Science Of Ripening: Why Do Bananas Change Color When Ripening?

At the molecular level, there is cell division, as well as starch to sugar conversion, translating green hard bananas to sweet and sumptuous yellow ripe bananas, enticing frugivores and humans alike.

Bananas are not a delicacy exclusive to our primate cousins. We, as a global civilization, have been consuming bananas for centuries. Today, in our highly industrialized society, we conduct large-scale import and export activities involving these delectable fruits. In fact, bananas are the best-selling item at Walmart, beating out the likes of Coke and Pepsi—the retailer moves around 1.7 billion pounds of bananas every year. Annually, an average American consumes about 27 pounds of bananas, roughly 90 fruits per person.

People like ripe bananas, so special ripening chambers exist where imported bananas are immediately kept so that they reach the market in a ripe and delicious form. We will look into both the contemporary and ancient methods of banana ripening and preservation in this article, in addition to uncovering the science behind the changing color of ripening bananas.

Science Of Fruit Ripening

When we talk about local produce, a lot of banana stock is still raw when sold to consumers, and in the case of large Cavendish bananas, being raw means being green in color. We only eat bananas when they turn yellow, so this color change is an important indicator of ripeness. The question is, what causes this color change when bananas ripen?

Ethylene gas is a simple molecule C₂H₄ that is also released by combustion sources such as vehicle exhaust. It is a master manipulator of ripening processes in fruits. In several plants, ethylene triggers both flowering and fruit ripening. It is the prime suspect behind the fruit developing its color, aroma and texture.

The surge of ethylene leads to the transformation of a hard green banana into a tender, tasty and sumptuous fruit.

This highly orchestrated process culminates in the zone of peak attraction. After this, decay sets in, wherein yellow bananas start becoming spotted and yellowish-black flecks become more prominent. The self-destruction stage called senescence then begins, and the banana turns black with intermittent yellow patches. The banana, at this point, is no longer in a state to be consumed.

How Do Bananas Change Color?

The color shift from green to yellow is, at its heart, a story of two pigments. Unripe banana peels are packed with chlorophyll, the same green pigment that powers photosynthesis in leaves. Hidden underneath are yellow and orange carotenoid pigments—mainly lutein, alpha-carotene and beta-carotene—that have been there all along, simply masked by the abundant chlorophyll.

When ethylene kicks the ripening machinery into gear, the fruit ramps up production of an enzyme called chlorophyllase, along with a cascade of other chlorophyll-degrading enzymes. These enzymes systematically dismantle the chlorophyll molecules in the peel into colorless breakdown products. As the green curtain falls away, the carotenoids that were sitting in the background finally get to take center stage, and the banana takes on its familiar sunny yellow hue.

Temperature heavily influences this color change. Studies show that bananas ripened at a comfortable 18–24°C develop a clean yellow color, but bananas held above 30°C often stay green even as their flesh softens and sweetens—a phenomenon known as "green ripening" caused by incomplete chlorophyll breakdown.

There is one more curious twist. In 2008, chemists led by Bernhard Kräutler at the University of Innsbruck discovered that ripe yellow bananas glow bright blue under ultraviolet light. The glow comes from fluorescent chlorophyll catabolites (FCCs)—the long-lived breakdown products of chlorophyll—accumulating in the peel. Green, unripe bananas don't fluoresce, so the intensity of the blue glow actually tracks how ripe a banana is.

Do Bananas Go Bad In The Refrigerator?

If by “go bad” you mean that does the banana peel turn ugly brown and spotted, then yes, they do go bad in the refrigerator. However, if you also assume that the inside gets mushy and distasteful, that’s not correct. Surprisingly, despite the banana peel quickly turning dark brown/black inside the refrigerator, the part you eat remains good and edible. In fact, Chiquita and Dole, the two most respected banana-producing companies in the US, recommend this to make the banana last longer in its ripe phase.

Storing bananas in the refrigerator once they reach optimal levels of ripeness, NOT BEFORE, will dramatically impede the conversion of starch into sugars, almost to the point of stopping the ripening progress.

The outer peel of the banana starts appearing brown or black because the polyphenol oxidase enzyme in the peel reacts with phenolic compounds in the presence of oxygen to form dark melanin-like pigments. Surprisingly, besides the unappetizing brown-black peel, there won’t be much negative effect on the core flesh of the fruit. Pare the dark peel off and throw it away. What you’re left with is the flesh of a banana that is still quite edible and sweet.

