The Claim and Our Verdict
The claim: A banana has been chemically ripened if it is brown spotted with a green stalk. If the stalk is black, then the banana is naturally ripened.
- Overheated bananas or those with bruises or cuts may develop brown spots on the peel. Crown rot disease can cause banana stems to turn black. Meanwhile, green stems can be found in both naturally ripened and ethylene-treated bananas.
- Liu Yuanshuai, associate professor of Engineering Education, Department of Chemical and Biological Engineering of The Hong Kong University of Science and Technology, told HKBU Fact Check that consumers cannot judge whether bananas have been chemically or naturally ripened from their appearance, because ethylene is the ripening agent of both methods.
- Studies have shown that there is no difference in terms of biochemical composition and sensory quality between bananas ripened using the two methods.
Our verdict: The claim that the color of banana stems is an indicator whether they have been chemically ripened is groundless.
A tweet published July 12, 2022 claims that banana’s stem color indicates whether it has been chemically ripened. The traditional Chinese-language tweet translates as, “A banana has been chemically ripened if it is brown spotted with a green stalk. If the stalk is black, then the banana is naturally ripened.”
As of the publication of this report, the tweet had been shared 27 times, three times with quote, and it had received 64 likes.
1: Overheating or bruising could cause brown spots on bananas.
According to articles on the Encyclopedia Britannica website and the official website of Dole plc, an American food company and the world’s largest supplier of fresh vegetables and fruits, the life cycle of a banana starts with deep green, changes to yellow, and ends at brown. Like most fruits, bananas produce and react with an airborne hormone called ethylene that helps to signal the ripening process. However, unlike most fruits, which produce only a small amount of ethylene in the ripening process, bananas generate a large amount, causing the yellow pigments in them to decay into brown spots in a process called enzymatic browning.
HKBU Fact Check has contacted the Center for Food Safety under the Food and Environmental Hygiene Department (FEHD) of the Hong Kong SAR to inquire for details about the ripening process of bananas. FEHD replied, “Ethylene is a gaseous phytohormone that plays an important role in regulating the ripening process of various fruits such as bananas, apples, pears and melons. It can be produced naturally by fruits that start to ripen or from artificial sources such as ethephon.”
Therefore, ethylene is a growth regulator that promotes banana ripening. It can be produced naturally or artificially applied to stimulate the ripening process. Ethylene causes bananas to develop brown spots as they ripen.
However, according to the Market Inspection Instructions for Bananas published by the U.S. Department of Agriculture, bananas can develop numerous brown spots in an overheating environment. An article on the website of Encyclopedia Britannica points out that the natural browning (developing brown spots on the peel) is also observed when bananas become bruised. A damaged or bruised banana will produce an even higher amount of ethylene, ripening (and browning) faster than if undamaged. Therefore, overheating and bruising can cause brown spots on bananas.
2: Crown rot disease could cause banana stems to turn black.
The Better Bananas project is an initiative of Australia’s National Banana Development and Extension Program. It aims to provide Australian banana growers and industry stakeholders with the latest information and results from research and development projects. The project is an initiative of the Queensland Department of Agriculture and Fisheries and Hort Innovation, supported by the Australian Banana Growers’ Council.
According to the Better Bananas website, crown end rot (CER) of bananas is a serious cause of post-harvest quality loss for banana fruit. A photo captioned “Crown end rot extending into banana fruit” shows a bunch of bananas with black stems. In addition, a similar photo of bananas with crown rot was also found on the official website of the Postharvest Center of the University of California, Davis. Crown rot is a disease caused by one or more fungi, according to the website.
Therefore, crown rot can be one of the reasons for blackening of banana stems. The claim that “If the stalk is black, then the banana is naturally ripened” is false.
3: Consumers cannot judge whether bananas are chemically or naturally ripened only from their appearance.
Liu Yuanshuai, associate professor of Engineering Education, Department of Chemical and Biological Engineering, The Hong Kong University of Science and Technology, told HKBU Fact Check that consumers cannot judge whether bananas are chemically or naturally ripened only from their appearance, because there is no difference between the bananas ripened under either approach. Both approaches use ethylene that stimulates the ripening process.
Liu explained the process of ripening bananas in detail: “Bananas are harvested when they are still unripe, which is more convenient for transportation, because it has strong texture and insensitive to any collision. Antifungal chemicals may be placed on the two ends, which is more easily accessible than the skin for microbes. After the transportation, bananas are stored in a controlled atmosphere (temperature, humidity, carbon dioxide/oxygen content, etc.) Several days before the retailing, ethylene will be introduced to ripen the bananas, making it yellow and soft.”
As for whether artificial or natural ripening of bananas affect human health, Liu said that there is no difference between bananas ripened under the two methods, so consumers do not need to worry about safety issues. The FEHD also told HKBU Fact Check: “Ethylene is a common plant growth regulator… If farmers properly use registered pesticides (including plant growth regulators) in accordance with Good Agricultural Practices, residues of plant growth regulators can be minimized, and the food safety risk is extremely low.”
A study published in 2019 in the International Journal of Food Science & Technology, states that, in most studies, there is no difference in biochemical composition and sensory quality between bananas treated with chemicals that induce ripening and naturally ripened bananas.
Similar claims have also been debunked by Reuters, Snopes and Full Fact. Dr. Maricruz Ramirez Sanchez of the University of Costa Rica’s Agronomy Research Center told Snopes that green stems are seen in both naturally ripened and ethylene-treated bananas. There are no visual or chemical tests to confidently assess whether a banana has been ethylene-treated or naturally ripened.
Therefore, it is impossible to judge whether a banana has been chemically ripened only based on the color of its stem.
The claim that the color of banana stems is an indicator of chemical ripening is groundless.
- Dole, “Why do bananas go brown?”
- The U.S. Department of Agriculture, “Market Inspection Instructions for Bananas,” Apr. 2004.
- Better Bananas
- Better Bananas, Crown end rot.
- Postharvest Center, “Fruit Produce Facts English – Banana,” published in November 1996.
- National Library of Medicine, “Induced Ripening Agents and Their Effect on Fruit Quality of Banana,” May 2, 2019.
- Reuters, “Fact Check-Shoppers cannot spot whether bananas are ‘chemically ripened’,” Apr. 20, 2021.
- Snopes, “Can You Tell If a Banana Is “Chemically Ripened” by Looking at It?” May 28, 2019.
- Full Fact, “You can’t tell how a banana was ripened by looking at it,” June 22, 2021.