Hi Zack
Please can you tell us why the distilled water last longer than tap? I thought our sulpher just escaped as a gass off the top. WHat is it about the pure distilled water that does different?
I think it's something with the lack of minerals in distilled water not buffering the pH, but I'll be honest that I'm not 100% sure. My understanding is that often times tap water is too hard, which can cause the StarSan to degrade or something over time and cause the pH to rise above levels where the solution can adequately sanitize. Distilled water works better because it doesn't have the minerals that makes water hard (calcium and carbonates), so the StarSan's pH and active ingredients stay effective.
That's my understanding, anyway. It's been born out in my experience. When I lived in Pittsburgh the city tap water was really hard. I'd use it to mix up a batch of StarSan, but in a few days it would be really cloudy and the pH would have risen. Over a year or so ago I saw someone in a post here on the forums say that their StarSan lasted months when they made it with distilled water. In my experience this is true. I mix up a 5gallon bucket only about once every 4 months, and only stop using it when it either runs out or the pH starts creeping up.
Using my "old" StarSan hasn't lead me to cross-contamination yet, and I'm even using it on Brett and wild yeast batches with equipment that I share with my Saccharomyces-only batches.
