The white powder is most likely Calcium Hydroxide [‘slaked lime’] which can be used in cooking as a substitute for baking soda. It is harmless.
Calcium Hydroxide is a product of the hydrolysis of Calcium Carbide which was likely used to also produce Acetylene, which is quite similar to the natural ripening agent Ethylene.
Is calcium carbide used to ripen bananas in Australia? How do you know?
It won’t be from Calcium Carbide. See @BrendanMays post:
Calcium Carbide use within food production in Australia is a internet myth. Australia also doesn’t import bananas (due to risk of introduction of pest and dieases to our own industry) so it is impossible for this to be the source.
Most baths/dips at farms are only topped up when needed (to reduce water use) and there is a potential for the accumulation/concentration of salts within the wash water. Calcium carbonate (which is also a salt of metal calcium) could also be a source, along with other salts (other metal salts of magnesium, calcium, sodium etc) present in the water used for washing. One doesn’t need much CaCo3 to leave visible residues on the fruit.
Bananas in Queensland grow mainly along on the coast strip and the groundwater in these areas do contain salts of varying concentrations. I would suspect that groundwater or dam water would be used for washing on a farm over potable water (rain collected or mains) due to cost and also availability.
While it may not be the source of the white powder on all banana farms, it has the potential to be a source on some.
It would be interesting to have the powder analysed to see what it is (a very easy exercise to do at a testing laboratory).
Ethylene is a natural ripening agent, inducing black spots and streaks in bananas.
Bananas are renowned to be relatively large producers of Ethylene. Woolworths would want to extend the life of their bananas in storage. This could be achieved by converting all the outgassed Ethylene to an inert byproduct or modify the storage environment to inhibit the production of Ethylene. If the chemically similar acetylene gas was in the storage environment, that might tip the equilibrium to reduce the natural outgassing of Ethylene. With less Ethylene, the stored bananas would last longer.
I wouldn’t call it harmless! It causes pretty bad skin irritation and can seriously damage your eyes, as it is a strong alkali.
AKA Builders or Hydrated lime.
In any case, I have no idea why it would be applied to bananas, which are ripened with ethylene gas by enclosing the bunch in a plastic bag to concentrate the gas, which is given off by the bananas
The bananas produce their own ethylene so changing atmosphere around the bananas could have limited impact on their ripening as the natural gas would be permeating through the fruit. Not using ethylene gas would slow ripening as ripening would only be triggered by the natural ethylene and not the additional ethylene gas (causing accelerated ripening).
Fruits natural ethylene production can be slowed by measures such as cooling…which is how fruit like apples can be stored to long periods of time. Bananas aren’t stored for long periods prior to sale (I recall seeing somewhere that significant cooling can affect the skin appearance making them less attractive to the consumer.
I have just come across this…which might also be the white powder observed on the bananas… As the article is from 2012, this technology/research could have been adopted by now.
It’s all a matter of concentration: a little may be harmless; and a lot may be poisonous.
And, if I was Woolworths, I’d wanna MINIMISE the amount of ripening by Ethylene.
Nothing to do with Woolworths, I’m talking about banana plantations, ie the growers use the bags.
Can you provide a reference for using Ca(OH)2 as an alternative for NaHCO3 (or baking powder=30%NaHCO3)? I’ve only heard about using Potassium bicarbonate as an alternative.
I grow bananas sometimes in Adelaide, I have never seen a white powder on them.
Finally a subject that I actually know about and I am a week too late with this answer too. But I am going to contribute to this subject even though it is not a lot. I had a lot more info on last week’s topic of cold storage of bananas. As most of the contributors were correct in saying that bananas are not kept in cold storge but only kept in cool rooms for a couple of days while they are gassed with ethylene.
I used to grow bananas commercially for over 20 years in Northern NSW. And since I haven’t grown them for 20 years, practices may have changed but all the time we were growing them, as we cut the hands off the bunch we would place the hands in a vat of water with dishwashing liquid added for a couple of minutes before placing them on the bench to be packed. The reason for this was to stop the sap flowing from the cut end of the hand. So this plus the gassing in the merchants’ cool rooms (approx.13 degrees) used to be the only treatment the bananas received.
