Bananas ripen quickly because they release ethylene, a natural plant hormone that speeds the softening and browning process. Much of this gas escapes around the crown where the stems meet, which is why one popular storage trick involves wrapping that area tightly with cling film.

Covering the crown may slow the spread of ethylene slightly, helping the bananas stay yellow and firm for longer. For better results, separate the bananas first and wrap each individual stem. However, claims that this method always adds exactly ten days are exaggerated. Ripening speed still depends on how mature the bananas were when purchased, room temperature, humidity, and nearby produce. Utah State University Extension includes wrapping the crown with plastic wrap among its tips for slowing banana ripening.

Keep unripe bananas at room temperature and away from direct sunlight, ovens, and other warmth. Store them separately from apples, avocados, and tomatoes because these fruits also release ethylene and may accelerate ripening. Bananas themselves produce ethylene that can ripen nearby produce faster.
Once bananas reach your preferred ripeness, refrigerating them can slow further softening. The peel may darken quickly in the fridge, but the fruit inside can remain usable for several more days.

So the useful kitchen item is cling film, but it is a helpful slowing method—not a guaranteed ten-day miracle.