To get to the bottom of this mystery, I reached out to Chris Sheehy, prestige manager for Pernod Ricard Australia, who confirmed what I secretly had assumed all along … it's a load of sh*t.
"Truthfully, the teaspoon has zero effect," Sheehy told me.
Explaining the thinking behind it, Sheehy said: "The theory is that you put a cold spoon into the neck and that makes the air around the spoon colder, so more dense. Because it's denser, the bubbles won't escape past it, so it's almost like an air blanket that sits on top of the bottle so that the CO2 stays inside the bottle."
As part of his role at Pernod Ricard Australia, Sheehy regularly holds tastings for Mumm champagne around the country and has tested the teaspoon theory out himself.
"We've looked at different ways and methods to keep champagne fresh and the old spoon in the bottle trick always comes up the same as if you just leave the bottle in the fridge with nothing in it at all," he said.
So what is the best way to try and keep your leftover champagne fresh?
"If you do have some left, the most important thing is the temperature," Sheehy told news.com.au. "You should never let the bottle warm up and then chill it down again. If you can keep it cold at all times, that will hold the bubbles/carbon dioxide in the liquid.
"The next factor would be how much Mumm champagne is left in the bottle," he continued. "If you've only had one glass from the bottle then there's not much oxygen within the bottle itself, so it will tend to last longer. But if you've only got a small amount left, like one glass in the bottle, it will have been losing its fizz far quicker no matter what you do.
"The rule of thumb for me is if you've got one glass left in the bottle then don't even try and save it, just enjoy it.
"The next factor is the closure system," Sheehy said. "If you do have a champagne stopper, they're relatively easy to find and pretty cheap, keep the bottle nice and cold the whole way through and put the stopper in if you've got at least half a bottle or more left and get it back in the fridge."
Sheehy said that if you keep the bottle cold, have more than half the bottle left and use a stopper, the champagne should stay fresh for another 24 hours.
But if there's less than half a bottle left, the champagne will start to suffer after just four or five hours in the fridge, he said.
"The other option is a champagne preservation system," Mr Sheehy told news.com.au. "We've had preservation systems for wine for quite a while but it's taken them a while to understand how to preserve sparkling champagne.
"At the moment there are some pretty cheap, pretty reliable preservation systems available and what they do is pump a layer of CO 2 into the bottle.
"With a preservation system you can get up to a week of quality champagne from the bottle after you've opened it."
Aussies knock back approximately eight million bottles of champagne every year, 40 per cent of which gets consumed between November to February.
So if you see someone over the next few months putting a spoon into their champagne bottle, you can smugly tell them they're doing it all wrong.
