With the process below, why wouldn't the yeast eat all the sugar or explode the bottle whichever comes first? How does the yeast eat the sugar to make carbonation, yet keep the soda sweet?
Directions from Homebrew4less.com:
Sprinkle 1/8 teaspoon dry yeast (Red Star preferred) in 6-oz. of warm water. Let sit undisturbed for 15 minutes then stir gently to thoroughly dissolve. While waiting for the yeast to dissolve, shake extract bottle well, mix 2-1/4 cups of sugar and 1 tablespoon of soda extract in 1 gallon of lukewarm water. Mix until sugar is completely dissolved, then add yeast mixture stirring well. Pour 1/2 of this mixture in each 2 liter soda bottle and top off each one with plain water to within 1 1/2 to 2 inches of top. Attach a resealable cap and shake well. Store bottles at room temperature, preferably between 70 and 75 degree F for 4 to 6 days. You can tell by the firmness of the bottle how your carbonation is coming along. Move to cooler area if possible for another week of aging. When fully carbonated and aged the bottle should be just about as hard as a glass bottle. At this point chill thoroughly for 24 - 48 hours before opening and enjoying.