Hops A-Z: O is for Oils

As an exercise in starting with little, losing most of what's left yet still making a huge impact, hop oil utilisation is an A+ example.

There's precious little to start with - the oil fraction makes up perhaps three to five percent of a cone's weight and sometimes substantially less. Then the brewing process reduces the oil content even further as much of the oil is vaporised in the boil and exits swiftly up the chimney.

Great background aroma for the brewhouse, not so promising though for the nascent beer. So, late additions (so less boil time) and/or dry hopping (mid or post-fermentation) are the solution to oil retention and takeup, delivering the specific aromas that certain hops are renowned for.

The majority of the oil's content (80-90%) is the hydrocarbon fraction; that is, consisting of hydrogen and carbon. It's made up mostly of terpenes (such as myrcene) and sesquiterpenes (alpha-humulene and beta-caryophyllene). Yes, there's a difference between the two. No, I'm not going to try and explain it. This is an irreverent guide to hops, not Biochemistry 101.

High levels of myrcene, as found in varieties such as Cascade and Amarillo, give pungent citrics. Not surprising, perhaps, given that citric fruit has myrcene in there as well. High levels of humulene, present in the 'noble' hops such as Hallertau, provide a characteristic spicy note. As the ratio of humulene to beta-caryophyllene increases, so does the spiciness (compare the fuller spice flavour of Hallertau Tradition with a 6:1 ratio with the slighter effect offered by Willamette at 2:1).

The oxygenated fraction (hydrogen, carbon and oxygen) is where perhaps most of the standout aromas reside. Geraniol has an obvious floral scent. Eugeneol offers spicy, clove-like notes. Beta-ionone carries a complex woody touch. The delightfully named linalool is reminiscent of mint, cinnamon and rosewood. And then there's limonene with - yep, you guessed it - the great smell of oranges.

I'll dwell on that last paragraph a little longer. Because beer writers, reviewers, brewers and fat-mouthed topers often have the piss ripped out of them for suggesting that beers taste of certain herbs, spices and fruits. That it's just florid hyperbole. It's not. Because it's not just a happy coincidence that certain flavours and aromas land in beer. They weren't put there by the beer fairy. Hops share basic biochemisty blocks,including those oxygenated terpenes, with other plants. So nobody should be surprised that a hop imparts a particular fruit or spice flavour. It's the same chemical. It *is* the same flavour.

Here endeth the lesson ;-)