Picking up a handful of Amarillo hops and taking a whiff should give you the unmistakable smell of fresh oranges, like peeling a clementine. But you may also, depending on when the hops were harvested, get a little lemon, lime, or spicy rye. Brewers like Amarillo for its versatility, adding it to pale ales, IPAs, and ESBs (Extra Special Bitters) to produce a complex citrus character.

Amarillo is one of 265 hop varieties explored by Julian Healey in a new book, “The Hops List’’ (available on Amazon), which he’s touting as the world’s first dictionary of hops. In the book, Healey runs down some of the world’s most popular hop varieties from A to Z, quoting professional and amateur brewers on descriptions of each hop and how they use them. Serious brewers can also find information on alpha acid composition, cone size, and ease of harvest, among other characteristics of the flowering crop.

“I really want it to be the most comprehensive reference guide on beer hops, the kind of thing every brewmaster has in his collection,’’ says Healey.

Beers are composed of four relatively simple ingredients: water, grain, yeast, and hops. But scrolling through a digital copy of the self-published book, it’s easy to see why the term “hoppy’’ is a woefully inadequate description. Healey’s hops are “earthy,’’ “citrusy,’’ or “spicy,’’ giving off notes of “blossom’’ and “blackcurrant.’’ Some of the hops, like Citra, are ubiquitous, while others, like Elsaesser, are grown on very limited acreage and unavailable to most beer producers.

Healey, who runs a web resource called hopslist.com, got the idea for the book after scrolling through “Wine Grapes,’’ a 1,200-page book on the 1,300-plus varieties of wine grapes. His goal is to update both the site and the book as new varieties come along. His next step is helping brewers fulfill orders of hard-to-come-by hops.

“Hop supply is a significant issue and often means brewers can’t bring their most successful beers to market when they want to,’’ says Healey. “Some of the ‘seasonal’ or ‘limited edition’ beers you see are only touted as such because the ingredients are inconsistent or unavailable all year round.’’

Hops, like the beers themselves, are subject to trends. Bitter used to be better, but many brewers are now eschewing that trend in favor of aroma. Mosaic, for example, is a variety prized for its clean notes of mango and stone fruit. As for what’s next in hops, Healey envisions brewers experimenting with darker styles like porters and stouts, mentioning a porter from a brewer in his hometown of Melbourne, Australia, as an example.

“The mango-citrus aroma somehow goes so well with the rich, dark, smoky malts,’’ says Healey. “It’s absolutely intriguing. I can’t wait to see more of this.’’

Gary Dzen can be reached at gary.dzen@globe.com. Follow him on Twitter @GaryDzen