Carbonating the Cider
If you want to carbonate your cider you can do it one of two ways. You can artificially carbonate, which requires further carbonation equipment and can give a slight taste to the cider. Alternatively, and preferably, you can naturally carbonate via further fermentation. Be warned that carbonating via fermentation comes with risk of exploding bottles. Also, you can’t sanitize the cider as this will kill off the yeast that is needed to carbonate the cider. For that reason, this is only recommended if the alcohol concentration in the cider is high enough to preserve it from bacteria.
In order to carbonate you will need to add a bit of sugar to the cider or a small amount to each individual bottle right before bottling. Once the bottles are filled with cider, you seal them up and wait. When the cider, with dormant yeast, comes in contact with the sugar, the yeast will be revived and will turn the sugar into alcohol and carbon dioxide. With the bottles sealed and the carbon dioxide unable to escape the gas will carbonate the cider. The risk is if the pressure in the bottle becomes too great, the bottle will rupture. For this reason, if you plan to carbonate your beverage make sure to use bottles that are built to hold the pressure. Look for a concave bottom on the bottle to tell if it is built for pressure (check a champagne bottle for an example). One alternative is to use plastic bottles instead of glass ones, but this isn’t recommended if you plan to age the cider.
It is possible to make a sweet or semi-sweet carbonated cider, but the techniques are delicate. One is to add a sweetener that yeast can’t ferment. Another is to pasteurize a sweet or semi-sweet cider, then inject carbonation into the cider. That technique requires additional carbonation equipment. Lastly, you can always bottle up the cider when it still has a bit of fermentation to go, wait a day or so, then pasteurize the cider. This last one is very much guess work and has four potential outcomes. One, the bottle explodes. Two, you end up with a still sweet or semi-sweet cider. Three, you nail it and get your carbonated sweet or semi-sweet cider. Four, you wait too long and end up with a sparkling dry cider.