Why one hop smells of mango and another of pine

The oil inside the cone

Inside each hop cone are tiny yellow glands called lupulin. They hold two things brewers care about: alpha acids, which become bitterness when boiled. Then there are essential oils, which carry aroma. Hop oil makes up only a small fraction of a hop's weight, but it is responsible for almost everything you smell.

That oil is a mix of hundreds of compounds. Each variety has a different balance of them, shaped by its genetics, where it was grown and when it was picked. Our guide to hop varieties for beginners covers the common names. Here we look at what makes them smell the way they do.

The main aroma compounds

A few groups do most of the work.

• Myrcene. Often the largest single oil. Fresh, green, resinous and a little piney. Strong in many American hops.
• Humulene and caryophyllene. Woody, herbal and spicy notes. Higher in traditional European varieties.
• Linalool and geraniol. Floral and citrus, with rose and orange blossom notes. Present in small amounts but powerful.
• Thiols. Sulphur compounds that smell of passion fruit, guava, grapefruit and blackcurrant. Detectable at astonishingly low levels.

No single compound smells of mango. The tropical fruit note in hops like Citra and Mosaic comes from a blend: thiols, citrusy terpenes and esters working together. Your nose reads the combination as mango or lychee.

Pine, citrus and the old world

Pine and resin come mostly from myrcene and related terpenes such as pinene. Hops like Chinook and Simcoe are known for this. Grapefruit and orange come from a mix of terpenes and thiols. Cascade, one of the first American aroma hops, is famous for grapefruit and flowers.

The noble hops of central Europe, such as Saaz, smell herbal, spicy and gently floral. They are lower in myrcene and higher in humulene, which is why a Czech pilsner smells nothing like a hazy IPA. Hops from New Zealand bring their own twist. Nelson Sauvin is often described as white wine and gooseberry.

When the hops go in

Hop oils are volatile. Boil them for an hour and most of the aroma escapes up the chimney. Brewers control aroma by choosing when to add hops.

• Early in the boil: mostly bitterness, little aroma.
• Late in the boil: some aroma survives.
• Whirlpool: hops added after the boil while the wort cools. Many brewers hold the wort around 75 to 85 °C for 20 to 30 minutes, which extracts plenty of oil without driving it off.
• Dry hopping: hops added during or after fermentation. This gives the most intense fresh aroma.

Yeast also changes hop aroma. During fermentation some strains convert geraniol into citronellol, shifting rose notes towards citrus. Others release thiols that were locked up in the hop. This is called biotransformation. It is part of why a New England IPA smells so juicy.

Why that aroma fades

The compounds that smell best are often the most fragile. They oxidise and break down, especially in warm storage. A tropical IPA can lose much of its mango within weeks if it sits warm, leaving a dull, sweetish beer.

That is why freshness matters so much for hoppy beer in India. Our guide to fresh versus stale IPA explains how to tell. Cold storage from brewery to glass makes a huge difference.

Hops themselves fade too. Brewers store pellets in sealed, oxygen-free foil packs in a freezer or cold room and use an opened pack quickly. A bag of hops left open on a warm brewhouse shelf in Bengaluru starts to smell cheesy within weeks, a sign the oils and acids have oxidised.

Training your nose

Smelling hops directly is the best way to learn. Rub a pellet or two between your palms and sniff. Try a few varieties side by side and you will soon tell pine from citrus from tropical fruit. Then smell a beer brewed with one of them and see how much of that character made it through the brewhouse.

Matching those smells to the hop and the brewing step behind them is the next level. It takes structured comparison of styles brewed with different hops, which is the kind of work a style course is built around.