I have the same problem with my milk getting a very horrible taste/smell, and unfortunately within 24 hours of pumping. I discovered this over the weekend when DH was practicing thawing out my frozen milk to give to DS while I'm away at work. The defrosted milk smelled like it was poured out of a rusty can, just absolutely awful. DS refused it of course. Trust me, I shed a few good tears about the 100 or so ounces of milk in the stash I have to pitch now . . . all in time for my going back to work which was today of course!
So, after I got home from my first day back at work this evening. Hubby and I did some testing in the kitchen about an effective way to bring the milk to the proper temperature so I can freeze the excess I pump. We also went out and bought a deep freezer this weekend because if I'm going through all this trouble to inactivate the lipase before freezing I want it around for a while :-)
Since DH is home part-time with DS we have a bottle warmer to make his life easier. What we found out using an instant read thermometer (about 6 bucks at the grocery store, target, etc.) is that our bottle warmer was actually the most effecient way to heat the milk to the right temperature. I use a PISA so I just take the Medela pump/store bottle, put it in the bottle warmer, add the water, hit the button and come back when it beeps in 5 mins. The brand whe have is Munchin, and I filled the measuring cup to the brim and that's the perfect amount. I held the instant read thermometer in several different bottles with varying amounts of milk and they all reached a temp of at least 180 degrees. With the cap on I'm sure the milk may even get a little warmer, I had the cap off to insert the instant read thermometer.
This makes me feel a lot better since I don't have to worry about putting the milk in a pan, etc. and worry about contamination, spilling and everything else. This will also shave off some time from having to scald the milk. I can just take what I pumped the day before which was unused (which is pretty much on it's last leg anyway) and any extra I pumped fresh that day and put it in the bottle warmer and it's done.
DS just started his part-time day care this week, I'm going to see if he'll take milk pumped from the day before. Hopefully so, but usually it has already gotten that 'signature' smell. At least we figured out the trick with the warmer. I'm sure my milk from Friday will have to be steamed to last until Monday when I'm at work.
Oh well, hope this helps someone else out there too. I've got some freezer samples going. I hope to post back in a week or so to let you know the results.