Some Experience with Use of A 

 l-lollow-fiber System for 

 CA-atmosphere Generation 



William J. Bramlage and Joseph E. Sincuk 



Department of Plant & Soil Sciences, University of Massachusetts 



Controlled atmosphere (CA) storage of apples 

 requires a method of reducing oxygen (Oj) concentra- 

 tion in the storage atmosphere from that of air (2 1%) to 

 the level desired for apple storage (usually 3% or less). 

 Originally, the process used fruit respiration to "pull 

 down" the O2, but at low storage temperatures this 

 reduction usually requires 14 to 21 days or more. We 

 now recognize that this length of time results in signifi- 

 cant loss of fruit quality, and recommend that the at- 

 mosphere be pulled down to 5% in no more than 3 days 

 after sealing the room. This reduction cannot be done 

 by fruit respiration alone. 



Rapid pull-down can be achieved by either displac- 

 ing most of the storage air with nitrogen (N2), as tank 

 gas or as liquid N2, or by using an external generator to 

 create a I0W-O2 atmosphere that is piped into the room. 

 Several types of generators were developed that mixed 



propane gas with air to produce carbon dioxide (CO2) 

 and water either by open-flame burning or by catalytic 

 chemical reaction. However, a series of storage explo- 

 sions have made both storage operators and generator 

 manufacturers wary about using these machines, and 

 they rapidly are becoming obsolete. 



In New England, many CA storage operators re- 

 cently have adopted use of liquid N, for CA pull-down, 

 a practice that we have advocated (Proc. 92"'' Annu. 

 Meet. Mass. Fruit Growers' Assoc. 1986:102-105), 

 because it requires little capital investment and 

 achieves a CA atmosphere rapidly and withoutbuildup 

 of CO2, which would have to be removed. Liquid Nj 

 also provides some cooling in the CA room. However, 

 use of liquid N2 is not problem-free. Some freezing of 

 fruit near the manifold outlets often occurs, and some 

 storage operators have difficulty obtaining timely de- 



Jt' «r I--- ... ^ 



> V i 



*■ / 



Mfi* H2* He, H^, CX)2, O?. Ar, CO. Ns, CH4 



pl^$t*' "Slow" 



'"' ' Relative Permation Rates 



Stream 





S , •> ijf^O j- / •.' X. V '-. AC ..> 



Figure 1. Relative permeation rates for the Prism Alpha™ hollow-fiber system. 



Fruit Notes, Summer, 1989 



