Freezing is a great way to preserve foods. But when it comes to vegetables, there is more to freezing than putting foods directly into the freezer because this does not destroy harmful pathogens that cause spoilage. When foods are frozen, their enzyme action is slowed, but not stopped. One solution to this problem is blanching vegetables before you freeze them. Blanching stops food's enzyme action and reduces your risk of food poisoning.
Note: Blanching is great for vegetables, but for other foods such as meat, see our freezer storage chart or download the Is My Food Safe? app.
What Is Blanching?
Blanching is a process where vegetables are exposed to boiling water or steam for a brief period and then rapidly placed in ice water to prevent cooking. Blanching stops the food's enzyme action and destroys any microorganisms present on the vegetables surface reducing your risk of food poisoning.
It is important to follow the recommended times for blanching each vegetable because overbalancing results in cooked produce with a loss of flavor, color and nutrients, and under-blanching can cause the enzymes to continue ripening the food. Check out the blanching chart below for proper blanching times.
Here are a few reasons to blanch vegetables:
- Blanching stops enzyme actions which can cause loss of flavor, color and texture.
- Blanching brightens the color and helps slow the loss of vitamins.
- Blanching cleanses the surface of dirt and organisms.
- Blanching wilts or softens vegetables and makes them easier to pack.
How To Blanch?
Blanching can be completed using boiling water, steam or a microwave oven:
- Boiling Water: Use one gallon of water per one pound of vegetables and two gallons for leafy greens. Place vegetables in a wire basket, lower into boiling water and then cover. Keep in mind water should return to boiling within one minute or you are using too little water. As soon as water returns to a boil, start counting blanching time based on the chart below.
- Steam: Place a layer of vegetables in a wire basket, suspend in steamer above rapidly boiling water and then cover. As soon as covered, start counting blanching time. Steaming takes about one and a half times longer than blanching.
- Microwave: Research has shown that microwave blanching may not be effective because some enzymes may not be inactivated. If you choose to use the microwave method, use small quantities of vegetables and follow directions given by microwave manufacturer.
Cooling: Vegetables should be cooled quickly and thoroughly to stop the cooking process immediately after blanching. Plunge the vegetables into a large bowl of cold water (60ºF or below). Change water frequently or use cold running water or ice water. If you use ice, you need one pound of ice for each pound of vegetable. It should take the same amount of time to cool vegetables as it did to blanch them. Drain vegetables thoroughly after cooling because extra moisture can reduce quality when vegetables are frozen.
See blanching times for various vegetables from The University of Georgia Extension