IPAs like Bear Republic's Racer 5 and Coronado Brewing Company's Islander IPA have a distinct guava-like scent and flavor character. Is there a particular variety of hops that produces this, or is it a yeast or some more complex combination?
What you're tasting is the distinct flavor of west-coast hops. Most people liken it to a citrus, grapefruit, or sometimes orange peel aroma and flavor. You might be getting guava from the combination of tangy hops and a sweet, sugar-cookie base from the malt.
Racer 5 uses Centennial, Chinook, Cascade, and Columbus hops. I've heard that Islander IPA uses Centennial Hops, among others.
Amarillo and Cascade are generally regarded as having the most citrus-like flavors. To a lesser extent, Simcoe, Summit, and Chinook will have those qualities.
I think you'll find that brewing with any of the above, particularly Cascade or Columbus, and use heavy doses of late boil hops, along with some dry hopping, your beers will have the same nose and taste.
There is not a lot of information about the Islander IPA but Bear Republic uses Chinook, Cascade, Columbus and Centennial. My guess is that what you are associating with guava is the citrus/fruity character of Centennial and Cascade, although I'm sure there is a combination of all four. The aroma and flavor of centennial reminds me if mandarin oranges in beers like Bell's Two Hearted. The Chinook and Columbus will add some piney notes along with some citrus.
My buddy did a Pliny the Elder clone but he used 100% Simcoe. This thing came out like an orange bomb in the nose! It was actually really great. Simcoes can be hard to find if they're not in season though. I'm not even sure if Hopshack or other such places have them (and unfortunately can't check b/c my work's internet blocks them!)
MOSAIC, MOSAIC, MOSAIC! It can range in flavor, but in some beers I've tried it had a ton of guava flavor and aroma.
I recently brewed an almost 100% Mosaic American wheat (50/50 wheat and two-row), with a little Magnum for bittering plus several later flavoring and aroma additions of Mosaic (.5 oz @15min, 1oz @knockout, plus 1 oz Mosaic dry-hop 3 days). It had a ton of guava aroma and flavor. I used chico ale yeast to get a clean profile and let the hops shine through.
That said, a few years ago when this was asked, Mosaic probably wasn't being used and probably isn't in Racer 5. You can get tropical flavors from other hops, especially when layering several varieties (see below).
Old answer from a couple years ago, before I had tried mosaic:
The aroma you're getting is usually referred to as tropical or tropical fruits. It's related to the grapefruit which is common in citrusy American hops, but it's not the same. If you google around for it you might find some info, but most of these hops will just be listed as "citrusy".
Layering several different American hops - amarillo, centennial, cascade, columbus, etc - may give you this effect.
Brandon nailed it for Racer 5. There's also a new variety of hops on the scene that you might want to try: Citra hops. They're also tropical fruity and new enough that it will make people wonder which hops you brewed with.
Totally agree with Mosaic. I used them last year in a Mango Wheat and the combination was awesome, nice sweet aroma for the Mango flavor. Did well in a local competition.
I used Mosaic in a coconut IPA I just took off gas for the same reason and switched from Mosaic to Amarillo for a grapefruit IPA Shandy. Happy I did as I was blanking on the guava/melon sweetness of Mosaic when I originally built the recipe. The Amarillo is working well with it.
I would put money on Mosaic in this case as a key in the guava note.