How to select good coffee bag one way degassing valve?

Now more and more people like coffee. With the sales of coffee more and more, the coffee bag one way degassing valve also followed up more naturally, so the question is how to select a good one way degassing valve?

The features of coffee bag one way degassing valve:

1. Ensure the coffee beans dry and mellow flavor.

2. Discharge the carbon dioxide which is separate out from roasted beans or roasted powder outside automatic.

3. To prevent the coffee bean or coffee powder are polluted by oxidation metamorphism.

4. Prevent the bag burst when the accumulation of carbon dioxide.

5. Ensure can not let the air get into the bag.

If accord with the above characteristics will be a good coffee bag one way degassing valve.