You can also obtain what are called carbonation drops. These are candy-like pieces of sugar made with a very specific amount of fermentable sugar - just enough to produce a known amount of carbon dioxide when the yeast ferments that sugar. Note, when you add these "drops" in an appropriate bottle - and by appropriate, I mean a bottle whose walls have been designed to withstand the pressure the gas will exert on the glass and with the kind of closure that will not fly off given the pressure inside the bottle - we are ignoring the few points of additional alcohol and are focused only on the CO2 the yeast produce. Realize, that all fermentation results in the production of ethanol (alcohol) AND CO2. Indeed, half the WEIGHT of the sugar you start with will become CO2, and for still wines, all that gas is encouraged to escape. For sparkling wines, we still encourage all the CO2 associated with the primary fermentation to escape and we want to trap inside the bottle only the CO2 produced as we "prime" the bottles with "drops", or known and very specific amounts of sugar to produce around 45 psi of pressure. Champagne is around 80 PSI. Your car tire is - what 35 -36 PSI
