Step 1
Combine alcohol and lemon zest in a 1-gallon jug with a tight-fitting lid. Place in a cool dark place to rest for 1 month. Swirl contents of the jug every few days.
Step 2
Combine water and sugar in a saucepan over medium heat; stir until sugar is fully dissolved. Set simple syrup aside to cool completely 15 to 30 minutes.
Step 3
While simple syrup is cooling place a sieve over a large bowl and line with coffee filters. Strain alcohol mixture through coffee filters to remove all sediment. Replace the filters as needed until all the mixture has been filtered. Filter one more time to ensure all sediment has been removed. Discard coffee filters and zest.
Step 4
Add enough simple syrup to the alcohol mixture to reach the desired alcohol-by-volume percentage; refer to an alcohol content calculator.
Step 5
Divide limoncello among 6 wine bottles. Seal with corks. Allow to rest in a cool dark place for 1 month swirling every few days. Strain one more time to remove any leftover sediment if desired.
Step 6
Place 1 bottle of limoncello in the freezer and serve icy-cold. Store remaining bottles at room temperature.