Hi Ladies- My LO is 7 months old, and I've been pumping 3x per day at work for the past 3 months. I put my expressed milk in the Lansinoh milk storage bags, and place them in a cooler with two ice packs. I heard that you aren't supposed to combine refrigerated milk with freshly expressed milk, so I combine the expressed milk after they've been cooled to the same temp for a few hours. As soon as I get home I put the milk in the freezer. I'm finding that a lot of the milk I thaw out is sour. So... I don't know what to do differently. Any advice? I feel like I'm having to toss a lot of milk these days... and since I already have to supplement, this really sucks!