Hop Glossary: What Is IBU? Alpha Acid, Dry Hopping & Hop Terms Explained

From alpha acid percentages to dry vs. wet hopping, hop terminology can get technical fast. This glossary breaks down the terms you'll see on our hop listings and in recipes. For a full side-by-side comparison of varieties by alpha acid, type and flavour, see our Hops Selector.

What Is IBU?

IBU (International Bitterness Units) is a scale measuring the perceived bitterness contributed by hop-derived compounds dissolved in beer, roughly 0–100+. A light lager might sit around 8–12 IBU, an English bitter 20–35, and a West Coast IPA 60–100+. IBU is a lab measurement of bitterness, not a direct measure of hop aroma or flavour — a beer can be high-IBU but low on hop aroma, or the reverse.

Alpha Acid (%)

Alpha acid percentage is the single biggest driver of a hop's bittering potential. Higher alpha acid varieties (Target, Chinook) need less weight to hit a target IBU and are typically used for the long boil (bittering) addition. Lower alpha acid varieties (Saaz, Tettnanger) are usually chosen more for flavour and aroma than pure bittering power.

Beta Acid (%)

Beta acids contribute little bitterness during the boil (they don't isomerise the way alpha acids do) but oxidise over time in storage, which is part of why hops lose potency and develop "cheesy" off-notes if stored too long or too warm. Freezing hops in sealed packaging slows this degradation significantly.

Cohumulone

Cohumulone is a sub-type of alpha acid. Hops higher in cohumulone (many high-alpha bittering varieties) are sometimes associated with a harsher, coarser bitterness, while lower-cohumulone varieties are generally considered smoother — though this is debated among brewers and the effect is subtle in practice.

Dry Hopping

Dry hopping means adding hops after the boil — typically during or after fermentation, at room temperature or slightly warmer — to extract aroma and flavour oils without adding bitterness (since there's no boiling to isomerise the alpha acids). It's the technique behind the big, juicy hop aroma in modern IPAs and pale ales.

Wet Hopping

Wet hopping uses fresh, undried hops straight from the bines rather than the dried pellets or whole leaf most home brewers use year-round. It gives a brighter, greener, more "fresh-cut grass" character but is only possible for a short window around harvest (typically September in the UK) since fresh hops spoil quickly.

First Wort Hopping

First wort hopping means adding a hop charge to the kettle before the boil even starts, as the wort is running in from the mash. It gives a smoother, more refined bitterness than a standard 60-minute boil addition, though the effect is subtle and debated.

Hop Schedule

A hop schedule is the full plan of hop additions for a brew — what variety, how much, and at what point (60 min, 20 min, flameout, dry hop) for each. Building a good schedule means matching each hop's alpha acid and flavour profile to the role you want it to play: bittering, flavour, or aroma.

Bittering vs. Aroma Hops

Hops are broadly grouped as bittering (high alpha acid, added early for IBU), aroma (lower alpha acid, added late or dry-hopped for smell/taste), or dual-purpose (good at both). Our Hops Selector lets you filter by all three.

Hop Pellets vs. Whole Leaf

Pellets are compressed, ground hops — more efficient (less oxygen exposure, higher utilisation, easier to store and dose precisely) and what most home brewers use. Whole leaf (or "whole cone") hops are less processed, can give a slightly different character, but take up more space in the kettle/fermenter and are harder to dose exactly.

Frequently Asked Questions

What is a good IBU for a beginner homebrew?

Most classic styles sit in the 20–40 IBU range — bitters, milds and pale ales. Save very high-IBU IPAs (60+) for once you're comfortable with your process, since bitterness can mask other process issues.

Does dry hopping add bitterness?

Very little. Because there's no boiling involved, the alpha acids aren't isomerised into bitter compounds — dry hopping is almost entirely about aroma and flavour, not IBU.

What's the difference between alpha acid and IBU?

Alpha acid % is a property of the raw hop. IBU is the resulting bitterness measured in the finished beer, which depends on alpha acid %, hop quantity, boil time, wort gravity, and other factors.

How should I store hops to protect alpha acid?

Keep hops sealed, cold, and away from light — ideally in the freezer. Alpha and beta acids degrade steadily at room temperature.