BeerBorg

I used one for the first time on my current ferment, a Belgian Dubbel fermented with WLP530. This yeast is notoriously active, and I have had overflow through airlocks in the past, even with moderate strength beers. So this time I left the volume a little low, and rigged a blow off tube into a bottle of One Step. Only one minor problem: nothing blew off! Now that active ferment is over, I'm wondering if I need to switch back to an airlock. To avoid suck-back, I raised the tube above the One Step. I have had foil over the mouth of the bottle from the start, as the basement is unsanitary. I think that to contaminate my brew, something would need to get around the foil, avoid falling into the sanitizer, and get all the way through 3.5' of tube into the wort. The special forces version of beer infections. Am I wrong here?

I've left blowoff tubes on the full time of fermentation but normally remove it and replace with the standard airlock just to be perfectly safe. While I doubt you will have a problem, why chance it?
Just my 2 cents.

Oxidation not infection would be the only thing I see to be worried about. But if you cold crash you "could" suck something up the tube if it's not covered. Cold crashing can create some impressive negative pressures.

Even natural cooling creates some suck back. In warm weather my ground water will only cool wort to the upper 80s. I use either cool night air or a ferm fridge to cool to pitching temps. The airlock always draws in some air and starsan. In this case the beer is only at 73, may cool to around 68. Whatever air gets drawn in would be so in any case, I think. The growler is covered, and still full of One Step.

I use to use a 3 piece air lock and think that is the best for primary and then switched to a s type if I did a secondary. This was when I had a 6.5 carboy or later with a 6.5 big mouth bubbler. Then I had a few problems with higher SG brews and a good dose of 0-4 or 0-5 so I started using a blow- off into a gallon milk jug with sanitizer well below the fermenter and worked. Now am using a Ss Brewtec 7 gal Brew bucket and they only want you to use a blow off tube on it so I do. Yes suck back can be a problem, but can also happen with air lock.

If I use a blow off tube to start with I always replace with an airlock after primary fermentation.

Like others have said, suck back can happen. The cold crash can definitley cause enough negative pressure to start it. And combine that with a sealed fermentation chamber like an old fridge. This is the setup I use. Two years ago, I left the blow off connected. During cold crash we had a strong cold front come through the area. The pressure outside of the fridge must have been different enough from the inside that it caused a serious suck back, once the water from the jug reached the bend in the tube, it started a siphon. It sucked a half gallon of water back into the the fermenter, and the jug was completely empty. It was amazing. Ever since then, I replace with an airlock just to make sure that doesn't happen again.

Interesting what can happen. I don't think mine can siphon, as the blow off bottle is on the floor below the fermenter, and the tube is above the liquid. But I will report any changes or results.
I still may install the airlock, but I would carry the fermenter out of the basement for safety.

Inkleg wrote:Oxidation not infection would be the only thing I see to be worried about. But if you cold crash you "could" suck something up the tube if it's not covered. Cold crashing can create some impressive negative pressures.

FWIW, I semi open ferment all the time and I never have oxidation problems, my beers age fine for 2 years without any issues. Never use an airlock at all anymore. Beers stay in fermenter from 2-4 weeks typically.

So I don't think that really is a concern. Maybe it is if you leave it in for months (secondary like things).

Also interesting. I just read a Brulosophy post about oxidation in NEIPA. I don't really worry about oxidation and I don't cold crash. I am careful about infection, as I ferment in an old musty basement.

John Sand wrote:Also interesting. I just read a Brulosophy post about oxidation in NEIPA. I don't really worry about oxidation and I don't cold crash. I am careful about infection, as I ferment in an old musty basement.

I don't cold crash either. Apparently he did, so that would have potentially sucked a lot of air into the fermenter, and cold wort can uptake a lot more gas then warm wort. (gas laws are fun).

So my bet is on that. Because I don't have that problem that I am aware of, and my own NEIPA attempts haven't turned out weirdly dark and caramel sweet.