OK, no rinsing next time! I'm noticing the ones that taste off are the ones that were the most ripe when frozen. I think next year, I'll pop those in my mouth & freeze the rest (dry!) Thank you both for your feedback. I appreciate it.

Never ever rinse them, unless you doubt the source. Same for raspberries, blueberries. I think that's where the ice crystals came from; berries should be frozen dry on the cookie sheet, then bagged. They should also be perfect, as freezing will not improve a sub-par product. Freezer grade plastic bags are far superior to containers, as you can press the air out. You can definitely rinse these bags and reuse them, too. I've frozen berries in this fashion for a long time, and they keep beautifully right up until the next harvest. (Your freezer should also be cold--set at zero.) I can't imagine where mold could come from, unless the berries had some moldy ones to begin with.

Yes to the ice crystals, but that doesn't worry me. I've always seen that with frozen fruit & it has never altered the flavor before (to my amateur tastebuds anyway). The volume remains the same also. But to answer your 3rd question, they do suddenly taste "off". It's not all of them -- maybe 10%, but since you can't tell before you take a bite, it's like playing blackberry roulette. They aren't moldy, thankfully. I had never heard that bags are better for freezing than containers, and that's a disappointment. I much prefer the stackability & reusability of the containers (and confess that I love my lock&locks). Hmmph! We got a chest freezer this year & I'm hitting a learning curve. (Another topic entirely was my mistake to NOT blanch the green beans.) Thanks for all your advice & the syrup is a wonderful back-up plan.

Describe what you mean by "went bad."

Are the fragile berries surrounded by ice crystals? Is their volume less than that of six months ago? Do they taste "off?" If that's the case, it's because you were given advice that, while very good, is incomplete: The airtight container should be a bag with as much air as possible sucked out through a straw, not Tupperware or RubberMaid containers; and the freezer should stand alone, not be attached to a refrigerator that has one or both doors opened and closed umpteen times a day, which leads to temperature swings instead of remaining a constant zero degrees F or less.

If they're not moldy, cook them with a little granulated sugar and some lemon or lime zest and have pancakes with blackberry sauce for breakfast tomorrow. And invite me, please.