How to preserve lettuce

In this brief guide, we are going to answer the question “how to preserve lettuce” and discuss the different methods of preserving lettuce.

How to preserve lettuce

Lettuce can be preserved by :

  • Refrigerating
  • Freezing

Lettuce is a very common left green used in many salads. Lettuce is very susceptible to spoilage through wilting, bruising and yellowing.

The biggest share of the gross yield and area under crop (75%) is in China, India, and the USA. More than half of the global acreage falls on China (51.6%). During the study period, the country has seen an increase of 2% annually. In total, 14% of the sown area is accounted for by India, it is 9.1% in the USA (1).

How to clean lettuce for preservation

Lettuce grows close to the ground so there are a lot of contaminants such as soil, insects. Therefore, fresh lettuce must be properly cleaned and washed before storage. 

Fresh lettuce must be cleaned as soon as possible after purchase. There are also cleaned, packaged and pre-cut lettuce available in convenience stores. It is not necessary to wash packaged lettuce unless specified by the seller.

To clean lettuce :

  • Remove any yellow, wilted and bruised leaves. Mostly the outer leaves will be damaged, so remove those. Also, keep a lookout for insects hiding in between the layers of leaves. 
  • Wash the lettuce in cold running water. If you observe insects among the leaves, it is better to immerse the lettuce in cold water with a teaspoon of salt added. This will help to remove the insects.
  • Use a paper towel or a salad spinner to remove the water.

A study demonstrates that after washing, microbial populations of iceberg lettuce decreased significantly, when using tap water or water containing sanitizing agents. The use of aqueous chlorine dioxide at the applied dose (3 mg / L) was equally effective as sodium hypochlorite (100 mg / L) and it did not cause any detrimental effect on the sensory quality and the content of bioactive compounds of fresh-cut iceberg lettuce (2).

How to preserve lettuce by refrigerating

Storage temperatures directly affect fruit and vegetables metabolism. Storage at low temperatures usually prevents quality losses in chilling resistant plants. Usually the chlorophyll losses occur after 5 days, but wide oscillations can be observed. Lamb’s lettuce  dark stored at 4 or 10°C showed chlorophyll and carotenoids reduction after 8 days of storage (3).

Refrigerating is the easiest way to preserve lettuce. Cleaned lettuce can be refrigerated as follows:

  • Place the lettuce in a clean container or a plastic bag. 
  • You can refrigerate either the whole head of lettuce or individual leaves. 

The lettuce head can be wrapped in a damp paper towel. This provides enough moisture to prevent the leaves from wilting. If individual leaves are refrigerated, it is better to arrange the leaves in a container to prevent bruising.

  • Place the container or bag with the lettuce in the crisper drawer of the refrigerator.

Lettuce can also be washed in vinegar before refrigerating. A study showed significant reduction was observed in the mean E. coli count of artificially contaminated lettuce leaves after sanitization using 15 g L-1 acetic acid solution prepared with triple-strength vinegar (5).

To wash lettuce in vinegar solution :

  • Clean and remove the lettuce leaves from the head.
  • Place the lettuce leaves in a bowl.
  • Add one cup of vinegar to the bowl.
  • Add water to fill up the rest of the bowl.
  • Mix the lettuce leaves in the vinegar solution and let them soak for a few minutes.
  • Drain the solution, rinse and dry the lettuce leaves using a paper towel.
  • Place the lettuce leaves in an airtight bag and freeze them until needed.

Ethylene is a gas produced by certain fruits and vegetables as they ripen. Ethylene will cause the ethylene sensitive fruits and vegetables to ripen and rot prematurely.

Lettuce is sensitive to ethylene. It is important not to store ethylene producing fruits and vegetables such as apples, bananas, and tomatoes in the same refrigerator drawer as lettuce. Vegetables sensitive to ethylene, when exposed to ethylene concentrations above the sensitivity threshold, show russet spotting and yellowing (3).

How to preserve lettuce by freezing

Raw fruits and vegetables contain large quantities of water in proportion to their weight and, consequently, the water phase change occurring in freezing makes these products more susceptible to ice crystal formation and thawing than other types of food. Compared to ‘fresh’ vegetables and fruits, there are generally small differences in the mineral and fiber content of equivalent vegetables supplied as frozen (4).

Lettuce can also be preserved by freezing. Freezing preserves lettuce for longer than refrigerating. However frozen lettuce is more likely to wilt and lose its crispiness. This is caused by the formation of ice crystals within the plant cells which ruptures the cell walls. 

If you are planning to preserve lettuce for a dish where texture is important such as a salad, it is better to refrigerate the lettuce than freeze.

Lettuce can be either frozen as whole leaves or puree. More about freezing lettuce can be found here.

To freeze lettuce leaves:

  • Clean, wash and dry lettuce leaves using a paper towel.
  • Place the leaves in an airtight bag.
  • Freeze the leaves until needed.

Frozen whole lettuce leaves must be thawed in the refrigerator overnight before being used. Whole frozen leaves can be added to casseroles, quiches and can also be used as wraps.

To freeze lettuce puree :

  • Clean, wash and dry lettuce leaves using a paper towel.
  • Puree the lettuce leaves.
  • Pour the puree into a clean container or ice cube trays.
  • Freeze the puree until needed.

Frozen lettuce puree can be added to juices and smoothies.

Shelf-life of preserved lettuce

  • Refrigerating: If a whole head of lettuce is refrigerated, it will last for about 2 weeks. Individual lettuce leaves can be refrigerated for a maximum of 10 days (2).
  • Freezing: Frozen lettuce must be used within 6 months for the best flavor and quality.

How to freshen up wilted lettuce

Since lettuce is very susceptible to wilting and bruising, it is common to observe some wilting no matter the preservation technique. Slightly wilted lettuce can be easily freshened up by immersing in ice water for a few minutes. This will bring back crispiness to the leaves. When warm produce is cooled directly by chilled water, the process is known as hydrocooling.

Other FAQs about Lettuce that you may be interested in.

How long does lettuce last?

Can you eat brown lettuce?

Can bunnies eat iceberg lettuce?

Can you eat lettuce that has slugs on it?

Conclusion

In this brief guide, we answered the question “how to preserve lettuce” and discussed the different methods used to preserve lettuce. We also looked at the shelf-lives of lettuce preserved in different ways and how to freshen up wilted lettuce.

If you have any comments, please let us know.

References

  1. Shatilov, M. V., A. F. Razin, and M. I. Ivanova. Analysis of the world lettuce market. IOP Confer Ser Earth Environ Sci, 2019, 395. 
  2. López-Gálvez, Francisco, et al. Suitability of aqueous chlorine dioxide versus sodium hypochlorite as an effective sanitizer for preserving quality of fresh-cut lettuce while avoiding by-product formation. Posthar Biol Technol, 2010, 55, 53-60.
  3. Spinardi, Anna, and Antonio Ferrante. Effect of storage temperature on quality changes of minimally processed baby lettuce. J. Food Agric. Environ, 2012, 10, 38-42.  
  4. Evans, Judith A., ed. Frozen food science and technology. John Wiley & Sons, 2009 
  5. Souza, Giovanna C., Wilma A. Spinosa, and Tereza CRM Oliveira. Sanitizing action of triple-strength vinegar against Escherichia coli on lettuce. Horticultura Brasileira, 2018, 36, 414-418.