Pumpkin and other winter squashes will keep for months if stored properly (see below for the best way to store them). But sometimes it is advantageous to freeze or can them so that they are easier to use later on.
Note that although winter squash puree freezes beautifully, it cannot be safely canned at home. Pureed winter squash is too dense for even the extreme heat of pressure canning to penetrate completely. Small chunks or cubes of butternut or other winter squashes may be immersed in liquid and pressure canned.
Winter squash also dehydrates well.
Here are the details on the three best methods for preserving pumpkin, butternut and other winter squashes.
Storing Whole Winter Squash
Left unpeeled, whole winter squash can keep at room temperature for at least 3 months. However, sometimes spots of mold occur that soften the outer layer and ultimately spoil the squash.
To prevent mold spots, commercial growers sometimes wax the outsides of winter squashes. If you are going to store unwaxed winter squashes, you can achieve the same effect by oil buffing them.
To oil buff winter squashes, first wash them thoroughly to remove any dirt. Dry them completely (it is important that the surface of the squash be completely dry to prevent mold). Put a small amount of vegetable oil on a paper or clean cloth towel. Rub the oil all over the surface of the squash, buffing off any excess oil. The squash should be just barely shiny and not greasy to the touch.
Be sure to work the oil into the crevices of scallop-shaped squashes such as acorn and delicata varieties.
Freezing Winter Squash
Cooked and frozen pumpkin and butternut squash purees are ready to use in pies, soups, muffins and other dishes. This is one of my favorites ways to preserve winter squash.
If you've ever tried to make pumpkin pie from scratch and been disappointed in the watery results, here are two tips that will ensure your homemade version is even better than the stuff out of a can: 1. roast the pumpkin rather than boiling or steaming it, and 2. seek out varieties of pumpkin that are specifically meant to be used for pie. These have been bred to have a lower water content.
To freeze pumpkin or other winter squash, first cut the squash in half and scoop out the seeds. Place the squash halves cut side down in a baking dish and pour in 1/2-inch of water.
Bake in a 400F oven until the flesh of the squash is completely cooked (the peels will be starting to show a few brown spots). This will take 40 minutes to 1 hour.
Let the squash cool for 10 minutes. Scoop out the cooked flesh with a spoon.
At this point you can freeze the cooked squash as is. But I find it more useful to puree it first, either in the food processor or by mashing thoroughly with a potato masher. Pureeing the squash first gives me a ready-to-use product later on. Do not add liquid when you puree the pulp (we're trying to avoid that watery pie, remember?).
Pack the cooked squash into freezer bags and store the bags horizontally for the most efficient use of freezer space. Alternatively, pack the squash into upright freezer containers leaving 1-inch head space. Either way, measure the squash before freezing it and label clearly with the amount. This will make your life much easier when it comes time to cook with it.
Dehydrating Winter Squash
Dehydrated pumpkin and other winter squash works well for soups. I find it less successful for pies and other recipes.
The advantages of using this preservation method are the light weight and little storage space required, plus the final product will keep indefinitely if stored away from direct light and heat.
Bring a large pot of water to a boil. Peel and seed the squash. Cut into pieces 1/4-inch thick and 1 to 2 inches long.
Blanch the squash in the boiling water for 3 minutes. Drain. Spread on dehydrator trays leaving space between the pieces so that air can circulate around them.
Dry at 125F until brittle. Store in airtight containers away from direct light or heat.
To use, pour boiling hot water over the dehydrated squash pieces and let steep for 15 minutes before draining and proceeding with your recipe (save the soaking liquid to use in soups).
Two important food safety notes: 1. You must pressure can pumpkin and other winter squash. Boiling water bath canning is not a safe method for unsweetened, unpickled squash. 2. It is not safe to home-can pureed pumpkin and winter squash because of their density. You need to do chunks.
Bring a large pot of water to a boil. Peel and seed the squash. Cut into 1-inch chunks. Blanch the squash chunks in the boiling water for 2 minutes.
Remove the blanched squash with a slotted spoon and transfer to clean pint or quart canning jars (it is not necessary to sterilize the jars for this recipe).
Add 2 teaspoons per pint or 1 tablespoon per quart of lemon juice to each jar. Pour the blanching liquid over the squash and lemon juice. The squash should be be completely immersed in the liquid, but there should still be 1/2-inch head space in each jar.
Screw on canning lids. Pressure can at 10 pounds pressure, 55 minutes for pint jars, 90 minutes for quarts (adjust the times if necessary for high altitude canning).