If your garden has produced a bumper crop of yellow summer squash, don't panic. Summer squash can easily be frozen, and will taste delicious in soups, stews and casseroles. Blanching is an all-important step when freezing summer squash because it will stop the enzyme action in the vegetable and preserve the fresh flavor.
Start with fresh, firm squash with clear, bright skin. Don't blanch squash that is bruised, soft, or off-color. Summer squash is perishable, so if you aren't ready to blanch it immediately, put it in the refrigerator and blanch it as soon as possible..
Wash the squash in lukewarm water. Rubbing the squash gently with your fingers should be enough to remove dirt, but if necessary, you can use a soft vegetable brush.
Fill a large saucepan about 2/3 full of water and bring it to a full boil. While the water is coming to a boil, fill a large bowl with ice and set it aside.
Put the squash on a cutting board and slice it into 1/4-inch slices. Work quickly, and don't let the squash sit out for more than 30 minutes, or it will begin to soften and turn brown. Slice one batch at a time.
Put the squash slices in the boiling water and put a lid on the saucepan. User a timer and boil the squash for exactly three minutes.
Use a slotted spoon to remove the squash from the boiling water, and put it in the bowl of ice. Add more ice if necessary to stop the squash from overcooking. The squash is now ready to freeze. The water can be returned to a boil and used to blanch additional batches.