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I use a Raspberry Pi with water-proof temperature probes to monitor the temperature of my fermenting wort, and I feed the probe through the airlock to make direct contact with the wort.

Two out of my last three batches have resulted in an overflowing airlock. For one of them I had to remove the airlock (and temperature probe) and replace it with a blow-off tube. This is undesirable for me as I then have to attach the probe to the side of the carboy with insulation material.

The other batch that I have right now is flooding the airlock but is not so bad that I have to replace the airlock with a blow-off tube. I am simply taking a paper towel and attempting to absorb some of the wort in the airlock, and then refill it with vodka up to the top.

My worry is that the wort in the airlock will become contaminated as it is a mixture of 40% vodka and wort, and that the wort next-in-line to enter the airlock will become contaminated and then the whole batch will become contaminated.

I could obviously just take the airlock out, wash it, and put it back in. However I had my first contaminated batch and have become adverse to taking the airlock out for short periods.

Can the wort inside an overflowing airlock contaminate the batch?

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After having 2 airlocks fill and start clogging which resulted in me having to use a larger diameter blow-off tube. I just altogether stopped using air locks and retrofitted the fermenters over to Blow-Off tubes. I never have to deal with it again. You could snake your temp probe easily through the 1/2 dia blow-off tube. –  apesa Jun 18 at 2:24

2 Answers 2

I would deem this to be a very minor risk indeed. As long as you have a bit of alcohol (or anything that bacteria dislikes) in there, 15% would do, you will not have growth. The shape of the airlock would itself be sufficient to avoid contamination, a similar setup was used by Louis Pasteur when he disproved spontaneous generation of life back in the days, and his broth was uncontaminated for years.

Although it is comforting to have a disinfectant in the airlock the main reason for having liquid there at all is to decrease the amount of oxygen getting in to the beer.

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The answer: In theory No. See Korsbo's answer. Contamination from when you remove or re-insert the airlock is a bigger possibility. When you have cleaned your airlock, sanitize it (and the place when you will be inserting it). That will give you extra cover.

Why not stop using the airlock completely and just use an blow-off? Maybe drill a small hole in the block-off, just past the top of the turn, and insert your probe from there. This will allow the wort to happily escape, due to the hole being at the top, and past the bend, the wort should not escape there, and the wort that does contact the probe will then be on their out in any way.

You can maybe even consider sealing the hole (with probe inserted) with some silicon.

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Another thing: What does your airlock look like? The s-bend (left) or does it have the cap that fits over the pipe (right)? clker.com/cliparts/f/9/0/e/…. If you have the one on the right, then you can remove the lid and cap and put a blow-off directly onto the pipe. I think this airlock will also be easier to insert/remove a probe from. –  Atron Seige May 26 at 11:04
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Beware of using small diameter blowoff tubes that would fit onto the airlock. They can clog and result in a much bigger mess than you will want to clean up. –  jalynn2 May 27 at 14:17

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