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Hibernating Apples

Over 200,000 cartons of apples are hibernating in a new nitrogen storage facility run by the NZ Apple & Pear Marketing Board in Hastings.

The facility, commissioned from NZ Industrial Gases, uses a molecular sieve to sort out atmospheric components. Oxygen is trapped by the adsorptive material and nitrogen is passed through the pores into the 16-room storage area.

"The degree of porosity is demonstrated by the fact that these adsorption materials may have surface areas of 1,500 square metres per gram of material -- the area of ten average NZ homes on a particle [the] size and weight of a rice grain," notes Helen Parkin, NZIG gas systems specialist.

This selective adsorption produces a controlled atmosphere with a nitrogen content of 98%, compared to the more usual 78%. The facility is computer monitored to ensure that the correct level is maintained.

The idea of having more nitrogen and less oxygen is to slow the apples' "breathing". When the fruit takes oxygen, it uses use sugars to produce carbon dioxide and water. This causes it to lose flavour and texture. Making it breathe more slowly means the fruit lasts longer and stays in better condition. Storing apples under controlled atmospheric conditions can prolong their edible life by four to six months.