I learned to homebrew back in graduate school. At first, I used bleach as a sanitizer because it was cheap and effective. Later, as I became aware of bleach’s potential to cause off flavors (and pit stainless steel), I switched to iodophor and later Star San. In my lab, however, as in biology labs worldwide, there was a sanitizer I used almost every day — 70% ethanol (sometimes written 70% EtOH). It didn’t occur to me until recently that this could be used in a brewery.
Ethanol, combined with a little water, is an effective sanitizer. Scientists have figured out that it is most effective at a concentration of 70% ethanol (v/v, with the remaining 30% being water) — although it is almost as effective throughout the entire range of 40–95%. The water helps the ethanol penetrate bacterial cells better. In biology laboratories, 70% ethanol is most often used to wipe down lab benches. (Glassware is generally sterilized by being autoclaved.) When sprayed on a clean surface, it kills bacteria in a manner of seconds.
Seventy percent ethanol is safe to use on typical homebrew surfaces. It will not stain or etch glass, or countertops. Some plastics can be warped or crazed by ethanol, but — for obvious reasons — those types aren’t used in homebrewing. Ethanol is (very) mildly corrosive to stainless steel, but at the concentration used and time required for sanitation — as well as temperature and pH — this is not an issue. (And 304 stainless steel is still the preferred material for most ethanol plants, so . . .)
Ethanol is not a contact hazard. In fact, many hand sanitizers are alcohol based. And, if you pour off any excess solution, you don’t need to rinse vessels that have been sanitized with ethanol. And, to top it off, ethanol is fairly cheap. You can easily make a 70% solution from Everclear (which, at 190 proof, is 95% ethanol) and water — just mix 7.37 volumes of Everclear to 2.63 volumes of water. You could also slightly dilute a 151 proof (75.5% alcohol) distilled spirit (such as rum) slightly, although this would likely have a flavor.
At this point, one thing you might ask is, if 70% ethanol is so great, why don’t breweries it? Two words: “ka” and “boom.” Some breweries use isopropanol to spray fittings, but ethanol isn’t used a sanitizer because ethanol is flammable and ethanol fumes are volatile and explosive. In addition, although ethanol is fairly cheap, other sanitizers are cheaper. And when you need lots of a sanitizer, the costs add up.