How fill level in a tasting glass changes the aroma you get

Aroma lives in the headspace

Aroma compounds leave the beer's surface and collect in the air above it, inside the bowl of the glass. That pocket of air is the headspace. When you sniff, you draw air from the headspace into your nose. The more concentrated the aroma there, the more you smell.

A glass filled to the top has almost no headspace. Aroma escapes straight into the room. A glass filled a third or half way has a deep pocket of air that holds aroma and channels it towards your nose.

How much to pour

For tasting rather than drinking, smaller pours work better:

• Tasting a flight: around 50 to 60 ml per beer is usual. Enough for a few sips and a second look.
• Tasting one beer properly: fill a tulip or wine glass to about a third of its capacity.
• Drinking: fill as you like, but taste the first sips from a partial pour if you want to appreciate the aroma.

Wine panels use a standard tasting glass of about 215 ml filled with around 50 ml for the same reason. Beer needs a bit more room for foam, but the principle is the same.

Leave room to swirl

A partly filled glass also lets you swirl. Swirling coats the inside of the bowl with a thin film of beer and breaks the surface, which releases a fresh burst of aroma into the headspace. A full glass cannot be swirled without spilling.

With a very fizzy beer, swirl gently. Too much movement knocks out CO2 and flattens the beer. Our guide on the right way to smell a beer covers how to combine swirling with short sniffs.

Glass shape works with fill level

Fill level and glass shape work together. A glass that narrows towards the rim, like a tulip, a snifter or a wine glass, traps aroma in the headspace and focuses it at the opening. A straight sided pint glass lets aroma spread out and escape, whatever the fill level.

The best tasting set-up is a narrowing glass filled about a third full. That gives you a deep headspace, room to swirl and a rim that funnels the aroma to your nose. A tulip glass costs little and changes a tasting far more than any expensive accessory. Our guide on setting up a beer tasting covers the rest of the table.

Foam takes up headspace too

The head on a beer is part of the fill. A tall, dense head sits in the space where aroma would otherwise gather. Some aroma compounds also cling to the bubbles. As the foam collapses, it releases a burst of aroma, which is why a beer often smells strongest a minute or two after pouring.

For tasting, aim for a modest head, perhaps one or two finger widths in a tulip glass. Pour down the side of the tilted glass, then straighten it towards the end. With wheat beers and Belgian ales that foam heavily, pour a little less beer to leave room. Wait for the head to settle slightly before your first sniff. Comparing two beers with very different heads is not a fair test of aroma, so match the foam as closely as you can.

Keep every glass the same in a comparison

If you are comparing beers, fill level is a hidden variable. A glass that is half full will smell stronger than one filled almost to the top, even if the two beers are identical. In a blind tasting or a panel, that difference can be mistaken for a real difference between beers.

So use identical glasses and pour the same volume into each. A small measuring jug or a mark on the glass makes this easy. Pour gently and keep the foam similar too, because a thick head changes how much aroma escapes.

Temperature and time in the glass

Fill level interacts with temperature. A small pour warms faster than a full glass, especially in Indian summer heat. Warming releases more aroma, which helps at first. Leave it too long and the beer goes warm and flat. Pour small, taste fairly soon and pour again rather than leaving a sample sitting for twenty minutes.

Cover the glass with your hand or a coaster for half a minute before sniffing to build up aroma in the headspace. Judges use this trick to find faint notes. It works best in a partly filled glass.

Your first step

Pour the same beer into two identical wine glasses: one about a third full, the other almost to the brim. Smell each in turn with short sniffs. Write down what you get from each. Then swirl the third full glass and smell again. The difference is often bigger than people expect.

Common questions

How full should a beer tasting glass be?

About a third full in a tulip or wine glass is ideal for tasting. For a flight, 50 to 60 ml per beer is common.

Why does a less full glass smell stronger?

The empty space above the beer, the headspace, collects aroma before it reaches your nose. A full glass has almost no headspace, so aroma escapes into the room.

Does glass shape matter as much as fill level?

They work together. A glass that narrows at the rim traps aroma, while a partial fill gives it space to gather. The best set-up uses both.