Yes, the common knowledge that bananas can speed up the ripening of other fruits is entirely true and based on a natural biological process. Ripening is the transformation a fruit undergoes after reaching maturity, resulting in changes like softening, a shift in color from green to vibrant hues, and the conversion of starches into palatable sugars. This accelerated change is a direct consequence of a communication system between plants. Ripe bananas are active participants in this communication, influencing nearby produce.
The Science of Ethylene Gas
The mechanism behind this influence is a simple, colorless, and odorless compound known as ethylene gas, a naturally occurring plant hormone. Bananas, along with several other fruits, produce and release this gas as a signal to trigger and accelerate their own ripening.
Ethylene binds to specific receptors within the fruit’s cells, initiating a cascade of biochemical reactions. These reactions involve the production of enzymes that break down the fruit’s cell walls, causing the noticeable softening of the flesh. Simultaneously, other enzymes convert complex starches stored in the fruit into simple sugars like glucose and fructose, increasing sweetness and flavor. Since ethylene is a gas, it easily diffuses out of the banana and acts on surrounding produce, sending a signal to nearby fruits to begin their own ripening process.
The production of ethylene is considered autocatalytic in these fruits. This means the initial release of the gas stimulates the fruit to produce even more of it, rapidly accelerating the cycle.
Distinguishing Reactive and Non-Reactive Fruits
Not all fruits respond to the ethylene signal in the same way, which is why fruits are classified into two main categories: climacteric and non-climacteric. Climacteric fruits are those that experience a burst of ethylene production and respiration after harvest, enabling them to continue ripening even when detached from the plant. These are the fruits that are responsive to the ethylene gas released by a banana.
Examples of climacteric fruits include avocados, apples, pears, peaches, mangoes, and tomatoes. These fruits are often picked when mature but still firm and green, allowing for easier transport before they are ripened near the point of sale.
Conversely, non-climacteric fruits do not exhibit this post-harvest surge in ethylene or respiration and do not ripen further once they are picked. Non-climacteric fruits are largely unaffected by external ethylene, meaning placing them next to a banana will not hasten their maturity. This category includes berries, citrus fruits like oranges and lemons, grapes, and pineapples. They must be harvested only when fully ripe, as their quality will not improve afterward.
Controlled Ripening and Storage Techniques
This knowledge of ethylene gas allows for simple, effective techniques to manage fruit ripening at home. To actively speed up the ripening of a climacteric fruit, place it near a high-ethylene producer, such as a ripe banana or apple. The most effective method is to place the unripe fruit and the banana together inside a loosely sealed paper bag.
The bag traps the emitted ethylene gas around the fruit, concentrating the hormone and significantly accelerating the ripening signal. However, to slow down ripening and extend the shelf life of climacteric fruits, the opposite action is necessary. Storing them in a cool, well-ventilated area, or placing them in the refrigerator, reduces their metabolic rate and slows the effects of ethylene.