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I 



CO2 TREATMENTS FOR 'McINTOSH* AT THE 

 BEGINNING OF CA STORAGE 



William J. Bramlage 

 Department of Plant and Soil Sciences 



Perhaps you have read about the CO2 treatments that are being 

 used in Washington to slow dovm softening of 'Golden Delicious' 

 apples in CA storage. This procedure has gotten a lot of publi- 

 city and is working very well in commercial storages in that state. 

 If you have read any of these reports, you have surely wondered if 

 the same treatment will work on 'Mcintosh'. So have we, and in 

 earlier Fruit Notes articles (Sept-Oct, 1973 and Sept-Oct, 1975) we 

 reported results of our preliminary studies with this procedure. 

 In 1975, we also reported that a large-scale test was to be conduc- 

 ted to determine the feasibility of this "COo pretreatment" of 

 'Mcintosh*. This test has now been completed and its findings can 

 be reported. 



The 'Golden Delicious* treatment simply consists of raising 

 the CO2 level in the storage to 15% during the first 8 to 10 days 

 of CA storage, then scrubbing it down to the normal CO2 level for 

 CA storage. It results in much slower softening of the apples and 

 allows the growers to market crisp fruit into late spring and early 

 summer. In preliminary tests with 'Mcintosh', both in Massachusetts 

 and in other areas where this variety is important, the trials in- 

 dicated that softening of 'Mcintosh' could also be slowed down by 

 CO2 pretreatment, but that there was considerable danger of COo in- 

 jury from the treatment. To evaluate as broadly as possible the 

 potential benefit and potential danger from such a treatment, a co- 

 operative study was made at 5 locations where 'Mcintosh' is an im- 

 portant variety: Massachusetts, New York, Michigan, Ontario, and 

 British Columbia. 



At all 5 locations, a treatment that had appeared in prelim- 

 inary tests to be about optimum for 'Mcintosh' was tested. It con- 

 sisted of liarvesting the apples at peak time for CA storage, quickly 

 cooling them to 38°F, and as quickly as possible sealing them in 

 CA where COo was brought to 12%. This 12% CO2 atmosphere was main- 

 tained for 2 weeks and then the apples were put under normal CA 

 conditions of 5% COo and 3% O2. The samples were kept in CA for up 

 to 8 months before Being compared with other CA samples that had 

 not received the 12% CO2 pretreatment. 



Besides conducting this test of what was believed to be about 

 the best treatment for 'Mcintosh* , each participant tested the 

 effects of 1 or more of the following factors that might influence 

 response to the CO2 treatment: harvest date; delaying treatment 

 after harvest; slow cooling during treatment; temperature, humid- 

 ity, and O2 level during treatment; increased CO2 concentration; 

 and, increased length of the CO2 treatment. 



