Espresso pots make a biting, concentrated coffee -- not true espresso, mind you -- but as close to the real thing as you can get without a machine. Also called moka pots, espresso pots work simply: Fill the lower chamber with water, set the coffee grounds in the filter above it and bring it to a boil. The steam passes through the grounds, condenses on the inside of the moka and drips into the upper holding chamber. Aluminum espresso pots work the same as stainless steel -- but they react with the acid in coffee and change its flavor.
Foods with a pH less than 7.0 are acidic. Coffee has a pH of 5.0 -- slightly less acidic than tomato juice -- and, like all acidic foods, reacts with aluminum. The most notable change that occurs in coffee when made in aluminum espresso pot involves taste: Aluminum imparts a metallic, tinny taste to coffee that increases the longer it stays in contact with the metallic area. Coffee doesn't leach enough aluminum from the pot to hurt you, it only affects the flavor. You can minimize the effects of the reaction by starting the coffee with hot water -- the faster it boils the better -- and rinsing the pot with hot water as soon as possible after use to prevent oil buildup. Never wash an aluminum moka pot in the dishwasher -- use mild dish soap and water.
Stainless-steel espresso pots produce a superior cup of coffee compared to aluminum pots. Non-reactive, easy to clean and dishwasher-safe, they need less maintenance and last longer, too. They also work with induction cooktops. Stainless-steel pots don't have the iconic octagonal base, but they have a rounded, sleek look that appeals to the eye.