According to About.com, freezing is the best way to preserve cauliflower. While there are other ways to preserve cauliflower, freezing it helps retain nutrients and prevent mushiness.
Before storing cauliflower in the freezer, it needs to be prepped, blanched and properly sealed. Thoroughly clean the cauliflower in warm water before removing any green parts of the vegetable. Separate the cauliflower into smaller pieces, and then place the cauliflower pieces in boiling water and cook for 5 minutes. Remove the pieces and place them in a bowl of ice water for 3 minutes. Drain the cauliflower pieces, and place them on a lined baking tray. Freeze the pieces for a few hours on the tray before transferring them to freezer bags or freezer-safe containers and placing them back in the freezer.