This item can emit carbon dioxide for honey, white wine and milk wine alcohol fermentation and can also prevent oxidation. It is easy to operate. You simply need to fill water into the exhaust valve, insert it to the cover of the brew barrel or rubber plug on the top of the fermentation container and then cover it with the lid. It can effectively prevent flies from flying into the wine/beer with a cover included. All of the fermentation process is automatic fermentation without manual control. And it can be repeatedly used for a long time. It is suitable for pure juice fermentation, such as white grapes fermentation, honey wine fermentation, red wine secondary fermentation and etc. Item Name: Brew Check Valve Material: Plastic Quantity: 1 Pc Features: Durable, Easy to Use, Portable, Brew Accessories Size: 17cm x 1cm/6.69" x 0.39" (Approx.) Notes: Due to the light and screen setting difference, the items color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement. Package Includes: 3 x 1 x Brew Check Valve