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RE-EVALUATING THE CO2 LEVELS FOR CA APPLE STORAGES 



W.J. Bramlage 

 Department of Plant and Soil Sciences 



In 1973 ( Fruit Notes , Sept. -Oct.), we reported that recommen- 

 dations for COo levels in CA apple storages were being re-examined. 

 Since then, we and others at a number of different experiment sta- 

 tions have been testing the use of short periods of high CO2 at 

 the beginning of CA, as a means of delaying ripening, and especial- 

 ly softening during and following CA storage. 



The widespread interest in this technique arises from the ex- 

 cellent results that Dr. H. Melvin Couey and his colleagues of the 

 U.S.D.A. in Wenatchee, Washington have obtained on 'Golden Delicious.' 

 They began high CO tests in 1971, and their technique has been so 

 successful that it was given an industry-wide test on Washington 

 'Golden Delicious' last year. Their treatment consists of simply 

 raising the CO2 level to 201 (in 4-5% O2) for the first 8-10 days of 

 CA or to 15% (in 4-51 Oy) for the first 15 days, followed by the 

 normal CA atmosphere. They have found the 'Golden Delicious' trea- 

 ted in this way to be 2 lbs firmer than normal CA fruit in February, 

 and to continue to be significantly firmer and have a better flavor 

 throughout the remainder of the storage season. 



The possibility that 'Mcintosh' quality after storage might al- 

 so be improved by a similar treatment has been pursued at several 

 experiment stations. We have conducted substantial tests during 

 the past 2 storage seasons with mixed results, but these tests have 

 illustrated the potentials for both benefit and damage. 



In the 1973-74 storage season, we treated 'Mcintosh' and 'Red 

 Delicious' with high CO2 . Using an Arcat* generator, we "pulled 

 down" O2 to 3% but did no CO2 scrubbing. The CO2 level during pull- 

 down rose to about 9%, and during subsequent weeKs slowly rose to 

 about 11%. Apples kept at these high CO^ levels at 38°F for up to 

 9 weeks before being transferred to a normal Mcintosh atmosphere of 

 3% Oy, 5% CO2 and 38°F, and samples were examined for quality in 

 January, March, and May. There was no benefit to 'Mcintosh' from 

 these treatments, and while 'Delicious' held in high CO2 for 3,6 or 

 9 weeks were firmer in January than ones in normal CA, the differ- 

 ences disappeared during later storage. We concluded that 9% CO2 

 at the beginning of CA was of no value to 'Mcintosh, ' but we also 

 were impressed by the lack of any injury to the fruit, even after 

 9 weeks exposure to 9-11% CO2 . This suggested that the apples had 

 more tolerance for CO2 than we had believed. 



In the 1974-75 season, we decided to test this tolerance with 

 some extreme treatments on 'Mcintosh' and 'Cortland.' Again, O2 

 was "pulled down" without scrubbing and CO2 was then added to the 



*Trade name 



