Bung

1. A sealing stopper, usually a cylindro-conical piece of wood, fitted into the mouth of a cask. A safety valve is sometimes used during secondary fermentation to maintain pressure at a maximum of 300 grams per square centimeter. 2. In homebrewing, the rubber or plastic seal into which the fermentation lock is fitted for secondary fermentation in carboys. 3. British slang for a publican.