Ethylene Gas

Why has someone wrapped the stems of our bananas? It’s all about the gas!

Wrapped bananas (Kate Russell)

​Bananas and many other fruits give off a gas as they ripen. This gas is called ethylene. Ethylene gas is also given off as a reaction to injury. 


​Often called the ‘ripening hormone’, ethylene gas is far more than that. It is a naturally occurring gas that regulates growth, development, and death of many different plants. When a plant is injured, ethylene gas redirects the plant’s biological activities to help it heal more quickly. Ethylene is what causes plants to die naturally. It also why your bananas turn brown when stored near apples.


Effects of ethylene gas

Ethylene is a small hydrocarbon molecule that stimulates the changes in texture, hardness, and color that we associate with ripening. Ethylene gas stimulates many other effects:

• abscission - leaf and ripe fruit drop
• adventitious root development
• bud damage 
• chlorophyll destruction and yellowing
• epinasty - stem bending
• flower drop
• flowering of bromeliads, such as pineapple
• inhibits auxin transport
• inhibits flower development
• inhibits stem and root elongation
• respiration
• seed germination
• senescence - deterioration related to aging
• vegetable yellowing

Ethylene gas is used in commercial agriculture to ripen fruit at a specific rate, so that they can pick and ship (flavorless) green fruit and then ripen it artificially. Anti-ethylene products are also used in agriculture:

• silver thiosulfate is sprayed on flowers to slow petal drop
• aminoethoxyvinylglycine is sprayed on fruits and vegetables to slow ripening during shipping

Ethylene producers

Some fruits emit far more ethylene gas than others. Apples and bananas top the list. Other fruits that produce a lot of ethylene include:

• avocados
• figs
• mangoes (and most other tropical fruits)
• melons
• mushrooms
• pears
• potatoes (not fruit, but still a big ethylene producer)
• stone fruits (apricot, peach, nectarine, plum, etc.)
• tomatoes (yes, tomatoes are fruit)

Other fruits stored near near these ethylene producers will ripen faster that they normally would. Blueberries and cherries have very little ethylene gas, and no real impact. Some fruits and vegetables are particularly sensitive to the effects of ethylene gas. They will over-ripen and start to rot when exposed. These plants need extra protection:

• asparagus 
• broccoli
• cabbage
• cauliflower
• citrus
• cucumber
• eggplant
• green beans
• leafy greens (lettuce, spinach)
• parsley
• peas
• peppers
• squash
• sweet potatoes
• watercress

Put ethylene gas to work for you

Placing a piece of fruit in a paper bag allows you to take advantage of ethylene gas. The paper holds the ethylene gas closer to the fruit, speeding the ripening process. Plastic bags do not work, as they trap moisture that can lead to rotting. To slow the ripening of neighboring fruits, many sellers place waxed cloth or plastic over the stem end of bunches of bananas.


Other sources of ethylene
​
Ethylene gas is not just from plants. It is manufactured for agribusiness. It is also the byproduct of your car’s engine, natural gas leaks, welding, and some manufacturing processes. The discovery of ethylene gas occurred over 100 years ago, when someone noticed that trees growing near gas street lamps kept dropping their leaves faster than other trees. 


Maybe that’s why my store-bought strawberries go from nearly perfect to inedible overnight…