There is a caveat though… Don’t refrigerate the bananas before they’ve reached the edible level of ripeness. Chiquita warns that if you refrigerate an unripe banana, they may fail to resume the ripening process even after being brought out of the refrigerator to room temperature.

Now that you know the science behind the ripening of bananas and the reason for its color change, let’s look at how, throughout history, humans have hacked the process of banana ripening and what contemporary methods are used today for that same purpose.

How Our Ancestors Hacked The Ripening Process

The power of ethylene gas, the main mastermind behind the fruit’s ripening, has been used by humanity for centuries. Ancient Egyptians used to slice climacteric fruits like figs to trigger the discharge of ethylene gas to expedite the ripening process of fruits like banana. Chinese farmers, on the other hand, used to ripen pears by burning incense sticks in storerooms filled with freshly harvested fruits. Scientifically speaking, the adage “one bad apple spoils the lot” refers to how the discharge of ethylene gas from a decayed apple (or any other climacteric fruit for that matter) will promptly ripen other apples in the proximity—and eventually lead to their decay as well.

Based on the ripening, fruits can be divided into two classes: climacteric and non-climacteric. Climacteric fruits are those that can continue to ripen even after being plucked from the tree. Climacteric fruits manifest a burst in respiration, which is technically called a climacteric rise, and thus are called climacteric fruits. This climacteric rise represents a spike in ethylene production as they ripen. Some popular examples of climacteric fruits are bananas, apples, papayas, avocados, mangoes, pears, figs, peaches, etc. Non-climacteric fruits—such as grapes, pineapples, strawberries and other berries, cherries and citrus fruits like oranges and lemons—are relatively docile in terms of their emission of ethylene. Generally, non-climacteric fruits attain full ripeness before being picked, and in most cases would cease to ripen after being detached from the plant.

Contemporary Methods Of Controlling The Ripening Process

The ethylene gas comes in handy for banana cultivators, distributors, and sellers. Generally, for the distributors, the worst thing would be a pack of fully ripe yellow bananas, because they run the imminent risk of senescence—a decaying phenomenon we covered earlier.

Distributors generally pick bananas a week or two early, when they aren’t ripe—but are instead green and hard. They are shipped in this stage, as it gives distributors breathing room for transporting bananas to the warehouses without bruising and staling. Warehouses are often controlled rooms with precise temperature, oxygen, and carbon dioxide levels to further delay ripening, if required. It’s similar to putting fruit in sort of a hibernation until they reach retailers or supermarkets.

Distributors tactfully use ethylene gas to partially ripen fruit before their final distribution to the market if they are hard and green. Industrial ethylene used for this purpose is produced inside the ripening room by catalytic generators that convert liquid ethanol into ethylene gas. Most commercial banana cultivars only need around 100 to 150 PPM (parts per million) of ethylene for 24–48 hours at 15–20°C and 90–95% relative humidity to ripen uniformly. Carbon dioxide levels in the room are kept below 1%, since higher CO₂ blunts ethylene's effect and delays ripening.

It’s also interesting to note that the whole setup of the supermarket’s fruit and vegetable section is designed to optimize their freshness. Aisles of supermarkets are tactfully engineered, keeping ethylene in consideration. As ethylene gas can lead to decay in non-fruit parts, like lettuce, asparagus, etc. they are generally kept away from fruits that are notorious for emitting ethylene.

Conclusion

So, the transition from hard green to ripe yellow to stale black is a tightly orchestrated set of biochemical and physiological processes—ethylene gas signals the peel to dismantle its chlorophyll, and the carotenoids hiding underneath finally show through. By tinkering with ethylene, humans have learned to hack the timing of this process so bananas reach our supermarkets at peak edibility.

The Cavendish—the variety behind almost every banana you find at the store—accounts for around half of all bananas grown worldwide and roughly 95% of the global export trade. It also faces an uncertain future: a soil fungus called Fusarium Tropical Race 4 (TR4), the modern strain of Panama disease, has been steadily spreading and was confirmed in Ecuador (the world's largest banana exporter) in late 2025. Researchers in Taiwan and elsewhere are racing to develop TR4-resistant cultivars, so the next time you watch a banana on your counter turn from green to gold, you're witnessing a piece of food chemistry that scientists are also working hard to keep on the menu.