With strawberries, blueberries, raspberries, and blackberries now available locally, this is definitely berry season. Berries are always best eaten fresh, but it's often a good idea to freeze berries for use later in the year when they are no longer in season. Frozen berries go quite well in baked goods, smoothies, jams, or just partially thawed on ice cream. Berries tend to take well to freezing, relative to other fruits and vegetables, but there are steps you can take to further improve your results when freezing berries.

The problem with freezing berries, or any other food product, is the change in state from water molecules to ice crystals. As the product freezes, water molecules will expand as they turn into ice crystals. This expansion causes damage to surrounding molecules. When the product is thawed, the ice crystals contract back into water molecules, leaving a void where the ice crystal existed, and causing the berry to collapse in on itself and become mushy. This damage to molecules during freezing, and the mushiness associated with thawing are the two main factors associated with quality loss in frozen products. This will always be a problem when freezing food products, but the negative effects can be reduced if you can speed up the freezing process. The extent to which the water molecules expand in forming ice crystals is determined by how long it take them to freeze. The longer the freeze time, the larger the crystals. The shorter the freeze time, the smaller the crystals, and the smaller the negative effects. Frozen food companies understand this fact well, and generally flash freeze their products in a matter of seconds. Unfortunately, most of us at home do not have access to flash freezers, but we can still take measures to speed up the freezing process and improve our results when freezing berries at home.

Below are tips for the best results when freezing berries. Let us know if you have any tips or ideas from your own experiences.

1) Pick out any damaged berries. Damaged berries will not take well to freezing, they are best eaten right away, so they do not cause deterioration of other berries.

2) Wash berries gently (except blueberries). Be careful not to damage or oversaturate berries, but give them a gentle rinse to remove any dirt or impurities. Studies have shown that blueberry skins become tough when they are washed and then frozen, so it is generally recommended that blueberries not be washed prior to freezing - however, the extent to which the average consumer will notice tough blueberry skins is debatable.

3) Lay berries over paper towels and pat dry. Berries do not have to be bone dry, but should be relatively dry before freezing.

4) Hull strawberries (remove tops), and cut into halves or quarters. The idea here is to reduce the size of the strawberries, so that they will freeze faster.

5) Lay berries out on a baking pan, in a single layer. The single layer of berries will maximize surface area, and speed the freezing process, as will the metal baking pan which will quickly drop down to freezing temperatures.

6) Place tray of berries in the coldest part of the freezer. This will be the area closest to the cooling mechanism in your freezer, generally the back of the top shelf.

7) Remove berries from the freezer after they have frozen completely, 6-8 hours is usually plenty of time. Pack into ziploc bags and remove as much air as possible to reduce the potential for freezer burn. You can come close to a vacuum seal by placing a straw vertically in the bag, and sealing the bag up to the straw. Suck out any remaining air through the straw, then remove the straw, and quickly seal the remaining portion of the bag. Mark the current date on the bag.

*It's often a good idea to freeze berries in 1 cup quantities, so that you can thaw exactly what you need when prepping for baking applications.

Alex H. (Jun 10, 2012 at 1:55 pm)
If you've got lots of berries to freeze, it can be worth it to get some dry ice. There's an old Good Eats episode about it here. http://www.youtube.com/watch?v=TStJZ3yToO8

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