Regular pruning will prevent flowering. I end up forgetting to do that, and picking off new flowers on my basil, and it never turns bitter. I suspect if you let it produce a long flower stalk in full bloom, it might do that however. But that's a matter of not looking at it for weeks.

I don't bother trying, and I have not had it turn bitter.

The flowers are edible and taste like ... BASIL!

In my experience, basil cannot be stopped from flowering once the days begin to get shorter. At that time, the leaves are always bitter, no matter how much I prune the plants.

This is just my own experience, mind you. I've long decided to make the utmost of my young plants in the early part of the season but simply let them go to seed as they want as summer wanes. I love that gold finch go crazy over the seed heads!

I don't care for the taste of basil so don't grow it personally and so can't comment about any flowering leading to bitterness. That does happen with other edibles but I have not experienced that with most herbs....flowering does not alter the flavor substantially. And in fact, many herb flowers are just as tasty and flavorful as are the leaves. What removing or deadheading any flowers will do is encourage the plant to push out new foliage growth, which is what you want (as opposed to flower and seed production).

The best way to keep basil from going to seed is cutting it back, of course using the part that is cut off. I just cut back a group of plants that had just started going to seed that were maybe 18 to 20 inches tall, cut back to 6 inches. I've already done this multiple times this summer. The problem with letting them go to seed and not cutting them back is that the quality of the leaves starts to decline and lower leaves start to dry up and fall off. The plants just start to look sickly after the lush beauty before going to seed. So long as I keep them cut back, they keep coming back lush. I've frozen whole leaves, frozen chopped basil mixed with olive oil in cubes, and my wife likes having some dried. It keeps coming so long as I never let it go too far to seed.

Cut back with intentions to let it bush out. It's a constant cutting just above the last nodes. Can't stop flowering tho.

Good suggestions for keeping from flowering but the real issue is not bitterness but fibrous transition that occurs. If you're making pesto in a blender you will notice the difference immediately. Buds are OK, but once the plant buds open as flowers the entire tip becomes fibrous and tough and all that one can use for pesto is the leaves.

I would recommend not only picking flowers off, but trimming the foliage (and using it), too (then it can grow new foliage). I'm not that experienced with basil, yet, but I'm growing a bush kind this year, and it seems to do well with pruning (although I really would need to do a lot of pruning to stay ahead of the flowers). I can second that the flowers are edible.

I wonder if growing them in the shade vs. full sun affects the flavor.

There are side-effects to eating too much basil, I've discovered (I ate too much once), but you can eat a decent amount. It's great with tomatoes and olive oil on pizza.