Why, when using a V60 filter coffee maker, do you have to let the coffee ‘bloom’ (by pouring on a bit of hot water just to cover the coffee, then waiting 30 secs). What happens if you don’t bother waiting?
You can check the answer of the people under the question at Quora “how long to let coffee bloom“
The 30 seconds period for the coffee to bloom is essential for the carbon dioxide trapped in the powder to escape. Wetting the grounds is necessary for a rounded flavour and extraction. In the pour over method you have complete control over the coffee flavour and quality, if you pour all the water in at once the subtle naunces of the flavour will be missing. For a very detailed explanation into what processes constitute an ideal pour over please see:- http://www.seriouseats.com/2014/06/make-better-pourover-coffee-how-pourover-works-temperature-timing.html
Blooming releases the CO2 in the coffee grounds. While it is not really necessary, for most doing it produces a better tasting brew to them. I suggest you try with and without blooming and see how you like it, you do not even have to be limited to 30 seconds, but that is a good benchmark. Like when I bloom, I usually let it it sit for like 45 seconds instead of 30.
The nice thing about the pour over method is that there is really no right or wrong way to use it, as allows for more flexibility and everyone would have different ways of brewing to suit their taste. It may take awhile before you get things dialed in and some practice to maintain consistency, but once you do, it will be a perfect cup every time.
I know that waiting 30 seconds is the preferred technique. To my taste, it produces a better cup of coffee. Good explanation of WHY in the Serious Eats article linked by Vivek.