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Is Starsan effective against yeast?

After resuming homebrewing again after a 2 year break, I started having pellicle appearing on my starters (after fermentation had completed), which has now spread to my plastic fermenting buckets so that the last 3 batches have been contaminated ("infected") - looking similar to this. The beer tastes fine, maybe slightly sour-sweaty. I plan to clean and sanitize all my equipment that's used post boil. I normally use Starsan to sanitize, but clearly the wild yeast are not affected. The made up starsan reads 2.8-3.0 on the pH meter.

Would iodophor or bleach be a better solution to get rid of this unwanted visitor?

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Just for fun I suggest you test it out. Mix up two batches of yeast and a batch of starsan, add it to one of the yeasts and see if you get any fermentation activity. I want to see photos! – Poshpaws Sep 12 '11 at 15:07

1 Answer

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Star-San kills yeast. Star-san doesn't discriminate across different microbes. Despite that yeast can survive a pH2 solution, the pH is not the killing action of StarSan, its the redox reaction on the cell membranes of microbes that does the killing. The low pH is just what indicates that StarSan is active, not how it kills.

Keep in mind too that StarSan is a sanitizer. It doesn't kill at 100%, neither does bleach or iodophore; otherwise they would be sterilizers. (Be sure you are diluting it appropriately, and not rinsing the sanitizer out with water either)

I'd be sure you aren't doing something later in your process that contaminates your cultures. Also, be sure you are cleaning your equipment before sanitizing. You can not effectively sanitize something if it hasn't been cleaned. Try something like PBW.

I'd also check your equipment. If you feel you are appropriately cleaning all your stuff out, then maybe you have a scratch or something that is harboring unwanted microbes. Recheck you process after sanitation, change your brewing location if possible. If all else fails, get new tubing and a bucket.

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Can you explain more you know it kills yeast? My understanding is that starsan is an acid based sanitizer, and yeast can survive at ph 2. I do clean then sanitize, as I mentioned in my question. – mdma♦ Sep 8 '11 at 11:42
I edited the answer to address mdma's comment. – brewchez Sep 8 '11 at 14:18
I'm with brewchez 100%, but I'd toss every hose and racking cane and buy new today. c – Dale Sep 8 '11 at 23:21
+1 Thanks! Great answer. The batches were made with old dried yeast, and old grain, so I wonder if the yeast lacked enough viable cells. I racked some yeast to mason jars and these have not developed any pellicle, so at least I know the racking cane is ok! – mdma♦ Sep 10 '11 at 1:32
I recently discovered my problem - after the long break I'd remebered incorrectly the quantities and didn't use the correct concentration. I often make half sized amounts, 2.5gal/10 liters, and with the metric conversion got the dosage wrong - turns out I was using only half the recommended dose, so understandable that some microbes were making it through to the beer. The surprising part was the relatively low pH2.6 even at half concentration, although proper concentration gives me pH2.2 that would make some sense with logarithmic pH scale. – mdma♦ Aug 1 '12 at 15:13

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