I eat frozen blueberries straight out of the freezer multiple times a day, and sometimes I buy a bag and the blueberries inside are frozen perfectly so that the core of the blueberry has crunchy ice crystals, and the outside doesn't, resulting in a massive burst of blueberry flavor. Can someone tell me how to freeze blueberries this way myself? I'm pretty sure this isn't a common question so please don't be afraid to post an answer that you aren't sure is correct, because this is top of the line blueberry science that is very experimental, and i'm willing to try multiple freezing techniques to get the perfect result.
Fruit – How to freeze blueberries so that there are ice crystals inside
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Best Answer
Normally freezing processes try to avoid forming large ice crystals by freezing rapidly and maintaining a temperature well below the freezing point of the liquid in the product (not simply 0°C due to sugar and other solutes, which concentrate as some liquid freezes).
I suspect that the ones you are aiming to imitate have been through a thermal cycle in transit -- quite possibly as you take them home.
So you can try to do the opposite. Freeze fresh blueberries at home, in a single layer but fairly slowly (perhaps freezing them in an isulated container and/or adding large containers of room temperature water to the freezer at the same time). Allow to nearly defrost and freeze again. If you're starting from frozen berries, allow them to nearly defrost and then refreeze slowly.
You'll have to be careful about the quality of other things in your freezer doing this, and the goal is to stay cold enough that food safety isn't an issue, or at least no more of an issue than keeping fresh berries in the fridge for a few days before freezing. As a result I leave the mechanics at an exercise for you. A cool box with a thermometer inside may be useful.