If your 'barrel' has a sealed lid, you will need a way for the carbon dioxide to escape. This is mostly an issue with beer brewing. Large Brewers just run a tube from the top of their fermenter into a bucket of sanitized water. This is to prevent oxygen, wild yeast, and bacteria from affecting the beer flavored.
However, that is beer that you are going to drink directly. Many distilleries and most wineries have open top fermenters and take advantage of the local flora and fauna to add character to the ferment.
Bottom line, it's a choice, but if you have a sealed fermenter, the carbon dioxide needs a way out.