Avent Microwave Steam Steriliser's contents will remain sterile for up to 24 hours if the lid is unopened. Just add water, load and place in the microwave for as little as 2 minutes. The small size means it convenient for travel, and that you always have a sterile bottle when you need one. It's also suitable for sterilising breast pumps - protecting your baby from particularly harmful milk bacteria until his immune system is strong enough. The unit uses the hospital method of steam sterilisation, which is quick, easy, and efficient, with no chemicals involved.