Cold Crashing + Blow-off tube = Soapy taste?

Hi all,
This is my fifth batch, but my first all-grain and (on a friend's suggestion) the first time I have cold-crashed a brew. So Friday when I took my final gravity reading and figured I was ready to rack to bottle, I chucked the whole works in the fridge.

I use a blow-off tube on my carboy and always have, but this morning when I pulled my carboy out of the fridge, I noticed that the line to the carboy from the blow-off tube was full of liquid from the blow-off bottle, which was holding water with sanitizer. Some of the liquid drained into the carboy as I pulled out the bung.

Friday when I tasted my brew after measuring the FG, it tasted pretty dang good. Today, after racking to bottles, the brew has an astringent, detergent-like taste. Since I was mostly done, I decided to go ahead and finish my bottling and let it sit for the next couple of weeks.

I guess I'm wondering if anyone has encountered this problem before, and how they might have dealt with it? And how I might avoid this happening in the future?

Thanks,

Suck-back. Nature abhors a vacuum. In your case, she filled it with sanitizer. I question cold crashing prior to bottling for this reason. Unless you take special measures, you will either suck back liquid or air (and potentially bacteria), and these should be avoided.

I cold crash in the bottle.

When you dramatically drop the temperature, you create negative pressure in the carboy that sucks air IN from the outside. In the future, remove any airlock or blow off apparatus when you first cold crash, and seal the top with sanitized foil. Once the temp has dropped and is stable after a day or so, you can bung it with a solid stopper because no (or very minimal) outward pressure is present.

Good luck with the beer. Hope it didn't get spoiled by whatever was in your blow off vessel.

When cold crashing, I switch my blow off tube to just bung with star San treated tin foil on the end. Never had an infection. As the liquid cools it'll form negative pressure and if fluid involved, will pull it in. Many will use alcohol (vodka, etc...) so if pulled in doesn't matter, but covering with foil works just as well and is easier. Now whether this was cause to your astringent taste is another question. Star San adds zero flavor. I spray my kegs down with it and don't bother draining the few ounces in there b/c it has absolutely no taste to it.
@Mcknuckle beat me to it during my typing apparently haha.

Yeah you likely siphoned some sanitizer into the beer. It happened to be once and I swore it would never happen again lol. Though supposedly, as long as too much didn't get into it you should be fine. I've had about 1/4 gallon of StarSan go into my beer (post-fermentation from a blowoff tube - it sucked my blow off bucket dry!) and the beer was fine!

Some things you can do in the future to eliminate the issue:

1) Ditch the blow off tube after 2 or 3 days in Primary! After that, switch to a normal airlock. By keeping the blow off tube on longer, you're letting more oxygen into the headspace due to diffusion. Small 3 piece airlocks obviously still let some oxygen in, but much less than the blow off tube. Once the risk of blow is over (i.e. the height of fermentation), there is no need to worry.

2) When cold crashing, change out your airlock for a solid stopper! Obviously cold crashing creates a vacuum (negative pressure) in the carboy. Even if you left the 3 piece airlock on, it would still stuck some StarSan (and a whole bunch of oxygen) through. If you cap the carboy completely, nothing will get in. You'll know this because when you pull the stopper after cold crashing, you'll get a whoosh of air rushing into it (but since you're racking anyway, contact time is minimal).

Or if you really want to solve the problem once and for all, buy a DryTap airlock from Better Bottle. I have one, and will never use a normal air lock again. I still use a blow off tube for the first couple of days, but then I put the DryTap on and never look back. You can cold crash with it and it will never allow air (or anything) into the beer. Check out this study for more info!

Another idea: https://www.homebrewtalk.com/f258/double-airlock-480990/