How to preserve vegetables in the freezer

In this brief guide, we are going to answer the question “how to preserve vegetables in the freezer”, and discuss the methods to preserve both raw and cooked vegetables in the freezer. We are also going to discuss the advantages and disadvantages of preserving vegetables in the freezer

How to preserve vegetables in the freezer

Vegetables are the largest food group consumed in the UK with an estimated total of 10.8 Mt sold annually. The market is worth £12.5 bn/yr and represents 16% of the total household expenditure on food (1). 

Both raw and cooked vegetables can be preserved by freezing at -18 °C in airtight containers or ziplock bags.

Freezing is one of the most efficient ways to preserve vegetables for long term storage.

Freezing preserves the flavor as well as the nutrient content of vegetables. However, especially the texture of cellular foods, like meat, vegetables and fruits, can be strongly impacted by the freezing process (2).

Freezing preserves vegetables by slowing down the growth of microorganisms that cause spoilage. However, it does not inactivate microbes or enzymes (2).

It is recommended to consume frozen vegetables within 8-12 months for the best flavor and texture (3).

How to preserve raw vegetables in the freezer

Vegetables such as tomatoes, bell peppers and onions can be frozen raw without blanching. 

Blanching is scalding the vegetables in water or steam for a short period of time. It is a very important step in freezing vegetables because it slows or stops the action of enzymes. If the enzyme action is not stopped before freezing, the vegetables may discolor, toughen or develop offcolors, so they may be unappetizing in a few weeks. Proper blanching also brightens color and helps  prevent loss of nutrients (3).

It is recommended to freeze cut-up vegetables separately in a tray and then transfer the frozen pieces into a ziplock bag. This allows the cut-up vegetables to freeze separately rather than in one big lump.

How to preserve cooked vegetables in the freezer

Certain vegetables must never be frozen raw. examples include starchy vegetables such as potatoes, sweet potatoes and yams. These vegetables must be either boiled, baked or blanched before freezing. Other examples are squash and beets (3). 

Always allow the cooked vegetables to cool down to room temperature before freezing.

Always allow the cooked vegetables to cool down to room temperature before freezing. Cooked vegetables usually cool down in about 30 minutes. As soon as pre- heating or cooking is completed, the vegetable is to be plunged into cold running water having a temperature of 50°F. After the vegetables have cooled down, freeze them as soon as possible.

The cooked vegetables must be stored in airtight containers or ziplock bags, labeled and then frozen.  The packaging requirements for most fruits and vegetables are very similar, the major prerequisite being that the package be moisture- vapor-proof (4). 

Dehydrated or canned vegetables can also be further preserved by freezing.

How to store vegetables in the freezer

It is crucial to follow proper storage procedures when freezing vegetables. The following methods will ensure that the frozen vegetables stay fresh for longer.

  • Vegetables must be stored in airtight containers or freezer-safe ziploc bags that minimize exposure to air during freezing. The containers or bags must always be labeled with the preparation date.
  • Wherever possible blanch the vegetables before freezing. Blanching deactivates the enzymes that cause a loss in flavor, color and nutrient content. 
  • If blanching is not possible, the vegetables can be treated with ascorbic acid (Vitamin C rich solution such as lemon juice) which would also reduce enzyme activity and discolouration. Enzymatic browning of vegetables and fruits is caused by the action of polyphenoloxidase (PPO), which catalyzes oxidation of phenolic compounds to the corresponding o-quinone in wounded tissues (5).
  • Maintain the freezer temperature at -18 °C or slightly below. Fluctuations in temperature will cause the food to spoil faster. If there are regular power outages or if the freezer doors are constantly being opened, the vegetables are at risk of being spoiled. Temperature fluctuations around the storage temperature also lead to ice crystal melting and regrowth (2).
  • Always store vegetables and fruits separated from fish and meat products to avoid the risk of cross-contamination. Separate meat and poultry from ready-to-eat foods (such as fruits, vegetables, cheeses, etc.) to avoid cross-contamination during your food preparation (6).
  • Store vegetables in vacuum packaging if possible. Vacuum packaging will create an oxygen-free environment that reduces the formation of ice crystals in the vegetables. Oxidation is the major cause of carotenoids degradation. Vacuum freeze-drying of biological materials is one of the best methods of water removal, with final products of highest quality (7).

