When your carbonated soda is on the assembly line, its container is first filled with a mixture of water, carbon dioxide gas and flavored syrup. The manufacturer then pumps additional carbon dioxide gas into the container's empty space. This prevents the gas in the mixture from escaping, putting the contents of the soda under pressure. When you open the a bottle of soda at home, you can hear the hiss of the carbon dioxide gas escaping; once the gas escapes, the dissolved carbon dioxide does as well, rushing to the surface and forming bubbles.

As you drain a bottle of soda, you leave more room for the dissolved carbon dioxide to escape; once all the gas escapes, it stops causing bubbles, and you're left with a flat soda. Small, hand-held carbon dioxide pumps exist that re-carbonate your soda at home or on the go. These handle-shaped pumps use CO2 cartridges and come with special bottle caps that feature rubber gaskets and tiny air valves. You simply equip your soda bottle with the cap, stick the pump's nozzle into the valve and shoot fresh CO2 into your flat soda, which re-pressurizes the bottle and makes new bubbles.

An alternative to re-carbonating pumps, at-home soda dispensers won't re-carbonate your pop, but they will keep it from going flat in the first place. These dispensers attach to the top of the soda bottle, serving as a base -- you set the bottle upside-down in your fridge so that it rests on the dispenser, which serves soda much like a beer or soda tap at a restaurant. Positioning the bottle upside-down makes it impossible for the CO2 ito escape, keeping the bottle pressurized and bubbly.

As soda dispensers illustrate, the key to keeping soda fizzy lies in keeping CO2 inside the bottle. Although flatness is ultimately inevitable over time, closing the bottle as soon as possible helps your soda retain its carbonation for as long as possible. Likewise, keeping the cap on tight and keeping your soda cool helps extend your pop's longevity.