formula freshness

[dkmom]

Currently I am giving my DD one bottle of formula a day. We would like to buy the larger size cans from Costco to save money, however there is no way we can finish the can in 1 month. Wanted to know why the formula expires 1 month after opening. We live in a dry climate so there is no issue of 'caking'. We were thinking of vacuum sealing half of the formula.

Wanted to know what the other moms who supplement breastfeeding do.

Thanks!
-Darshana