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?

  • 1
    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
    Commented Sep 12, 2011 at 15:07

3 Answers 3


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.

  • 1
    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
    Commented Sep 8, 2011 at 11:42
  • I edited the answer to address mdma's comment.
    – brewchez
    Commented Sep 8, 2011 at 14:18
  • I'm with brewchez 100%, but I'd toss every hose and racking cane and buy new today. c
    – Dale
    Commented Sep 8, 2011 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
    Commented Sep 10, 2011 at 1:32
  • 2
    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
    Commented Aug 1, 2012 at 15:13

So, I had a 1600ml starter for my lager and it took off aggressively. I had to put a blow-off tube on my flask. I let the tube drop into about 3 inches of star-San. When the starter was all done, I had a good quarter inch of yeasties in the star-San. I have read all over these forums that that yeast would be useless. It was soaking in the star-San for 3 days. Not one to believe everything that I read on the web, I decided to see what it would do in a small starter. I cooked up half a liter of wort and threw the star-San yeasties in. 8 hours later, the starter is cooking off like a rocket. So, no matter what you read, don't dump your blow-off star-San yeasties - they might just surprise you. Oh, and this was a yeastie batch that I harvested from a lager fermented wit a wlp800 vial, mixed with a 25% glycine solution and had frozen for 3 months. Hardy bunch of bugs, eh?

  • Hmm, the manufacturer states it is a fungicide, and Wikipedia states yeast is a fungus. "* Broad Spectrum Bactericide and Fungicide" fivestarchemicals.com/wp-content/uploads/StarSanTech-HB2.pdf Did you throw the StarSan into your batch as well? How did you filter the yeast out of the bottom?
    – Chloe
    Commented Jun 27, 2019 at 1:27

Star San will not kill wild yeast. I rotate the use of StarSan and iodophor, since iodophor kills wild yeast. Here's the reply I got from a chemist when I asked about it...

Broad-spectrum Germicides.

The term “Broad Spectrum” when applied to a sanitizer means that it will attack a wide variety of different types of microorganisms, including gram-positive bacteria (Listeria and Staphylococcus), gram negative bacteria (E. coli and Salmonella), viruses, fungi (both yeasts and molds), as well as many parasites. Broad-spectrum germicides act on microbial membranes, cellular enzymes, DNA, and protein. Iodine-based sanitizers have been used as antimicrobial agents since the 1800s and have a broad spectrum of activity They are a powerful sanitizer in strong acidic aqueous solutions. They are generally used at 12.5 to 25 ppm available iodine, and can cause staining on some surfaces, especially plastics.

Acid-anionic sanitizers are surface-active sanitizers, but negatively charged. Formulations include inorganic and organic acids plus a surfactant. Carboxylic acids (fatty acids) are some times incorporated as well. They are unaffected by hard water or organic soils. The dual function of acid is that it can be used for rinsing and sanitizing in one step. These sanitizers must be used at low pH. Activity above pH 3.5–4.0 is minimal. Acidity, detergency, stability, and noncorrosiveness makes them highly effective. Acid-anionic sanitizers are broad spectrum against bacteria and viruses, but not very effective against yeasts and molds.

Iodophors are considered broad spectrum anti microbial vs. Star San being a being anti bacterial. The actual label for Star San lists what it is registered to kill: E Coli and Staph A – the minimum baseline for allowing a claim of being a sanitizer with the EPA. Iodophor has proven effectiveness against not only gram positive and negative bacteria, but yeast, mold, fungi and viruses and is also a sporicidal agent.


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