If you taste a moderately bitter beer of, say, 40 IBUs against the same beer spiked with perhaps triple that, the first 10 seconds will feel exactly the same. It takes a while for the bitterness to grow on your tongue,. and it will build and build for nearly a minute. You almost have to watch the clock as you try this and force yourself to pay attention for far longer than you are probably accustomed.
I recently sat in a room full of people as we blindly tasted two otherwise identical beers of 40 and 130 IBUs without an upfront explanation and watched close to half the room fail to tell them apart. It’s harder than you think.

On Bitterness
Randy Mosher
In All About Beer
July 2014