Ethylene Producing Produce

Some fruits and vegetables will produce ethylene, sometimes called the “plant ripening hormone.” It is a gas that functions as a plant growth regulator and triggers specific events, such as ripening. As the fruit ripens, ethylene causes cells to degrade, fruit to turn softer and sweeter, leaves to droop on plants, and seeds or buds to sprout. You take advantage of this natural, colorless gas when you put a ripe apple in a bag of unripe pears to hasten the ripening process. It’s ripening effect on crops is used commercially for the artificial ripening of the fruits. This has made it possible for tropical fruits such as mangoes and bananas to be harvested green and shipped to distant markets, where they are ripened under controlled conditions.

Some fruits and vegetables are high ethylene producers, others produce very little ethylene and may be sensitive to it. Fruits and vegetables are classified as “climacteric” or “non-climacteric” depending on their response to ethylene.

Climacteric species emit a greater amount of ethylene as they ripen, and after ripening peaks, the production of ethylene gas drops off significantly. Thus, climacteric fruits have a fast period of ripening during which they soften and develop flavor and aroma.

• Climacteric: Climacteric fruits and vegetables continue to ripen off the vine. They experience a rapid increase in respiration during ripening. They also often produce a hormone called ethylene after harvest, which can speed up ripening and senescence. If eaten at an immature stage, these fruits and vegetables taste bland, and the texture is often not as soft as it is meant to be. If left at room temperature they will become sweeter. Common examples of climacteric fruit include apples, bananas, peaches, and tomatoes.
• Non-climacteric: These fruits and vegetables do not continue to ripen off the vine. Once removed, the sugar content will not increase, and so picking at exactly the right time is important for flavor. These fruits and vegetables can still go bad if left out, but they tend to have a longer shelf life than climacteric fruits and vegetables. Examples include: grapes, strawberries, and watermelon.

Some points to note about ethylene gas:

1. Climacteric fruits will continuing to ripen after they are harvested, as you may have noted with green bananas and mature green tomatoes, pears, mangos, peaches, apples, and avocados. Non-climacteric plants, such as leafy and root vegetables, citrus, cherries, and berries, produce very little ethylene and do not continue to ripen after harvest; however, they will soften and rot as they age.
2. Ethylene can cause premature ripening in some foods, while in others it can actually cause damage. To reduce unnecessary spoilage of your produce, do not store ethylene producing fruits and vegetables with those that are sensitive to it. For an example from the lists below, storing ethylene-producing apples with ethylene-sensitive peppers can cause the peppers to overripen or spoil. If spinach, kale, or broccoli (ethylene-sensitive) is stored in the same refrigerator bin as apples, those crops will turn yellow and limp in just a couple of days. You also don’t store potatoes and onions together because the potatoes emit ethylene which will cause premature sprouting of the onions. Fruit that is damaged, such as bruised or punctured, will produce more ethylene, causing the others to ripen, soften and spoil faster; so always use the damaged fruit first and don’t store them with unblemished product.
3. Note that not all fruits and vegetables produce significant amounts of ethylene, nor is all produce sensitive to it. Citrus fruits such as oranges and lemons, for example, do not produce much ethylene and are relatively hardy to it.

Note: Do not store produce in bags or sealed containers. This will trap the gas and cause the produce to ripen faster.

"All you need to do is to put the ethylene-sensitive produce in paper bags, roll them shut, and place them in one crisper," Ferretti says. "Those items that produce large amounts of ethylene should be bagged and stored in a separate crisper."

When it comes to the ripening process and fresh produce, all fruits and veggies fall into one (or more) of three categories listed below. For a detailed table of common fruits and vegetables and whether they are ethylene producing or sensitive to ethylene, see Fruits and Vegetables - Optimal Storage Conditions.

Ethylene Producing Foods

Some fruits ripen after harvest and emit a greater amount of ethylene as they ripen. These are called climacteric fruits. Kathleen Brown, associate professor of postharvest physiology, says most tree fruits produce large amounts of ethylene, particularly apples and pears. Other high ethylene producers include apricots, avocados, cantaloupes, nectarines, papayas and peaches. Certain producers, like bananas, tomatoes, and peppers only start emitting ethylene once verging on overripe. You want to keep them away from non-climacteric produce that is ripe when it is harvested.

Fruits and vegetables that produce large amounts of ethylene gas should be wrapped loosely so that the gas can escape. This will slow the ripening process of the ethylene producers.

Ethylene Sensitive Foods

Some foods are more sensitive to ethylene than others.

Many vegetables are especially sensitive to this gas, which is why we store refrigerated vegetables separate from some fruits. Vegetables that are ethylene sensitive are asparagus, broccoli, Brussels sprouts, cabbage, cauliflower, corn, cucumbers, eggplant, green beans, kale, lettuce and greens, mushrooms, onions, parsley and herbs, peas, peppers, summer squash, and sweet potatoes.

Fruits differ in their sensitivity to ethylene. Fruits that do not ripen after harvest are sensitive to ethylene and are called non-climacteric. These include blueberries, blackberries, raspberries, cherries, grapes, strawberries and watermelon. Citrus fruits vary somewhat. Most ethylene-sensitive fruits are best stored away from ethylene-producing fruits.

It’s quite the paradox, we know, but some ethylene producers can also be ethylene sensitive. “One bad apple can spoil the whole bunch” really does hold true if said apples are stored in a bag or a closed container, effectively trapping the very gasses they give off, leading to speedier ripening.

Produce that is sensitive to ethylene includes:

--Carrots and Parsnips. "Both of these vegetables get very bitter when exposed to ethylene," Ferretti warns.

--Broccoli, Brussels sprouts, cabbage, cauliflower, celery, collards, kale, lettuce and spinach. "These vegetables will turn yellow and go limp from too much ethylene," he says.

--Cucumbers. Ferretti says cucumbers will turn yellow, go soft and develop mushy spots.

--Asparagus. "Asparagus will turn tough or woody," Ferretti says.

--Iceberg Lettuce. "Ethylene causes rust-colored spotting, similar to the injury color you see on lettuce when you cut it with a knife," Ferretti says.

--Squash. All types of squash will develop soft spots and turn yellow from overexposure to ethylene. "Most people don't store winter squash -- like acorn squash -- in the refrigerator, but zucchini and summer squashes can go bad if stored with ethylene producers," Ferretti says.

--Herbs. Parsley, marjoram and mint are the most common herbs that are sensitive to ethylene.

--Apples. Although apples are one of the highest producers of ethylene, the fruit also is sensitive to the gas. Prolonged exposure to ethylene turns apples mealy or less crisp. "Low temperatures reduce sensitivity to ethylene," Brown says. "It's best to store apples in the refrigerator unless they are under-ripe."

Not Ethylene Sensitive