The flavour compounds in hops can be extracted by the process of the boil stage of brewing. This is the traditional way to impart the hop flavour into beer and has been used for centuries. It is however not very efficient.

By solvent extraction, the same chemical compounds can be extracted much more efficiently. Supercritical carbon dioxide (CO2 sublimes at room temperature & pressure so it doesn't occur as a liquid except if the temperature & pressure are ramped up) can extract the resins and oils from the hops and the solvent can be gassified leaving pure flavour compounds behind.

This is method used by the huge national & multinational breweries as it helps produce a more consistent product and is a much more efficient use of hops.

Whilst the flavour compounds are in solution they can be separated into the individual molecule types so that flavours reminiscent of orange, lemon, fresh cut grass, spiciness etc. can be isolated. Beers made with a blend of these individual compounds can be made that would never exist using the boil method of extraction. Some beers have the individual compounds responsible for causing skunking by being light-struck removed so that packaging can be in a clear glass bottle with less chance of off-flavours.

Smaller brewers may stick to the traditional method of boiling as a flavour extraction technique for simplicity or to keep the beers they brew closer to their marketing ethos of a more natural, unprocessed beer.