Have you seen Pinterest posts about storing lettuce in a jar to keep it fresh? One post claims lettuce in a jar will never go brown! Will storing lettuce in a jar really extend its shelf life? Is it safe?
For insight on this topic, we reached out to Dr. Julie Albrecht, Professor, Extension Food Specialist, University of Nebraska-Lincoln.
Are there any safety issues with storing lettuce in a jar?
Julie A. Albrecht, PhD, RD: The packaging that produce comes in (plastic bags, plastic containers, etc.) does have some gas permeability (allowing gas to pass through). Produce – lettuce, tomatoes, carrots – are living things, even though they are picked from the plant. These products will naturally continue to grow, mature and eventually die/spoil. These products respire (inhale and exhale), just like you and me. For example, if we put bananas in a bag, they will ripen faster (and spoil faster) because the bag fills up with ethylene gas produced by the banana, which accelerates ripening. When you leave bananas on the counter, they do not ripen as fast, because the ethylene gas is not allowed to build up around the bananas.
If the jar has a lid on it, the produce is using up the air – usually the oxygen – and giving off (respiring) other gases. Salad ingredients – lettuce, cucumbers, tomatoes – all grow near the ground. Clostridium botulinum spores can be present on these products. When the oxygen is used up, it can cause an ideal environment, especially if temperature abuse (improper storage temperature) occurs, for the spores to form into live cells and produce the deadly toxin. Bacteria can grow in the presence of nitrogen (not oxygen). Note: We breathe in air, but only use the oxygen and breathe out the remaining gases.
Are there any ways you should prepare the lettuce before putting it in a jar?
Julie A. Albrecht, PhD, RD: Washing produce is always recommended but the added water provides more water for bacteria and mold (oxygen is needed for mold) to grow.
Would it be dangerous to vacuum pack these?
Julie A. Albrecht, PhD, RD: Absolutely - it would be dangerous. Just like keeping the lid on the jar, removing oxygen (vacuum packaging) would give the right environment, especially if temperature abuse (improper storage temperature) occurs, for the spores to form into live cells and produce a deadly toxin.
What about shelf life?
Julie A. Albrecht, PhD, RD: I would guess that the bottom ingredients in the jar may get mushy more quickly, especially if they have been washed properly and the extra water is present.
What do I need to know to keep foods, including salad ingredients, safe?