Vacuum brewer also known as siphon brewer, balance brewer, or glass brewer refers to tools used for brewing coffee. A vacuum brewer works on the principle of suction. This suction is caused by the expansion and contractions of gases - mainly one type of gas - water vapor. A vacuum brewer is made up of 4 parts - a bottom container, where the water initially sits; a top container, where the coffee grounds initially sit; a syphon tube connecting the two containers; and a filter, that allows liquid to pass through (and gases), but keeps most of the coffee grounds in the top container.