Negative airlock

[Skoti]

I put a brew down on Friday and within a few hours it satarted bubbling away quite happily .
About lunchtime today (monday) I noticed it had equalised and when I had a look at midnight it had started sucking back .
As far as I know there's no leaks in the barrel and if there were I'd expect it to atleast equalise , but sucking back ?
Any ideas or should I just put it down to midnightitis

[db]

what temp was the brew at when it started bubbling backwards?
if there's little or no co2 being produced from fermentation, & the brew is warmer than the air temp it will suck air in to the fermentor

[Skoti]

Well I just had a look and brew temp is 21 deg the same as the other two brews I have going at the moment .
Tempreture in the garage is 18 deg .
Hmmmm strange .

[beerboy]

Do yourself a favour and throw away the air lock and the lid and use glad wrap.

[NTRabbit]

Mine only sucks air in when there is a big enough temperature drop in the wort after adding the lid, but before the yeast has a real chance to go hyperactive. Doesnt last long though, and it usually doesnt let any air buble in.

[Skoti]

Thanks for your replies .
I did a bit of research using the search function here and came to the conclusion that I ought not to trust the airlock .
At least this'll be the case with this particular barrel .

[Oliver]

Having a "negative airlock" is a pretty good indication there are no leaks.

As has been said, when the brew has stopped fermenting and if the temperature drops, the gas in the headspace of the fermenter cools and contracts. It then tries to suck air in through the airlock to equalise the pressure.

Oliver

[Skoti]

Thanks for that Oliver .
It's only the second brew I've made in that barrel (#4) and I had airlock issues with the first brew too and that turned out fine .
I'm not going to worry about it , just resort to actually using the hydrometer
when brewing in this particular barrel .