Primary

A crock, bowl, bucket, pail, or other non-reactive, food-safe vessel in which the initial, or primary fermentation takes place. The primary should be capable of containing 1/4 to 1/2 more volume than the volume of the must it will contain to allow for a rising of the cap and a sufficient ullage above the cap to allow a good aerobic fermentation. Thus, a 1-1/2 gallon pail is about right for a 1-gallon batch of wort, although a larger vessel is okay. Typically, the primary has a large mouth to allow easy access. It should be covered during fermentation to prevent dust and airborne bacteria, molds and wild yeast from blowing into it, but should not be air-tight. Also known as the primary fermentation vessel.