Secondary Fermentation Dry Ice CO2 Purge

Oxygen contact is bad news for homebrews.  Once you pitch your yeast into the fermentor, you want to keep contact with oxygen at a bare minimum.  You need a little bit of oxygen to help the yeast reproduce and be happy at the beginning of the process (which is usually incorporated by aeration), but producing alcohol is an anaerobic process for the yeast.  That means oxygen can stall or stop the fermentation process (not to mention, if you have contamination in your fermentor from poor sanitation practices, oxygen will help the nasty stuff grow).

For the primary fermentor, your yeast are actively creating CO2 and displacing the existing oxygen in the container, so you don't have to worry about purging it.  However, in a secondary fermentor, a CO2 purge would minimize the risk of oxidization of your beer and contamination.

We learned a cool trick from our local homebrew store using a funnel and dry ice, and thought we'd share it here!

Quick reminders:

• Remember to use good gloves and/or tongs when handling dry ice! 
• You only need a small block--maybe the size of a full wallet or a deck of cards.
• Check your dry ice for dirt, and use a sink brush or sponge to quickly clean it.

Check your funnel for a small notch in the stem--this method will only work if there is a way for your purged gas to exit.

Place the sanitized funnel into your carboy, and carefully place a small amount of dry ice in the funnel.  

 

Since CO2 is heavier than air, the CO2 will sublimate off the dry ice, travel down the funnel, and displace the air out of the carboy through the stem notch.  Let the sublimating CO2 purge until you see the condensed air (what looks like fog) come out of the stem notch.  

Be careful when removing the funnel: water frost will form on the outside of the funnel, and you don't want to accidentally shake or knock this into your fermentor!