It’s real easy, too. Just boil the sugar and some water with some lemon juice, let it cool, add the rest of the lemon juice, yeast nutrient, and yeast, let it ferment for a week or two, then keg.
Okay, you’ll need these:
8 lbs sugar (more or less depending on how sweet or hard you want it)
Safale S-04 yeast (almost anything, even bread yeast will do in a pinch)
So draw a gallon of water, dump 4 lbs of sugar and a cup of lemon juice into it, stir it to make sure it’s all wet, and put it on high heat. Stir it occasionally to make sure it’s not sticking and burning. Let it come to a boil, remove the heat, and dump it into a clean fermentation bucket. Put the top on and let it sit for fifteen minutes to steam-sanitize the container. Then add another 56 or so ounces of lemon juice (reserving 32 oz), four gallons of water, and a teaspoon each of yeast nutrient and energizer. Verify that the temperature is below 90 F, then add the packet of yeast – hydrate it if you like, or just sprinkle it on.
Put on the top and airlock and stick it in a warm place for two weeks. The yeast will usually work better at warmer temperatures because of the high acidity of the mix. Stirring it occasionally in the first several days to a week will help too.
After a couple of weeks, taste it and see if you like it. It will be pretty dry and tart. Add sugar to taste (one pound keeps it very tart, two pounds makes it reasonably sweet), and force-carbonate it.
You may want to add a crushed campden tablet to stop fermentation and keep the keg from exploding, but you’ll have to force carbonate. You could also add artificial sweetener to taste, then 3/4 c of sugar dissolved into some boiled water and mixed in, then bottle it.