As per Kyle above, YEs coffees fresher to roasting are expelling more gas than older ones that have degassed more. indeed a definition of staleness may include no more CO2 is released.
hitting beans with water shows that this gas is happening. But why bloom? that is supposed to get the gas out so water can come in.
Does it? if so for how much of what's ground? just cuz you get a mushroom effect does that mean all the grounds in there got wet??
there's a pretty good debate about "blooming" the coffee - and focussing on creating a bloom rather than focussing on really "wetting" the grounds
To this end, coffee afficianados like perger and rao among others are skipping the bloom and just stirring.
as a scientist gotta say i go with the chemistry of that: if the goal is even absorption of water by even release - agitating those grinds is going to to the business better than a bloom that offers little insight into the evenness of the wetting. Stirring ensures far less likelihood of channeling as water passes through too - would recommend reading/viewing rao on this point if interested.
so why not try it? forget bloom and just stir. see what that does to taste?
I've also found that coffees that are supposedly past their prime can be surprisingly flavourful given a good stir for ten secs and soak for another half minute and then the rest of the pour.
In other words another answer to the question "what is coffee bloom" - it may just be "a ritualised futzing with CO2 gas in coffee that has little proven benefit for flavour extraction compared to stirring but provides more "show" for charging 4.50 at a coffee bar"?
ps - a nice way to see if you've got the gas out of the fast 10sec stir of the slurry is that there are NO more bubbles coming out after that ten secs and as the coffee then sits for 30-45 secs total.