When we went to Canada where live minnows weren't allowed, I just super saturated water with salt and put the minnows in the brine over night. Too long and they look like minnow raisins, not long enough and you get mush. Then I put them onto cookie sheets and into the freezer. The frozen minnows were ziplocked and ready to fish. Once they thawed out you should use them that day. Refreezing didn't turn out too good for us, once they started to rehydrate a bit. I've done this with sucker minnows as well to use on tip ups. I was poor, so nothing went to waste when it came to fishing.