Freezing is the best way to preserve broccoli. It doesn't dehydrate well, and it loses nutrients and gets mushy if you pressure can it.
Giving the broccoli florets and stems a quick blanching in boiling water before freezing them ensures that they will retain a good texture when you get around to cooking with them.
The single layer initial freeze prevents the broccoli pieces from clumping together. The fact that they stay loose is a big advantage when, for example, you have a quart container of frozen broccoli but only need to take out a cup of it for a recipe.
Here are the easy steps for freezing broccoli:
Clean and Cut into Florets
Soak the whole broccoli in water for a few minutes in water to get rid of any dirt or garden bugs. Drain. Cut off the thick stem and set it aside. Use a paring knife to separate the florets into pieces no more than 1 1/2-inches thick.
Prepare the Broccoli Stems
Broccoli stems are arguably even more delicious than the florets and too often discarded. However, if you leave the thick skins on the stems they take longer to cook than the florets. The solution is to peel them with a vegetable peeler.
Cut off the tough bottom 1/2-inch or so of the stems and compost or discard. Peel the rest. Chop into 1/2-inch thick pieces.
While you are preparing the broccoli, have a pot of water coming to a boil on the stove. Also get a big bowl of ice water ready.
Blanch the Broccoli
Once you have separated the broccoli into florets and peeled and chopped the stems, drop the broccoli pieces into the pot of rapidly boiling water.
Let them cook for 2 minutes. Drain the broccoli in a colander. Alternatively, you can steam the broccoli for 2 minutes rather than boiling it.
Chill the Broccoli
Immediately transfer the blanched broccoli to the bowl of ice water. This stops the residual heat in the vegetables from continuing to cook them.
Leave the broccoli in the ice water for 3 minutes. Transfer the broccoli to a colander and leave it to drain well for a few minutes.
Single Layer Freeze
Spread the blanched and chilled broccoli in a single layer on a baking sheet. Freeze for 1 - 2 hours.
It is not necessary to thaw frozen broccoli before cooking it. Subtract the 2 minutes the broccoli was blanched from the cooking time when you cook your frozen broccoli.