Glass carboys are great for fermenting because they never scratch or break down over time. Plus, glass does not hold odor, which could impact taste. This carboy uses a #6.5 Stopper or a Small Universal Carboy Stopper. We recommend this larger-capacity 6-gallon carboy for use as a secondary fermenter, especially for winemaking or when brewing lagers or high-gravity beers. It can also be used as a primary fermenter for 3-gallon batches of wine.