Dr Morris, director of Sydney Postharvest Laboratory, said half of Australia's apples were now being treated at farms and warehouses with SmartFresh, a synthetic gas developed and delivered by AgroFresh, owned by agricultural giant Dow. The synthetic gas is also applied In the past, the freshness of apples could be extended by placing them in cool rooms with oxygen reduced to 1 or 2 per cent. The SmartFresh synthetic gas slows down the ripening process further. "There's a special ripening gas called ethylene [that is natural]," he said. "Think of a lock and a key. The ethylene is like a key and all the inside of a fruit, every little cell, has little locks. When the ethylene molecules come in, it picks into the locks and triggers the fruit to ripen and sweeten up," he said.

"But the SmartFresh [synthetic gas] goes into the apple and jams all the locks so the fruit can't respond to ethylene." Shoppers can buy "fresh" homegrown apples year round. But Dr Morris believes the term is misleading and there is a penalty to be paid. "Carefully conducted experiments showed the 1-MCP [gas] reduced the sweetness and aroma of apples, while the fruit looks beautiful on the outside." Dr Morris said the gas could extend the shelf life of some fruit by up to two years. But John Dollisson, chief executive of growers body Apple and Pear Australia, said farmers usually kept their SmartFresh treated apples in cold storage for six to eight months. The chemical has been used for a decade.

"They're a lot better than the alternative, because when an Australian doesn't buy an apple, they go into the next aisle and they buy health foods which are clearly nowhere near as nutritional as apples, are much higher in calories and cost a lot more," Mr Dollisson said. He rubbished suggestions that apples were sweeter and more nutritious three decades ago. "We believe they're as nutritious as the day they went in [the coolroom]," he said. Postharvest and food safety expert from Sydney University, Robyn McConchie, said she fully supported SmartFresh technology that put fruit to "sleep". "It means there's hardly any metabolism going on at all and that includes the amount of sugars, the amount of starch, the amount of vitamin, the amount of polyphenol," she said. "They all remain pretty close to the level of when they were actually put into storage." "Storage organ" vegetables such as carrots and potatoes had low metabolisms and were therefore able to be stored for a long time, she said. "You just need the right temperature to store them in."

Leafy greens such as spinach were "very perishable" and therefore impossible to store for more than a couple of weeks, she said. "The vitamin C content of products like that and other nutrition components decline really rapidly after harvest. Spinach would start to yellow, the chlorophyll will start to break down and you'll see it wilting." A spokesman for Woolworths, the self-declared "fresh food people" company, said selling apples that had been in cold storage for months was no secret. "We make it clear to customers, in store through our staff and signs on product and on our website, when our apples are in season," a spokesman said.