Despite the predictions of James Howard Kunstler and a myriad of other post-apocalyptic commentators, the 3000-mile Caesar salad is still with us.
On this side of the new Millennium the end-times observers were expecting to be scratching a living as detrivores, gradually regressing to an archaic existence as hunter-gatherers. Many of us would not make it, they said. The future would belong to the people who could preserve and store their own food.
Thankfully we avoided Armageddon.
Nevertheless, anyone with a five-a-day fruit and vegetable habit might occasionally wonder how their delicious Granny Smith apples could have survived a year in storage followed by an air trip from Australia; or indeed how those fortnight-old French beans can arrive from Kenya looking as fresh as the day they were picked. How do these comestibles traverse the globe without succumbing to fungal disease and jet lag?
Controlled atmosphere storage – how it works
Food storage and preservation techniques have evolved over millennia. The survival of our ancestors depended on their ability to accumulate enough for the winter; failure would mean starvation. But the modern-day phenomenon of globalisation has generated a demand for contemporary innovation. One of the more successful methods is controlled atmosphere storage, or ‘CA’, a process in which the oxygen, carbon dioxide and nitrogen are regulated.
CA storage typically reduces the oxygen in an airtight container or sealed room by carefully introducing nitrogen. Fruit and vegetables kept under these conditions are prevented from ripening at their normal rate; in effect, the ageing process is slowed down. Goods stored in CA can be preserved for up to four times longer than by other methods, providing that the gases are continuously monitored and adjusted in response to the metabolic activity of the produce.
For long-term storage of apples the oxygen level is reduced from 21 per cent to just one or two per cent. In addition, the carbon dioxide can be increased from an atmospheric level of 0.04 to as much as ten percent. (Higher CO2 inhibits the production of ethylene, a naturally occurring ‘ripening’ gas, thereby delaying—or postponing—the process of maturation.) Temperature and humidity of the space are also regulated to maintain the optimum conditions for preservation.
CA storage is additionally used in containers that hold dry goods such as beans or grain. The gas mixtures for these applications usually include a greater proportion of carbon dioxide; CO2 has an advantage over other gases because it can kill most bacteria and it helps to eradicate mould, insects and rodents. CA storage is therefore considered to be a safe, environmentally acceptable method of pest control—in other words, a fumigant that leaves no harmful residue.
The dangers of controlled atmosphere storage
Many successful technologies, however, have an intrinsic weakness. This could be either a negative side-effect, a toxic by-product, an environmental risk or a hazard. CA is no exception. By reducing the oxygen level in a container or an enclosed space you create an atmosphere that is harmful to human health. If you increase the level of carbon dioxide then that, too, is dangerous. Either of these situations is potentially lethal for anyone entering the area.
The dangers of CA storage were highlighted by a tragic incident on a Hampshire fruit farm in 2013. This case was in the news again recently, as the trial at Winchester Crown Court finally reached its conclusion. On 1 July 2015 the farm manager was convicted of manslaughter and jailed for two and a half years; two of his employees had died after being encouraged to enter a nitrogen-filled apple storage unit. The unit contained an oxygen level of just one per cent.
Author: Paul Smith, Technical writer
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