Antifoams are compounds added to liquids that require foam control during agitation, and are typically silicone based or vegetable oil based. They are used in the brewhouse to prevent overboiling in the kettle and in fermenters to suppress foam formation during fermentation. Both allow for increased tank volume utilization. A secondary benefit is the increased utilization of iso-a-hops, which may allow for as much as a 15% reduction in hop usage. Antifoams also preserve foam-positive proteins, thereby enhancing the head retention qualities of the beer. When used in kettles they are bound to the trub and settle out in the whirlpool. When used in the fermenter they attach to the yeast and are removed when the yeast is removed. If yeast carryover into the final product is anticipated, vegetable oil antifoams should be employed. Addition rates vary depending upon application and beer type and must be optimized on site.