Q: What does the airlock do?
A: The airlock (once filled with liquid) will create an anaerobic environment for your fermentation. This means that all of the carbon dioxide created from the fermentation will be released through the airlock, but the liquid will keep any oxygen from outside of the jar from coming in. Oxygen can cause mold to grow so having this setup greatly decreases your chance of growing mold!
Q: What is the difference between using vodka or water within the airlock?
A: Water is perfectly fine for most of the year as it really just keeps any oxygen from coming in to your jar. Vodka is great when you have fruit flies around. Some fruit flies can actually go through the top of the airlock, but once they land on the vodka, they vodka kills the fly and will keep everything sterilized.
Q: What to do if water level in airlock goes over "fill-line?"
A: You can take the airlock out of the rubber stopper and recap. Take the airlock top off and you can pour some water out. If it is overfilled, there might be some water that gets sucked into your ferment, which is totally fine! The water that gets sucked in will not do anything to the flavor of your ferment.
Q: What is the effect on fermentation if the jar lid is opened to push fermenting matter down in the jar?
A: It really depends on how often and how long the lid is off. Typically when you push the matter down once a day, it won't cause an issue. The main thing the kit provides is an environment without oxygen to reduce the chance of mold. As long as the matters are underneath the brine, mold is even less likely. Once you recap your jar, carbon dioxide will still be pushing out oxygen through the airlock so it'll create an oxygen-free environment soon after.
Q: Some fermenters recommend using weights to hold down fermenting matter. Is this needed for successful fermentations?