Depending on the microwave the steriltwin can be sterilised in 4 6 minutes and can hold up to 4 bottles sterilising is crucial at this stage as a babies immune system is not yet high enough to fight off harmful bacteria in milk with the steriltwin sterilising will be quick and effortless it can remain sterilised if left unopened for upto 24 hours ensuring your baby is not in contact with harmful bacteria if you are out of the house and have no access to a microwave cold ste