Carbon dioxide can reduce browning and increase shelf life in cut lettuce. One easy way to add CO2 is to exhale a small amount into the bag of lettuce, then seal it. For sanitary reasons, do this only with lettuce you plan to eat personally. Carbon dioxide is not beneficial for intact lettuce heads. This clever way to add carbon dioxide can increase your lettuce's lifespan by five extra days, in the best case scenario. Here's how to set it up:  Freeze 1 tsp (5mL) white vinegar in a spice jar or other small container. Pour 1 tsp (5mL) baking soda onto the frozen vinegar. Leave the lid off the jar, and cover with several layers of paper towel. Fasten with a rubber band. Keep this jar upright in a sealed container of lettuce. The vinegar will slowly melt and react with the baking soda to create CO2. If you have a vacuum-packing machine, you can use it on a jar of iceberg lettuce to keep it fresh for up to two weeks. Romaine lettuce typically lasts a week when vacuum sealed. This does not work well with butter lettuce and other tender leaves.  You can imitate a vacuum packing machine with a much cheaper (but less effective) hand pump. Punch a hole through the jar lid with a thumbtack, cover it with electrical tape, and pump air out through the tape.  This will not work with a plastic bag of lettuce, as the leaves will be crushed in the vacuum.
ازفري بداخل قطعة الخس الخاص بكِ. أضيفي مصدرًا أقوى من ثاني أكسيد الكربون. استخدمي جهاز تفريع الهواء لسحب الهواء من جرة الخس.