Originally Posted by Kephren
Actually, 16lbs will cool it down way too much. One 7lb bag and 1 pint of water = 1 gallon. That will bring it down below 80 degrees and ready to pitch right away. Grocery store ice *should* be sterile. You might want to run sanitizer or bleach around the outside of the bag just to be sure, but it will work fine.
Ice bought in the stores - the bags you are talking about - is NOT sterile. Many ice manufacturers do heat up the water, but not to the point where it becomes sanitary and certainly not for reasons of sanitation. They heat it up because, believe it or not, it will flash freeze quicker if it starts out hot, and that helps it become so clear.
Besides, the bags tear while in the freezer. Haven't you noticed that? Factor in to that all the people who stick their grubby hands into the freezer to grab the bags...well, it makes me a little queasy to think about it.
Just know that store-bought ice is no more sanitized than the ice in your freezer's ice trays or what comes out of your ice maker!