how to keep lettuce crisp

{"cid":"91191364","title":"Lettuce \/ Potato Chip Slicer Machine 220 \/ 380V Voltage 70KG Net Weight","imgUrl":"https:\/\/img.silkroadsl.com\/nimg\/f5\/19\/924f24fc006793b1c8aa89c38b8a-200x200-1.jpg","attrs":{"Price":"Negotiable","Brand Name":"XUANHUA","Model Number":"QC-300","Minimum Order Quantity":"1","Delivery Time":"5-20 working days after received payment","Certification":"CE","Place of Origin":"CHINA","Payment Terms":"L\/C, T\/T, Western Union","Supply Ability":"200 sets\/month","Packaging Details":"Wooden Packing or according to your requirements","Product Name":"Fruit and vegetable cutting machine","Finished Product":"Slices, Chipps, Cubes","Stick Blade":"1~13 mm","Slice Blade":"3*3~12*12mm","Cube Blade":"0.87m2","Capacity":"300~600 Kg\/h"}}