Controlled Atmosphere Storage of Fruits and Vegetables, Second ...

32 Chapter 3Passive scrubbingThe simplest method is to place bags or palletsof a CO 2-absorbing chemical (usuallycalcium hydroxide (Ca(OH) 2) inside the store,which can keep CO 2levels low (usually about1%). This method is referred to as ‘productgenerated’, since the gas levels are producedby the crops’ respiration. Ca(OH) 2reacts irreversiblewith CO 2to produce calcium carbonate(CaCO 3), water and heat.For greater control, the bags or palletsof lime may be placed in a separate airtightroom. When the CO 2level in the store is abovethat which is required, a fan draws the storeatmosphere through the room containing thebags of lime (Fig. 3.3) until the required levelis reached. After scrubbing the air shouldre-enter the store just before it passes over thecooling coils of the refrigeration unit. Theremay also be some dehydration of the air as it isFig. 3.3. A simple lime scrubber for CO 2used inmany traditional controlled atmosphere stores in theUK. (Photograph courtesy of Dr R.O. Sharples.)passed through the lime, and the air may needhumidification before being reintroduced tothe store. The amount of lime requireddepends on the type and variety of the cropand the storage temperature. For example,Koelet (1992) stated that for 1 t of apple fruit7.5 kg of high-calcium lime is needed every6–10 weeks for most cultivars. Bishop (1996)also calculated the amount of lime required toabsorb CO 2from CA stores on a theoreticalbasis. He calculated that 1 kg of lime willadsorb 0.59 kg of CO 2, but for a practicalcapacity he estimated 0.4 kg of CO 2per 1 kg oflime. On that basis the requirement of limefor Cox’s Orange Pippin apples stored in