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

Yes, my friends all said that opened formula powder can only be kept for 30 days (upon opening). They generally keep to that guideline. At most, they push it by 3 to 4 days and so far, no adverse effects. However, none of them tried extending the "lifespan". Guess you could opt for a smaller can if you are not using much. If I'm not wrong, the nutritional value of the powder may change once opened. Hence, it is probably better to keep to the guideline (usually stated on the can itself).