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How to blanch vegetables before preserving

Quick facts

  • Fresh vegetables should be blanched before freezing, drying or dehydrating.   
  • Blanch vegetables by adding them to boiling water or by exposing them to steam for a very short period of time, and then cooling quickly.
  • Blanching is an important step in preserving vegetables for both food safety and quality.

Food safety and quality

Before preserving vegetables, blanch the vegetables to improve the safety and quality of the final product. All vegetables should be blanched and quickly cooled before freezing, drying or dehydrating. Exceptions: Diced or cut onions, green onions, leeks and peppers do not need to be blanched before preserving. Some pressure canning recipes also require vegetables to be blanched.

Freezing, drying and dehydrating do not kill any bacteria that may be present on the vegetables. Bacteria need moisture (water) and an ideal temperature to grow. Drying and dehydrating remove moisture from the vegetables. This temporarily stops bacteria growth. When moisture or water is added back to the dried vegetables, bacteria can begin to grow again. Freezing also temporarily stops bacteria growth. However, as the frozen vegetables are thawed, bacteria can begin to grow, especially if the vegetables are not properly thawed.     

Blanching the vegetables before preserving improves food safety by killing bacteria that might be on the vegetables. Many bacteria are sensitive to heat. This means the bacteria are destroyed when exposed to high temperatures, like the temperature of the boiling water or steam used for blanching vegetables. 

The quality of frozen and dried vegetables are also improved when the vegetables are blanched before preserving. Fresh vegetables contain enzymes that impact the freshness, color and flavor of the vegetables. Blanching deactivates these enzymes so the peak quality is preserved. 

Unfortunately, if vegetables are not blanched correctly, the vegetables can become too soft and essential nutrients, like vitamin C, can be lost. The high temperature of boiling water or steam weakens the cell walls and the vegetables lose their crunchy texture. For some vegetables, especially cut vegetables, steam blanching limits the nutrient loss compared to blanching in boiling water. Blanch vegetables at their peak ripeness and follow the recommendations below to avoid an undesirable texture and maintain good nutritional content. 

How to blanch vegetables

The general ratio is to use one gallon of water for every one pound of vegetables, except leafy green vegetables. Use two gallons of water for every one pound of leafy greens because raw leafy greens take up more space. 

Underblanching, or not exposing the raw vegetables to boiling water or steam for a long enough time can negatively impact the quality of the preserved vegetables. As the vegetables heat up during the blanching process, the enzymes begin to increase their activity before being deactivated by the high temperature. If the vegetables are not properly blanched, the enzymes will continue their activity even after cooling. This can lead to off taste and texture of the vegetables. 

Overblanching, or exposing the raw vegetables to boiling water or steam for longer than the recommended times can lead to very soft or mushy vegetables which may not preserve well. Also, overblanching of vegetables can increase the loss of essential nutrients. 

Before blanching the vegetables, always thoroughly wash vegetables then peel and cut the vegetables as desired. Use safe food handling practices to prevent cross-contamination before blanching. 

Blanching methods

There are two methods for blanching vegetables, boiling water or steam. Blanching can take between 1 and 15 minutes at a temperature of 160 to 212 degrees Fahrenheit. Using a microwave to blanch vegetables before preserving is not recommended by the National Center for Home Food Preservation because it can cause uneven blanching. 

Boiling water

Boil the water in a pot large enough to hold the vegetables and that can be covered with a lid. Once the water is boiling, add the vegetables, stir and cover the pot. The vegetables can be added directly into the water or a wire basket can be used. The water should return to boiling within 1 minute. If the water does not return to boiling within 1 minute, the ratio of water to vegetables may be wrong. 

Once the water returns to boiling, start the timer and blanch according to the recommended time. Remove the vegetables from the boiling water after the recommended time and cool quickly. Replace the water for each batch to prevent cross-contamination. 


Fill a pot with enough water to steam the vegetables without running dry. Use a wire basket or perforated metal strainer to hold the vegetables. Place the vegetables in a single layer to allow the steam to reach all of the vegetable surfaces for even blanching. 

