The airlock is an essential part of your beer brewing gear, and it is also essential to use the right type of liquid to fill it with before you start the fermentation.
It’s not rocket science, but there are rather a few recommended liquids with a few advantages and disadvantages, so once you understand these few important facts you won’t have to worry about it ever again.
Simply put, what should you use to fill your airlock?
You can use StarSan/water mixture, vodka, or water but it is unsafe to use water due to possible bacteria infection of the wort. StarSan/water mixture and vodka are the safest options you have. My choice is StarSan over vodka or water, I’ve been using it since day one without trouble.
By the way, did you know it’s possible to ferment without an airlock?
Why even boiled water is not a good choice for airlocks
Water can contain bacteria and organisms that can spoil your beer if the liquid reaches your wort.
By boiling the water at 212°F (100°C) you kill all dangerous bacteria and make the water safe for use, however, when it cools down it no longer has the properties that will prevent the bacteria from growing once again in it.
Those tiny organisms are sneaky and if they get into the opening at the top of the airlock from the air, they may as well reach the wort below.
The odds of bacteria getting through the airlock and infecting the cool water in it are low, but never zero.
StarSan/water mix or vodka for airlocks?
The everlasting sanitizing properties of vodka and StarSan/water mixture will completely neutralize the odds of any bacteria growing within the airlock, so you won’t have to worry that some will end up in your wort.
StarSan will keep the liquid sanitized by default, and the high alcohol percentage in vodka will kill any grime instantly.
These are definitely the safest liquids to fill your airlock with and I personally have been using StarSan/water mixture since day one.
Moreover, If I had to choose between these two liquids, I would always choose StarSan over vodka. Vodka has a high ABV that will work great at the beginning, but it will evaporate quicker than StarSan will lose its defending properties.
If you need quick fermentation that lasts for 7 days or so, vodka could work, but StarSan will remain effective for weeks.
You’ll also always have some StarSan/water mix at the side when you brew, so it is easy to simply pour some in the airlock after you sanitize the fermenter.
Furthermore, even if you accidentally spill a cup of vodka into your wort it won’t break the beer.
Can StarSan be dangerous if it ends up in wort?
I knew you might think of this, and this is exactly what bothered me in the beginning. However, StarSan is not dangerous, and do not fear it.
Starsan is a sanitizer that protects your beer from unwanted bacteria and organisms that may hurt it, so it is a good guy and after all, it is not poisonous in small amounts.
Simply put, a small amount of StarSan in your fermenter won’t do anything and it won’t poison you nor do any single damage to the beer or human.
As a matter of fact, homebrewers including myself keep some Starsan/water mixture foam in the fermenter before we start to pour in the wort and it never resulted in bad practice.
Star San foam is extremely difficult to get rid of and letting it remain in the fermenter is easier, so why would you risk contaminating the wort by rinsing the fermenter if it is not necessary because Star San Foam is perfectly safe (A deeper explanation on the topic).
How full airlock needs to be?
You’ll see the marks which will indicate how much liquid is safe to pour in. However, you don’t need to make the airlock full, an inch or two of liquid is enough.
Always pay attention to the remaining liquid in the airlock. Do not ever let it evaporate completely! The Co2 needs to form on one side and work to get through the other side, if there are no passing bubbles, there’s not enough liquid in the airlock.
If you ever experience the airlock overflow caused by an aggressive fermentation, don’t worry it’s common for some beer styles and it’s not the end of the world.