When I made mine, (out of plywood yet) it had alot of voids and did leak at first. I just kept coating it with polyurethane and letting it dry for several hours before testing it again. I just used water (saved the beer for last
)
I am one of those that believe that most if not all modern finishes are food safe once they are fully cured.
I guess you could use shellac the same way but, it might take more coats. Shellac is used on medcine pills and candy (think M&Ms) so we know that it is food safe.
Rog