How do you extend the life of formula milk? I understand that you can only keep it for a max of 1 month.

Geez! I haven't thought of that. Cause I don't usually stock powdered milk for baby. When I don't stock I mean don't buy more than what she needs for the month. Cause I've already calculated how much she would consume. I anyway transfer the powder from packs to a used tin can (more airtight than keeping from pack/sachet and scooping from there).