Airlock on secondary - flow reversed

[oisinboydell]

I have a stout I brewed from extract and steeped grains currently in the secondary fermenter. When I first racked it to the secondary the airlock bubbled away for the first few days which is fine, then slowed down which I also expected since the yeast must have used up most of the available sugars.
Funny thing is now the airlock has started going the other way, i.e. air is being sucked from outside into the fermenter (although very slowly). Does anyone know why this is? I've checked and the fermenter is not leaking, so the only thing I can think of is a change in temperature causing the air inside to contract. I hope it isn't a sign of an infection? Any ideas or suggestions?

Thanks.

[Frothy]

during both aerobic & anaerobic fermentation the yeast still produces CO2 during respiration its just that it produces less during anaerobic as it can less completely utilise sugar (thus produing alcohol.) Is it stormy in your area? changes in atmospheric pressure? Some American guy wrote that his beer did this before a hurricane.

Matt

[oisinboydell]

Is it stormy in your area? changes in atmospheric pressure?

This sounds like it. A few days ago we had a couple of big storms, and the weather is still unsettled at the moment so its probably an atmospheric pressure thing (I suppose the fermenter with airlock acts like a giant barometer!).

I looked at it again this morning and the liquid in the airlock seems to have levelled out again. I'm not concerned about the amount of air that got in, since there is already loads of co2 in there which is sitting on top of the beer.

Thanks for the replies.