Why is it important to seal air out when fermenting alcohol?!

Best Answer - Chosen by Voters

A sealed container will expand and possible erupt due to the build up of from the CO2 (gas) from the fermentation. So what you want is a blow-off tube or air-lock. These things can be made or purchased from your equipment supply shop. The reason we seal the container is to keep the beer/wine/cider free from undesirable microorganisms you know the wild yeast and bacteria and moulds that will spoil it. The is no risk of being sick from them just sick that you have wasted time, money, and effort in making something that tastes so bad it must be tossed out. We want the yeast that we used in a kit or free form recipe to do all the fermenting and nothing else. That is what the blow-off tube and air-lock does for us.

If alcohol kills bacteria then why is air not allowed in?
Well alcohol only kills certain bacteria and nor t all. If the like the Acetobacter aceti were to get to the liquid it can make acetic acid of the alcohol a ruin the cider. But other types can just make acids and spoil it before the alcohol is higher concentrations to kill them or prevent their growth. In addition the open container allow in oxygen that allow the bacteria to grow so the sealed container holding in the CO2 helps either kill or prevent growth of any that has gotten in.

Can it make you sick?
The chances are so remote I answer with an emphatic no.

You don't have to seal the air out. When stuff ferments, especially beer (cider is very similar) copious amounts of CO2 are produced by the yeasties. If you seal that in a barrel without a way for the CO2 to escape you will be washing beer or cider off of your ceiling. You need to give the gas a way to escape. You can use an airlock or a blowoff tube.

Having said that there are a lot of places that do open fermentation especially of beer and do not seal the fermentation vessel and the stuff ferments OK.

For things like most beers, ales, and ciders you need to ferment in a closed system with a airlock to let out the CO2. You want the yeast you pitch with to be the one growing and fermenting. Some Belgian beers (Lambic Ales) are fermented in open tanks so that wild yeast can get in and add different flavors to the brew. You don't want bacteria in any of it. It will give the brew an off taste that's pretty unpleasant. The brewing equipment must be sterilized before hand.

Air allows bacteria to breathe.Yes alcohol kills bacteria, but in the case of a cider or an ale , you dont have a great enough concentration to combat the bacteria. This is why is VERY important to sterilize all of your tubs, hoses, bottles when making beer/wine/spirits

Certain bacterias will foul your beer\wine\cider. This will happen before the alcohol content is high enough to kill bacteria and when it is high enough to kill bacteria it will probably kill your yeast as well.

If it received air while fermenting it would mold.