Food preservation experts recommend that beans should not be frozen without blanching. Unblanched, beans lose nutrients, flavor and color once thawed. Blanching stops the enzymes in vegetables from working and is necessary for preservation.
Enzymes cause vegetables to ripen, something that must be suspended for vegetable preservation. Freezing beans without blanching first merely slows the enzymes down instead of stopping them, resulting in mushy, flavorless food. Blanching also has the added benefit of killing any bacteria or germs on the beans, brightening the colors and softening up the vegetables.
Blanching times vary depending on the type of vegetable. For instance, beans require only three minutes while greens such as Brussels sprouts take up to five minutes, and artichoke hearts require six minutes. Blanching for the correct time is important, as over-blanching can draw out the nutrients and flavor and under-blanching only stimulates instead of stops the enzymes.
Blanch beans either through water blanching. To water blanch beans, heat water until it boils, and add the beans. Once the water starts boiling again, keep the beans in for three minutes, and remove them. Cool the beans in ice water before removing all excess water and placing them freezer-safe bags.