As the weather is cooling down, I've noticed the airlocks on my sours are reversing direction. There is still a water barrier, but the change in temperature is creating a vacuum that might be pulling in some of the airlock water until the airlock is reversed, and then possibly bringing in air.
The carboy is about a year old, so there is little or no CO2 production to correct the pressure.
I have several questions:
1. Is the vacuum primarily due to headspace volume change, or the liquid volume change due to temperature drop.
2. Should I top off the lambic with water? Will the topping off process introduce more oxygen and dilute the flavor making it worse off.
3. How bad is it for my airlock water to touch the beer? How much does it add to my beer cost to use cheap vodka for the airlock?
4. If I introduce fermentables or dextrins for Brett today, how long will the positive pressure last? Should I make it a policy to add (eg. 1/8 cup of sugar) every 3 weeks during the Sept-Nov months to keep positive CO2 pressure?
5. Sometimes I put a drop of iodophor to the airlock water. If this gets sucked into the fermenter will it kill the Brett in the beer, or affect the beer's taste?
6. I've been removing the airlock to remove the vacuum and allow the water to redistribute. Is the amount of air I'm introducing bad (or good)? My pellicle is long gone, and was very thin to start with.