Berries can be frozen with or without sugar. To freeze whole berries without sugar, wash, cap and drain the berries. Tray freezing will prevent the berries from sticking together. Spread them in a single layer on a baking sheet or jelly roll pan and freeze until solid—an hour or two. Then transfer them to plastic freezer bags pressing out as much air as possible. The expansion of frozen water in the berry will rupture its cell walls causing the berry to soften when thawed. Therefore, they taste best when eaten in a slightly thawed state with a few ice crystals remaining.
To freeze whole, sliced or crushed strawberries in sugar, add ¾ cup sugar to 1 quart (about 1⅓ pounds) strawberries. Stir until most of the sugar is dissolved and let stand for 15 minutes before putting into containers. Soft sliced berries will yield sufficient syrup for covering if the fruit is layered with sugar and allowed to stand 15 minutes. Allow adequate headspace so that syrup does not expand and overflow the container when the berries freeze. Allow ½ inch headspace for berries packed without added sugar or liquid. Allow 1 inch headspace in wide top containers (¾ inch in narrow top pints and 1½ inches in narrow top quarts) when packing in juice, sugar, syrup or water, or the fruit is crushed or pureed.
Artificial sweeteners may be used to freeze berries, but they do not provide the beneficial effects of sugar such as color protection and thickness of syrup. Use the manufacturer’s directions to determine the amount of artificial sweetener to use. Artificial sweeteners can also be added after the berries are thawed.
The more quickly berries freeze, the higher their quality will be and the smaller the ice crystals will be. The desirable temperature for storing frozen foods is 0°F or lower. To facilitate more rapid freezing, set the temperature control at minus 10°F or lower about 24 hours in advance. Place packages in contact with the freezer surfaces in the coldest part of the freezer. Allow a little space between packages so air can circulate freely until the berries are frozen; then store the packages close together. Never freeze more than 2 pounds of berries per cubic foot of freezer space.
Frozen strawberries can be used to make jam, but some planning ahead will yield the best results. Unsweetened berries work well because all you need to do is thaw the fruit completely before crushing and measure as usual. Do not drain off excess juice. If you sweeten the berries to freeze them, record the amount of sugar added because the amount of sugar in the fruit must be subtracted from the total amount of sugar in the jam recipe. The method of combining ingredients when using liquid and powdered pectin differs. Therefore, when using pre-sweetened berries, you will need to use liquid pectin to make cooked jam in order to have the jam set properly. This is not a problem when making freezer or no-cook jams. Slightly under-ripe fruit contains more natural pectin than ripe fruit. Freezing a combination of ripe and slightly under-ripe berries—about ¾ fully ripe and ¼ slightly under-ripe —will provide the best mixture for jam.
Look for more preservation recipes for strawberries and other berries are on the Penn State Food Preservation web site.