Blanching Is Essential When Freezing Vegetables

Posted: August 4, 2012

Freezing is a quick way to preserve vegetables so we can enjoy them all year round. To ensure your frozen vegetables will be a high quality product, blanch them before freezing...

According to Cathy Guffey, Penn State Extension educator in Bradford County, blanching stops the action of enzymes that naturally occur in vegetables to help them grow and ripen. The enzymes continue to act after harvest and will cause color, flavor, texture, and nutrient losses.

Freezing slows down the action of enzymes but does not stop them.  Blanching also removes air and helps vegetables to shrink so they take up less freezer space. It reduces plant and pesticide residues and microorganisms on vegetable surfaces. In addition, blanching helps to loosen peels that need removing and brightens the color of vegetables. 

A pan of boiling water is the best way to blanch vegetables. Steam blanching works well for broccoli, pumpkin, sweet potatoes, and winter squash. Microwave blanching is not recommended. 

Mrs. Guffey says it is important to follow blanching directions precisely. Timing is crucial. Over blanching will cause vegetables to start cooking and quality will be lost. Under blanching will stimulate enzyme activity and is actually worse than not blanching at all. 

There is no "one time fits all" for blanching. Time will vary depending on the vegetable and its size. Blanching times and steps for water and steam blanching can be found at 

Mrs. Guffey offers these additional tips for success in blanching: 

     * Use a blancher that has a basket that fits inside and cover; or fit a wire basket into a large pot with a lid.

     * Use one gallon water per pound of vegetables when water blanching.

     * Blanch vegetables in small batches. After adding vegetables to the boiling water and putting the lid on the pot, the water should return to a boil in about one minute. If it doesn't, you are using too many vegetable pieces for the amount of boiling water.

     * For water blanching start counting blanching time as soon as water returns to a boil. For steam blanching begin counting time as soon as the lid is on pot.

     * Cool blanched vegetables quickly to stop cooking. Plunge the basket into very cold water and change the water frequently, or use ice water. If ice is used to cool, you will need about one pound of ice per pound of vegetables.

     * Vegetables should be cool enough in about the same amount of time they were blanched.

     * Drain vegetables well after cooling since extra moisture can cause loss of quality when the vegetables are frozen.

     * Once cooled and drained, quickly move the vegetables to freezer containers and put them into the freezer.

     * As with many "rules" there is often an exception. It's okay to freeze onions, sweet and hot peppers, and raw tomatoes without blanching. 

Visit the Penn State Food Preservation web site at for more information or for home food preservation recipes.

Karen Thomas is a family and consumer sciences educator for Penn State Extension in Lackawanna County.