Is the CO2 thing specific to letting roasted coffee sit X days before use and blooming? While I haven't really tried to see if blooming matters when it comes to taste (it's a good indicator of bean freshness), I can say there is a difference in days since roast impacting taste. Beans release gas after roast and if you have some too close to roast date the taste can be dramatically different from a day or two later. In fact I've seen recommendations of beans best used for espresso have rested for 5-7 days post roast.