Starsan and sours

A very good point came up over the weekend while I was brewing a Flanders red. A bunch of friends from my home brew club stopped by and when I was sanitizing my Carboy with starsan they asked if I was going to allow the foam to remain. I said yes as the old saying goes don't fear the foam. Then one guy said what about the bacteria in the rosaelare blend will it be killed by the foam ? I honestly didn't know. I did know the yeast would be fine but the whole point of a sanitizer is to kill unwanted bacteria. So needless to say I played it safe and rinsed the Carboy of all foam just I case. What's the concensus will starsan kill Lacto pedio aceto etc ? Or will it not effect the souring capabilities of these bacteria.

It will kill them. However the foam is not of sufficient concentration at that point when your wort is added to the carboy to do anything about anything. Starsan is a pre-rinse sanitizer. Once the surface dries or you add your wort all bets are off. If your wort somehow became contaminated by wild yeast or bacteria when making something like a pale ale the foam wouldn't do anything for you. Same thing for your yeast culture if you add it to the carboy after the wort is there. Now if you're pitching the yeast and bacteria blend into the carboy with the foam and not after you fill it with wort then I can see the confusion. Eitherway it won't kill all the bacteria because the small amount of growth media that comes in your wyeast packet will still make the concentration of sanitizer remaining in the foam completely insignificant.

You could leave a gallon of starsan in the carboy, and after you added your wort it would still be diluted enough that it couldn't kill the bacteria.

+1.. no problem.

I kinda thought that may have been the case because I also know that once the wort is added the ph is so low it makes the starsan inert. Well I rinsed it to be safe ( probably contaminated it by rinsing lol ) but now I know for the future thanks !!!

Aschecte said:

I kinda thought that may have been the case because I also know that once the wort is added the ph is so low it makes the starsan inert. Well I rinsed it to be safe ( probably contaminated it by rinsing lol ) but now I know for the future thanks !!!

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It actually makes the pH too high for starsan to work. Starsan needs to be below a pH of 3 to be effective.