How do banana bags work?

How do the yellow banana bags work? i.e. they stop bananas from going brown in the fridge?

– Shelley

What is a banana bag?

“Banana bag” can refer to IV bags containing vitamins and minerals used in intensive care – but in the case of this question, it’s a polyester bag with a drawstring used for storing bananas. These products typically claim to provide “the right amount of insulation and air” to keep bananas fresh for up to two or three weeks in the fridge.

Bananas 101

Bananas are a well-known tropical fruit. Botanically, they are the seedless berries of flowering herbaceous plant species in the genus Musa, native to tropical Southeast Asia.

Bananas are what is known as a ‘climacteric’ fruit. These are fruits that continue to ripen after picking, a process accompanied by changes in colour, flavour and sweetness. Green bananas store energy as starch, a long carbohydrate polymer that doesn’t taste sweet, but can be good to eat after cooking.

When a banana is exposed to the plant hormone ethylene, it starts to ripen. Respiration  – the process by which carbohydrates and oxygen are used to generate energy, producing CO₂ – increases dramatically. The fruit also begins to produce its own ethylene, further accelerating the ripening process. The stored starch is converted into simpler sugars, which taste sweet.

This means that bananas can be picked, shipped and even bought while still green and still ripen normally. Other climacteric fruits that can be handled this way include avocadoes and pears.

By contrast, non-climacteric fruits like berries and citrus fruit ripen gradually while they are attached to the plant. They need to be harvested when ripe, as they don’t get any riper or sweeter once picked.

Ethylene hacking

Putting ethylene-producing fruits in an enclosed space helps to concentrate the ethylene and speed up ripening. One well-known strategy is to put bananas or avocadoes inside a paper bag to ripen faster. It’s generally not recommended to store bananas in an ordinary plastic bag, as this traps moisture.

If you’d rather achieve the opposite, wrapping the banana stems – from which most of the ethylene is released – in plastic wrap can help protect the rest of the fruit from ethylene exposure and slow down ripening, according to major banana producer Chiquita.

So how do the bags work (or do they work at all)?

The information available about these products isn’t very detailed, and anecdotal reviews seem to be mixed.

For example, a 2013 Guardian article on food gadgets reported that a banana bag did keep a bunch of bananas edible for noticeably longer than a bunch left in a fruit bowl. Banana bag reviews on Amazon include many customers reporting good results, but also a sizeable minority claiming that the bag didn’t work for them.

Horticulture expert Dr Jenny Ekman, from Applied Horticultural Research, advises consumers to maintain a healthy scepticism towards this kind of product.

“There have been many seemingly magic bags and sachets commercialised over the years which claim to somehow increase fruit and vegetable storage life,” she says. “However, they are rarely accompanied by independent data proving any such thing.”

However, she did have some suggestions for how the bags might be working.

Normal refrigerator temperatures (approximately 5°C) can damage bananas. “Like other tropical fruits and vegetables, they are not adapted to such cold conditions,” Ekman explains. “The result is breakdown of the cell walls and the browning that quickly appears, primarily in the skin rather than the flesh.”

However, bananas will generally continue to ripen within a few days if left out at room temperature, especially during warm weather.

The banana bag might be helping by creating a kind of Goldilocks environment for the bananas – not too warm, not too cold – between the undesirable extremes of the fridge and the kitchen counter.

“Just like us, bananas ‘breathe’ in oxygen and release CO₂,” says Ekman. “This produces heat. I imagine this bag is attempting to capture that heat, so that even though the bananas are in the fridge they will remain warmer than 5°C.

“If the temperature inside the bag is, say, 12°C, then you will indeed reduce the rate of ripening while not going so low as to cause chilling damage.”

That seems to fit well with manufacturers’ explanations that the product uses “insulation” to keep bananas fresh. However, Ekman warns it’s a delicate balance that can’t be maintained indefinitely.

“Inevitably, they will eventually cool to the same temperature as the fridge, and chilling damage will occur.”

The bags might also help maintain a humid environment for the bananas, which keeps the skins from drying out.

The verdict

Overall, it’s not 100% clear how the banana bags work, but we have some decent ideas.

If you have a bag and find it’s working well for you, by all means keep using it. If you’re sceptical, there are other strategies you can try to help keep your bananas fresh.

Or you could go the time-honoured route of treating overripe bananas not as a tragedy, but as a good excuse to bake muffins.

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