[Newb question] commercial.. Cereal/nut taste

It's very hard for me to explain this but I'll try... When I open a commercial beer bottle (or quality homebrew) and I put my nose next to the opening, there's always a good and pleasant aroma. Also, there's a pleasant "cereal" / nutty / sweet taste.

I love this taste and aroma but I don't know what within the beer makes this. Is it the malt, is it the grains, is it the hops, is it the yeast.. Any ideas?

If you think it smells like Grape Nuts,then it's the grain.GN is made from malted barley.

Try brewing all grain or even partial mash. Smell the raw grains. They'll drive you wild.

It is the Grains (Malted Barley).

I've brewed my first all-grain recipe (using BIAB method), and oh boy what a huge difference it makes vs extract!! I'm not turning back to extract brewing.. ever!