidifier will be able to raise the relative humidity (RH) level of any particular room size to any specific RH level. Room size recommendations should be used only as rough guidelines when shopping for a humidifier, as these recommendations are subjective, are based on ideal environmental conditions, and can vary from manufacturer to manufacturer. Each manufacturer bases their recommended room sizes on the maximum amount of moisture the humidifier is capable of producing per day, assuming the humidifier is operating in perfect environmental conditions, with the humidifier constantly running on its maximum speed setting.

Once a humidifier adds moisture to a room, there are many factors at work to dry out the air again. These factors, which vary from room to room, day to day, even hour to hour, include: Outdoor and indoor temperatures, indoor heating level and type of heat (forced air, baseboard, wood stove, etc), location of air ducts, location and insulation of windows/doors, ceiling height, how well the room is closed off and sealed, etc. The maximum RH level possible in your room depends on your unique room environment.

We choose to publish manufacturer’s recommended room sizes because that is how most humidifiers are sold today. However, after years of our own testing of every humidifier we sell in real world conditions, we have found that you will get the best performance by using the highest output humidifier possible that will fit in your room and budget.

Often confused with humidifier capacity, humidifier output refers to the maximum gallons of water the humidifier is capable of producing per day, and is the best way to compare the effectiveness of various humidifiers. Humidifiers can vary in output anywhere from 1 to 14 gallons per day (for example, a humidifier with an output of 10 gallons per day will be capable of producing 5 X more moisture than a humidifier with a 2 gallon output). Regardless of a humidifier manufacturer’s recommended room size, two humidifier models that each have an output of 4 gallons per day will be equally effective. While recommended room sizes can give you a general idea of which humidifiers to consider, a more useful and accurate piece of information is the humidifier output, which allows you to more easily compare different humidifiers and their relative effectiveness.

Humidifier capacity is the maximum amount of water the humidifier can hold at any one time, and varies from 0.5 to 6 gallons, depending on the size of the humidifier. Output is the maximum amount of water the humidifier can add into the environment per day, and nearly all humidifiers have a higher output than capacity. The frequency with which you will need to refill your humidifier depends on your humidifier’s tank capacity relative to output, and the speed setting you select. If your humidifier has a 5 gallon output per day, and it has a holding capacity of 2.5 gallons, you will need to refill the humidifier every 12 hours in order to obtain the full possible 5 gallon maximum output per 24 hour period. The higher the tank capacity relative to the output, the less often you will need to refill the humidifier. In addition, you can go longer between refills if you run your humidifier on a lower speed, or if you do not run it constantly 24 hours per day.

Most humidifiers have a removable water tank which is filled at a sink or bathtub and then placed onto the humidifier base. As the water in the base of the humidifier is used, more water from the tank will be released into the base. Some humidifiers have an automatic shut-off feature which will turn the humidifier off once the water needs to be refilled. There are also some humidifiers with a “top-fill” (or front-fill) design, which eliminates the need for the removable water tank. With these humidifiers, you pour water directly into the top of the humidifier using a pitcher, cup, or any other water container. This can be helpful for those with arthritis or who may have trouble lifting and carrying a water tank.