I do not have a baby, but I have a sous-vide circulator (the light of my life), and I assume that other people who own sous-vide circulators might one day procreate. (Or maybe they already have!) For these offspring-having, sous-vide-savvy home cooks, I have great news: you can use your sous-vide setup to warm breast milk and baby formula to the perfect 98.6 degrees, without fear of overheating it.
The process is admittedly much slower than using the microwave or a pot of simmering water, but with that extra time comes the certainty that there is absolutely no chance of burning your baby’s tiny little mouth. Also, because the temperature of the bath will never go over what you set it to, you can set your bottle in the bath well before you’re ready for feeding, meaning you can get the milk or formula heating, and bathe, change, or gaze lovingly at the baby until it’s ready.
You can heat the milk or formula right in the bottle, without any jars or vacuum-sealed bags. I kept my test bottle from bobbing around by making a little sling out of plastic wrap and clothes pins. Just heat the bath to 98.6℉, place the sealed bottle in the bath, and let it hang our for 45 minutes. I tried this with both formula and cow milk—I’m afraid I don’t have access to the any breast milk—and both liquids reached their target temperature in under 45 minutes.