Hop pellets are highly processed hops consisting of finely powdered hop cones compressed into small tablet forms. Even though they look commercialized you can use them in home and commercial brewing applications. One thing hop pellets have going for them is by weight they are 20%-30% stronger than the same type of hop in loose form. These concentrated little pellets are first processed to remove the non-resinous materials in the hops, thus reducing the weight and volume of the hops. Most hop pellets are made form a blend of hops to maintain consistent alpha acid levels.
Hop plugs are whole flowers that have been dried and compressed into a plug. Many people say that the hop plugs produce a better aroma and flavor than the hop pellets. Though that is a point of personal preference more than anything. Because hop plugs have a small surface area their exposure to the wort is minimized and is less efficient for bittering. So you’ll need to use more plugs to equal the amount of bitterness imparted by hop pellets.
Whole leaf hops are exactly what they sound like, whole hop flowers dried and uncompressed. This is the original way beer has been brewed for centuries, but that doesn’t mean it’s the best way anymore. They are no more “fresh” than pellet or plug hops, they require much more space to store, and they don’t settle out in the kettle and fermenter as nicely as pellet hops do. Due to their loose leaf structure, they are more susceptible to oxidation and degradation than plugs and pellets. Finally, whole leaf hops run into the same problem as hop plugs, they don’t impart as much bitterness to your brew.
A lot of people have varying feelings when it comes to using hop extracts to fortify your home brew and impart that missing bitterness. My personal opinion is that it’s no different than using chili spices when cooking a dish instead of dicing up fresh chili peppers. Sometimes fresh peppers are called for because you want that added texture and moisture, but other times you’re happy with your meal’s consistency and just want to heat it up a notch. Same goes with hop extracts. It comes down to the brewer and his or her use of those extracts. If you’ve ever had a pint of Pliny the Younger, then you’ve had a fine brew that uses hop extracts in conjunction with pellets. Honestly, if a bitter beer is what you’re brewing then using hop extracts can be very beneficial because you would end up soaking up too much of your wort using tons of hops. Note: Use extracts sparingly at first until you have a real handle on the strength of flavor a small amount can impart on your homebrew.