what's a good technique for freezing blueberries?

Lay them out on a tray in a single layer and freeze them flat first. Once they're frozen, pour the frozen berries into a freezer bag and store them that way. This has worked well for me.

Lay them out on a paper towel overnight so that the skins dry completely. This gives the benefit of keeping the frozen blueberries from sticking together without needing lots of freezer space to do a quick freeze individually on a sheet pan. Then bag in a freezer bag and freeze.

Note that whenever you freeze fruit, the liquid will burst the cell walls as it thaws, causing the resulting berry to be mushier. In my experience, frozen blueberries aren't good for eating alone. To bake with blueberries, thaw them by placing them in a mesh sieve or collander and running water over them until the water is clear off the bottom (no pigmentation from the skins, which may color your baked goods) and the berries are thawed. Dry the skins before using in baking.

Using these techniques I have not once had any of the 30 pounds of blueberries I froze this summer burst in the freezer and have successfully made many blueberry baked goods from the results.

As fast as possible, as it minimizes ice crystal growth (which breaks the cell walls, and causes the mush problem).

As most of us don't have access to liquid nitrogen, I'd probably try cooling them down in the fridge first, then freeze them with dry ice, crushed. See the transcript from Good Eats : Strawberry Sky, where Alton Brown used dry ice on Strawberries.

We have a friend who runs a fruit stand, so we get a lot of blueberries every year. I've never thought of trying to keep them from getting mushy, I just take it for granted that the frozen ones are better used for making blueberry pie or crisp, sauce, or jam.

That said, I think the bigger berries don't seem to burst as much. I wash all my berries to get rid of all the stems or squished ones, then dry them and spread them out into a single layer on cookie sheets to freeze. I know that when I've pulled out some of the bigger berries from the freezer, they seem to be intact. Maybe the skin is a bit more resilient when they've ripened that much?

Remove any leaves, stems, or blemished berries. Do not wash the berries, as that will result in a tougher-skinned berry. Pack the berries into freezer-safe containers (or bags), leaving headspace. Seal and freeze. Wash before using.

If want to freeze crushed or pureed blueberries, wash the berries first. Then, crush/puree your berries. Mix about 1 cup of sugar into each quart of berries. Stir until sugar is dissolved. Pack into containers, leaving headspace; seal and freeze.

If you're looking for a safe way to freeze just about anything, check out the National Center for Home Food Preservation.

When freezing any fruit, the quicker the better. The quicker you freeze the fruit the smaller the ice crystals are that form. The smaller the ice crystals, the less mushy the fruit will be when defrosted. The quickest method I have found is using Liquid Nitrogen. The results are always great. I remember seeing an example of doing it on FoodTV. I will see if I can located it for you.

I wash, puree and then pour the puree in ice cube trays... same for strawberries, etc. I use the ice cubes for a number of things, drop one in green tea, melt for pancakes, etc. A nutritious drink is mixed berry cubes melted, water and heaping tablespoon of chia seeds.

If you want whole blueberries, just freeze them in a bag and need to use, rinse under warm water and they are as good as the day they were picked. I have a number of blueberry bushes and freeze and use all winter.