Once the water is boiling, place the vegetables in the pot. The vegetables should be at least 3 inches above the water. The vegetables should not be touching the water. Cover the pot and start the timer. Blanch the vegetables according to the recommended time. Remove the vegetables from the pot and cool quickly. 

Recommended blanching times

The recommended times are based on research and testing. It is important to note that steam blanching can take 1 ½ times longer than blanching in boiling water.

Vegetable blanching times (water blanching)

Vegetable Blanching In boiling water (minutes) Blanching in steam (minutes)
Artichoke - Globe Hearts 7 11
Artichoke - Jerusalem 3-5 5-8
Asparagus Small stalk 2 3
Asparagus Medium stalk 3 5
Asparagus Large stalk 4 6
Beans - snap, green or wax 3 5
Beans - lima, butter or pinto Small 2 3
Beans - lima, butter or pinto Medium 3 5
Beans - lima, butter or pinto Large 4 6
Broccoli - flowerets 1 1/2 inches across 3 5
Brussels sprouts Small heads 3 5
Brussels sprouts Medium heads 4 6
Brussels sprouts Large heads 5 7
Cabbage or Chinese cabbage Shredded 1 1/2 2 1/2
Carrots Small, whole 5 8
Carrots Diced, sliced or strips 2 3
Cauliflower - flowerets 1 inch 3 5
Celery 3 -
Corn - corn-on-the-cob Small ears (cooling time is twice the time of blanching) 7 10
Corn - corn-on-the-cob Medium ears (cooling time is twice the time of blanching) 9 13
Corn - corn-on-the-cob Large ears (cooling time is twice the time of blanching) 11 16
Corn - whole kernel or cream style Ears blanched before cutting corn from cob. (cooling time is twice the time of blanching) 4 6
Eggplant 4 6
Greens - collards 3 5
Greens - all other 2 3
Kohlrabi Whole 3 -
Kohlrabi Cubes 1 -
Mushrooms Whole (pretreat soak 5 min. in anti-darkening solution: 1 tsp. of lemon juice or 1 ½ tsp. of citric acid to a pint of water.) - 5
Mushrooms Buttons or quarters (pretreat soak 5 min. in anti-darkening solution: 1 tsp. of lemon juice or 1 ½ tsp. of citric acid to a pint of water.) - 3 1/2
Mushrooms Slices (pretreat soak 5 min. in anti-darkening solution: 1 tsp. of lemon juice or 1 ½ tsp. of citric acid to a pint of water.) - 3
Okra Small pods 3 5
Okra Large pods 4 8
Onions (blanch until center heated) 3-7 -
Onions Rings 10-15 seconds -
Peas - edible pod 2-3 4-5
Peas - green 1 1/2 - 2 1/2 3-5
Peppers - sweet Halves 3 5
Peppers - sweet Strips or rings 2 3
Potatoes - Irish (new) 3-5 5-8
Rutabagas 3 5
Soybeans - green 5 -
Squash - chayote 2 4-5
Squash - summer 3 5
Turnips or parsnips 1/2 inch cubes 3 5

Fully cook beets, pumpkin, sweet potatoes, and winter squash prior to freezing. Add tomatoes to boiling water for 30-60 seconds, cool and remove skin.

Cooling vegetables

Immediately after blanching, cool the vegetables to prevent further cooking and a mushy texture. To cool the vegetables, rinse under cold running water, or dunk into a cold water or ice-water bath. Swirl or stir the vegetables to heat transfer the heat from the vegetables to the water. This process should take no more than a few minutes. Do not let the blanched vegetables sit or soak in the cold water as this can impact the texture of the final product. Drain the vegetables and place in a single layer on a perforated tray, or on a tray lined with paper towels. If you choose to use cloth towels, ensure the towels are clean and have not been used to dry any surfaces or hands as this could cause cross-contamination. Let the vegetables completely air dry before preserving.   

Recipes and resources

Learn how to freeze sweet corn and leafy greens in our food preservation section. For more recipes, visit the National Center for Home Food Preservation

Learn more about drying food at home.

Amy Johnston, Extension educator

Reviewed in 2023

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