Whether you are wanting to freeze a surplus of summer squash or simply prepare squash for a super quick stir-fry, blanching is a crucial step to help maintain the texture of the squash when cooking it later. A two-part process, blanching is especially important prior to freezing to destroy the enzymes that, if frozen raw, would cause the squash to break down and lose both nutrients and structure.
Cut squash into pieces depending on how you plan to use it, such as 1/2-inch-thick disks to use in stir-fries, diced to use in soups or sauces, or horizontally in half then lengthwise into eighths to bake in a gratin.
Fill a large 8- to 12-quart pot with water up to three inches from the brim. Have a large bowl filled with ice and water standing by the stove. Bring water in the pot to a rolling boil over high heat.
Slide the squash from the cutting board into the boiling water using your knife, and let the water come back up to a boil. Start a timer for three minutes as soon as the squash hits the water and then boil for two to three minutes, depending on the size of the pieces. Check it after the first two minutes; the squash should be slightly crunchy but not raw in the middle. When it's done, immediately remove the squash from the boiling water using tongs, a metal strainer, or a wide perforated ladle and plunge it into the ice water to chill it down quickly. Drain well in a colander before cooking or freezing.
Do not be tempted to skip the ice water bath; this is vital for discontinuing the cooking process. If this step is skipped, the squash will become very soggy or even disintegrate.