Warning: this article is ‘bout to get nerdy. Have you ever seen the “bloom” when you brew coffee? It is a very good indicator as to whether your coffee is fresh or not. When coffee is freshly roasted it is constantly giving off the gas CO2, carbon dioxide. This is due to the breaking down of the cell structure in the bean during the roasting process. Because of this degassing of CO2, many coffee companies have to include a small plastic one-way valve in the bag that their