Other than banging the bag with a hammer then whirring the smaller chunks through a food processor, I don't know how to fix your brick, but there are some things to try to prevent it. It's moisture that makes the powder turn into a brick. For starters put your fresh buttermilk powder in a heavy ziplock bag--if you can manage it, the pressure zippers are better than the slider zippers. Then put the bag in an airtight container. Not a regular canister with a silicone or plastic ring, but completely airtight. OXO Pop or similar would work, or a bail topped jar with a new rubber flange. Put a Sugar Bear or a very dry piece of a broken clay flower pot (you can lightly toast either in the oven first) in next to the bag. It's less convenient having to open two things and dig in the bag instead of scooping from a canister, but that should keep most of the humidity out.

I should have realized that the wax coated cardboard container it came in wasn't going to hold up over time. I have the reverse problem with raisins! I haven't had good luck with those vacuum seal canisters keeping their seals, but might be worth the investment. Even a regular seal one would be better than just leaving it in the cardboard container like I have been. I have several of the ball topped jars with rubber flanges and they seal quite well. I guess I'll have to get another clay gizmo. I got one for my brown sugar and so far it is going good. But that one actually gives off moisture. I haven't tried it in reverse.

Well, start with a Ball jar. That might be sufficient without having to acquire anything.

I like Grainlady's suggestion of reusing a silica gel packet, too. That probably works even better than clay.

I haven't had very good luck with the Foodsaver canisters, either. They not only don't seal very well, but the way the release button is situated, it is way too easy to bump it and release the seal when it in sitting on a shelf, and not even realize you touched it. But I learned here on the CF, that Ball jars can be used and keep their seal very well! And you don't need to purchase the gizmo they make to seal the jars, either. Use a tack to punch a very small hole in the metal lid, loosely cover it with a tiny piece of electrical tape, and seal with either a hand held vacuum sealer, or with the accessory attachment hose. Works like a charm! I do put the lids in hot water for a minute or two before sealing, but I honestly don't know if this is a necessary step or not, it just seemed to make sense to do it. I used to wish they would redesign those canisters to work better, but since I learned about using jars, I have no desire to have better canisters. The jars are much cheaper, too! (Always a plus with me!)

Rusty

Make a little muslin bag of minute rice and keep that in the canister with your buttermilk powder. Regular rice helps some but minute rice, made to take on water instantly works better.

Thanks Linda, I have some minute rice. Seems like the silica gell packets would have a set amount they could absorb, but I'm not sure. I have two packets in there now but I was thinking that I should replace them now and again.