Add the water and husks to a large pot and let boil for 5 minutes.
Remove the husks (your stock will go bitter if you leave any longer), giving a quick squeeze back into the mixture as you pull them out. Remove the liquid from heat quickly and measure. (Accounting for some loss in heat evaporation and absorption from the husks, it should be 44 fluid oz, give or take).
Place back on high heat until liquid is reduced by 50 percent, then add the sugar.
Add the citric and malic acid according to ratio based on citrus type.*.
Remove from heat, filter, bottle and refrigerate.
*Acid ratios by based on citrus varieties:
Lemon and lime: 3% citric, 2% malic
Orange and grapefruit: 2% citric, 1% malic
Mandarin, etc.: 1% citric, 2% malic.
Note: This recipe can easily be scaled up or down based on how much supply you’re working with or the volume you’re aiming to produce. Citrus stock can be kept fresh for three days or frozen for one month.