I use the spray bottle technique to save money on Star San. I also think it's easier than mixing up a full 5 gallon batch of sanitizer every time I brew.
I mix up one gallon at a time. Just add 6 CCs of Star San to one gallon of water.
Star San needs to remain under pH 3.5 AND be crystal clear. If your solution of Star San gets cloudy, it's (according to Five Star) no good. Hard water will make the solution go cloudy quickly. If this is happening to you, use distilled water. So, as long as it's clear and the pH is below 3.5 it's effective.
I suggest storing Star San solution in a one glass gallon jug. It takes a while but Star San will eat through standard plastic gallon jugs. I've had it happen and it's not cool.
Fill up a spray bottle and you're good to go. Just liberally coat surfaces in need of sanitizing. If you have a larger job, like a keg or a carboy, use what you need to sanitize (already clean items) and pour the Star San mixture back in the gallon jug.
I use a syringe to measure the 6 CCs needed.
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