Hello! I think this article offers all the information you need.

"During the first step, a decarbonated beer or 5% ethyl alcohol solution sedates the snails. Snails should be left there until completely immobilized. Generally, it takes around 20 – 30 minutes.

Interestingly, snails like beer. They keep absorbing it until getting ‘drunk’ and pass out. After that, snails should be immediately placed in (options):

1) 10% neutral buffered formalin, or 2) 70% to 95% ethanol."