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Yeast overcoming Fermcap-S?

I brewed an APA (OG around 1.050, if I recall correctly) on Saturday and used Fermcap-S in the fermenter. This morning, I checked on it and it was blowing off. I’m writing this to see what, if anything, I did wrong, or is it common to have a blow-off even with Fermcap-S being used. Here are some extra details…

It was a 5 gallon batch in a 6.5 gallon carboy. I used 10 drops of Fermcap-S added directly to the carboy after running the wort off from the kettle, but before hitting it with oxygen. I used an oxygen cylinder with a aeration stone for about a minute. The yeast was a single Wyeast 1056 smack-pack, which I made a starter for about 24 hours before pitching into the beer. I used a stir plate. The beer itself doesn’t have anything exotic in it. 10.25# US 2-row, 10oz crystal 60, 3 additions of Zythos hops totaling 2oz, and a whirlfloc tablet. I didn’t use Fermcap-S in the boil.

Was a minute of oxygen plus a stirred starter too much? Did my yeast overpower the Fermcap-S? Could the Fermcap-S have dropped out early? Could my Fermcap-S be too old? I bought it last January and it’s been sitting somewhat forgotten in my fridge since. This was actually the first time I tried to use it.

On a somewhat related note, is adding the Fermcap-S directly to the fermenter risky in terms of sanitation?

What do you think? Thanks!

What was your temp.? I’ve used it 7-8 times, and the only blowoff was with Wy3068. Your headspace isn’t a problem, I put 5.5 gals in a 6 gal carboy.

I don’t use it in the fermenter, but seems like you might get better performance if the fermcap is floating on top of the wort rather than mixing it in - aerate and pitch your yeast, wait for the foam to subside, then apply the fermcap.

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