thanks all. What I usually like to do is make 5 gallons and fill up the keg and push the sanitizer solution out during fermentation (free CO2) then I have a completely empty sanitizer keg when keg time comes around. So saving the sanitizer solution is always my goal but you’re all right. A year old is probably too old lol.
Cheers
After I clean and sanitize kegs (with a proper, active solution of Starsan) I
do use that old saved starsan solution, to purge the kegs like you do.
But with a note:
After about a month (or 2) that old Starsan solution becomes crystal clear (probably just like yours), with a layer of white sludge on the bottom.
Decant it, slowly and carefully, into a 6.5 gallon brew bucket or so, through a strainer (double paper towel in a large colander). Don't get greedy, leave the white sludge that has settled on the bottom of the original bucket behind:
As soon as you see that cloudy liquid from the bottom starting to appear in the stream, tilt the bucket back and stop pouring.
So, that cleared old solution of the Starsan may not be as good of a sanitizer anymore, but is great for 100% liquid purging of
clean and already sanitized kegs. The purging solution can be recovered and reused almost indefinitely.
I keep a full 6.5 gallon bucket of it around, just for that purpose. Its pH is 2.5-2.8, and you can always add some phosphoric acid to correct it. Nothing can grow in it AFAIK.
I keep it covered with a loose lid on top, but you got keep an eye on the underneath of lid and the headspace in the storage bucket, as it is damp and dark in there, and can grow some mold. So mop/clean that every few weeks with some "real" Starsan to prevent that from happening.