How to use frozen vegetables

Frozen vegetables can be substituted for fresh vegetables in most recipes.

However, it is not advisable to use frozen vegetables in dishes where the texture is important such as salads.

Frozen vegetables can either be defrosted by placing them in cold water or thawed by keeping them in a refrigerator. Defrosted and thawed vegetables must not be refrozen. Vegetables thawed in the refrigerator can be left in the refrigerator for a couple of days before they are used whereas vegetables deforested in water must be used immediately.

Do not overcook vegetables. Cook only until tender. Most vegetables have been partially cooked when blanched, so less cooking time is required than for fresh vegetables. Cook in a small amount of water or use steam (3).

Advantages of preserving vegetables in the freezer 

  • Freezing is a quick and efficient way to preserve vegetables and can be done by anyone at home.
  • Frozen vegetables have a comparatively long shelf life.
  • Freezing preserves more nutrients compared to other methods of food preservation such as dehydrating and canning.
  • Freezing helps to reduce the wastage of vegetables by preserving the excess.

Disadvantages of preserving vegetables in the freezer

  • Frozen vegetables will not retain the same texture as fresh vegetables. Most frozen vegetables tend to become soft and mushy after they are thawed. This is caused by water expanding as it freezes and forming ice crystals which rupture the cell walls.
  • Certain vitamins such as vitamin B and C and antioxidants are lost during the freezing process. Frozen storage is effective in preserving ascorbic acid, but the blanching process prior to freezing often causes significant degradation in addition to leaching into the blanch water (8).
  • The flavor of frozen vegetables will deteriorate with time. 
  • The freezer temperature must be maintained without fluctuations and this consumes electricity. The vegetables may spoil if there are unavoidable power outages.
  • Vegetables may suffer freeze-burn. Loss of moisture causes brownish-white spots
  • on food known as freezer burn. Freezer burn actually does not spoil
  • the food but can cause toughness and often results in off-flavors (3).
  • Preparing vegetables prior freezing causes nutrient leaching (2).

Other FAQs about Vegetables that you may be interested in.

Can you eat raw vegetables?

Conclusion

In this brief guide, we answered the question “how to preserve vegetables in the freezer”, and discussed the methods to preserve both raw and cooked vegetables in the freezer. We also discussed the advantages and disadvantages of preserving vegetables in the freezer.

If you have any questions or comments, please let us know.

References

  1. Frankowska, Angelina, Harish Kumar Jeswani, and Adisa Azapagic. Environmental impacts of vegetables consumption in the UK. Sci Total Environ, 2019, 682, 80-105. 
  2. Van der Sman, R. G. M. Impact of processing factors on quality of frozen vegetables and fruits. Food Eng Rev, 2020, 12, 399-420.  
  3. Garden-Robinson, Julie. Freezing vegetables. 2021. North Dakota State University.
  4. Dawson, Elsie Halstrom, Gladys L. Gilpin, and Howard Reynolds. Procedures for home freezing of vegetables, fruits, and prepared foods: classified notes on review of literature. 1950.
  5. Chiabrando, V., And G. Giacalone. Effect Of Antibrowning Agents On Color And Related Enzymes In Fresh-Cut Apples During Cold Storage. J Food Process Preserv, 2011, 36, 133-140.
  6. USDA Recommends Adding Food Safety Items to Your Back-to-School List. 2022.
  7. Bhatta, Sagar, Tatjana Stevanovic Janezic, and Cristina Ratti. Freeze-drying of plant-based foods. Foods, 2020, 9, 87.
  8. Bouzari, Ali, Dirk Holstege, and Diane M. Barrett. Vitamin Retention in Eight Fruits and Vegetables: A Comparison of Refrigerated and Frozen Storage. J. Agric. Food Chem, 2015, 63, 957-962.