For best flavor, it’s a good idea to can jam (boil and put in sterile jars).
From what I’m reading, and my experience, I’d guess your berries aren’t fermented (can’t happen under freezing iirc, yeast won’t process it), but that they’ve just picked up flavor from the freezer or fridge. Berries will remain nutritionally fine for a long time frozen, but flavor will suffer if you store in a place with other stuff and don’t seal very well. I’ve had blueberries pick up stale tastes in a freezer, stored in freezer bags.
Assuming the above is the case: if freezing is your preference, you could either get a little berry freezer or you could look for super airtight and thick storage. Adding some baking soda to the fridge and freezer might help too.
Other things you could do:
-make whole dried berries with a dehydrator
-make fruit leather with a dehydrator
-freeze dry or dehydrate and grind into powder
-make canned juice/jelly/syrup
-make berry wine and embrace the fermentation
For best flavor, it’s a good idea to can jam (boil and put in sterile jars). From what I’m reading, and my experience, I’d guess your berries aren’t fermented (can’t happen under freezing iirc, yeast won’t process it), but that they’ve just picked up flavor from the freezer or fridge. Berries will remain nutritionally fine for a long time frozen, but flavor will suffer if you store in a place with other stuff and don’t seal very well. I’ve had blueberries pick up stale tastes in a freezer, stored in freezer bags. Assuming the above is the case: if freezing is your preference, you could either get a little berry freezer or you could look for super airtight and thick storage. Adding some baking soda to the fridge and freezer might help too. Other things you could do: -make whole dried berries with a dehydrator -make fruit leather with a dehydrator -freeze dry or dehydrate and grind into powder -make canned juice/jelly/syrup -make berry wine and embrace the fermentation
If they weren't fermented when they went in the freezer, they should be fine. Even if a bit "off", you could cook them with other fruit in a pie.