While some people may use the terms interchangeably, hoppy and bitter don’t mean the same thing. Bitterness comes from hops, but the timing makes a big difference.
Bitter beers use hops early in the brewing process, while hoppy beers include the hops at the middle and end of the boil to balance out the bitterness with the hop aroma and flavor.
With that being said, you can have a beer that is hoppy but not bitter. Or, you can have a beer that is bitter but not hoppy. These two characteristics are a product of the brewing recipe and process: they go hand in hand.
Hops are not bitter until they are boiled. The amount of bitterness they give to beer depends on the amount used, the amount of time they’re boiled, and when they’re added to the boil.
The chemical composition of hops imparts bitterness in beer almost as soon as the hop hits the boiling wort. The longer the hops boil, the more bitter your beer will be.
To say that a beer is hoppy is saying that the hops are so present in the brewing process that you can taste them in the final product.
The opposite of a hoppy beer will be a malt-forward beer. All beers have at least a little bit of a malty flavor.
Typically, when a beer is bitter, it means that lots of hops were added early in the brew. Their essential oils boiled away during the process and their flavors and aromas went along with them, leaving a bitter taste.