And since I haven’t seen this white powder that n3m0 has seen, I can only guess that it is either something that Woolworths themselves have added or industry practices have changed in the last 20 years. (Although they didn’t change much in the previous 20 years!)
I first asked about it almost 30 years ago, and it was a fruiterer, not in Woolies. It’s been around for a long time.
I posted my query, copied below, under the topic " Unwarranted Price Increases" a fortnight ago but never received a response.
"When I was young, there was a business in the Cairns CBD and the signage on the wall read “D. E. Good & Co. Licensed Banana Ripeners”.
However, my very good friend, Mr Google, does not seem to know about it.
Does anyone know why banana ripeners were require to be licensed in the 1960’s and why this practice ceased?"
Does anyone know why banana ripeners, at least in Qld, needed to be licensed?
Perhaps because the white powder killed them all? 
I didn’t start growing bananas until the 1970’s and when I did I sent them to the Sydney Markets but I did send beans & zucchini before then, and I’m pretty sure all fruit & veggie merchants had be be licensed.
I never gave it a lot of thought at the time but I presumed they needed to be licensed to handle food stuff and also because they handled growers money. All fruit & veg was sent to the merchants who only handled it on consignment. They sold the produce to a greengrocer who paid them at the time of the sale and maybe some had 7 day accounts with the merchant. The merchant would then write out cheques to the grower minus their commission & handling and we (the grower) would receive our money about a fortnight later.
So maybe the merchants (banana merchants were also ripeners) needed to be licensed to a) handle food stuff and; b) they had to operate trust accounts. And because of potential pest & diseases, transport & general movement of bananas was carefully controlled as well. But I was not aware that licensing requirements had ceased. Maybe called another name?
So even though it doesn’t answer Fred123’s query directly, this information may help clarify it a bit.
Thanks @OldRed - very interesting to read your perspective. And don’t worry about the timing, we welcome people to contriibute to our open topics at any time.
Just to add to this conversation, I found it intriguing, and I knew that there was a website promoting Australian bananas. So on March 8th I went to australianbananas.com.au and contacted them with a question about the white powder. Soon after I received an email saying they would get back to me, and 2 days ago I received a reply.
It said ‘Without seeing the fruit in question, it’s impossible to provide a definitive answer. However, some banana growers do use a mixture of talc (the same as baby powder) and insecticide powder for controlling bunch pests. This is applied at bagging time (11-12 weeks before harvest). The insecticide gradually degrades in the environment well before harvest and, any residual talc is normally rinsed off in the tubs of water prior to packing. Occasionally, a small amount of harmless talc residue is left. This residue is harmless both for consumers and for composting.’
So there it is, probably talc, which is harmless, and maybe some unnamed insecticide that was with it, which may or may not have degraded in the environment. So are the skins OK to use in your compost? If any white powder is visible I would probably at least wash it off first before sending it to compost.
I would say yes to composting and no to washing.
There are strict withholding periods for fruit and vegetables which have been subject to a pesticide control (these include for both synthetic and organic treatments). These withholding periods are to ensure that there is no known risk to the consumer from the treatment and the subsequent fruit/vegetables consumption.
If the bananas have been treated with a pesticide, and the withholding period has been followed, there would be no issue in eating the bananas or placing the banana skins into a compost bin.
If for example the withholding period was not followed and there were still pesticide residues on the skins, I wouldn’t be washing the skins as this likely to increase the likely exposure to those handling the skins and also spread the pesticide residues to places to where one might not want them. As composting usually takes 6+ weeks, any residual persticides are likely to have been well and truely degraded by the time the compost is used.
As a more general precaution, nearly every F&V product we consume is exposed to surface contamination from handling, the storage environment and importantly sitting on the shop shelves. No one I know has ever sneezed or coughed in the supermarket, right?
Don’t forget the checkout counter and everything else that has passed over it.
White powder or nothing vissible, the previous advice about washing your F&V may be the best.
