The beer clean glass test and why bubbles stick to dirty glasses

What beer clean means

A beer clean glass is free of grease, detergent residue, lint and anything else that interferes with foam and carbonation. It looks no different from an ordinary clean glass. The difference shows only when beer goes in.

Glasses that are fine for water or soft drinks often fail with beer. Beer foam is held together by proteins and hop compounds. A thin film of fat or detergent breaks it apart. That is why bars that serve good beer treat glass washing as part of quality control, not housekeeping.

Why bubbles stick to dirty glasses

Carbon dioxide dissolved in beer needs somewhere to form a bubble. In a perfectly clean, smooth glass there are few such places, so bubbles rise mainly from the bottom or from deliberate etching. Residue on the glass, whether grease, dried detergent, a fibre from a towel or a speck of dust, gives the gas a rough spot to collect on. Bubbles form there and cling to the side instead of rising.

That has three costs. The beer loses carbonation faster and tastes flat. The head collapses because fat and detergent destroy foam. And the guest sees a glass that looks neglected. Our guide to beer foam science explains why foam is so sensitive.

Test 1: the sheeting test

Dip the glass in clean water and lift it out. On a beer clean glass the water sheets off in an even, unbroken film. On a dirty glass the water breaks into droplets or leaves dry patches where grease repels it. It takes five seconds and needs no equipment.

Test 2: the salt test

Wet the inside of the glass and sprinkle salt over it. On a clean glass the salt sticks evenly over the whole surface. Where there is a film of grease, salt will not stick and you see bare patches. It is a good way to show staff exactly where the residue is, often around the rim where lips and lipstick touch.

Test 3: the lacing test

Pour a beer and drink it in several sips. On a clean glass the foam leaves rings of lace on the inside, one for each sip. On a dirty glass the foam slides down without leaving lace, or leaves patchy marks. This is the test guests see, so it is the one that matters most. It also depends on the beer, since some styles naturally lace less than others.

A washing routine that works

• Keep beer glasses separate. Do not wash them with greasy plates, milk jugs or cocktail glasses with cream.
• Use a detergent made for glass, at the dose on the label. Too much leaves a residue that kills foam.
• Follow the three-sink order if washing by hand: wash with a brush, rinse in clean water, then sanitise. Change the water often.
• Rinse well in cold water before use.
• Air-dry upside down on a rack that lets air move. Never dry with a towel, which leaves lint and grease.
• Do not store glasses in a freezer or a fridge with food. They pick up smells and ice ruins the pour.
• Service your glass washer. Check water temperature, detergent and rinse aid levels on a schedule.

Common culprits behind dirty glasses

When glasses keep failing, the cause is usually one of a short list. Lipstick and lip balm are oily and survive weak washes. Milk, cream and butter from coffee or dessert service leave fat. Glass washers with the wrong detergent, a blocked rinse arm or water that is not hot enough leave a film. Hard borewell water can leave mineral spots that look like dirt and give bubbles somewhere to form. Towel drying adds lint every time.

Fix the cause, not the glass. Rewashing a failed glass in the same machine with the same detergent rarely helps.

Make it part of quality control

Run the sheeting test on a few glasses at the start of every shift and the lacing test on the first pour of each tap. Keep a simple log. When foam complaints come in, the log tells you whether the problem is the glass, the draught lines or the beer. A glass rinser at the tap helps too: a quick cold rinse just before pouring cools the glass, removes dust and gives the beer a better start. Our guide to how to pour beer covers the pour itself.

Clean glass is the easy part. The harder part is training a team to see a flat head or a dull aroma and know whether the glass, the line or the beer caused it. That needs a trained palate behind the bar.

Common questions

Why do bubbles stick to the side of my glass?

Bubbles form on residue such as grease, detergent or lint. On a clean glass they rise from the bottom instead of clinging to the sides.

How do I test if a glass is beer clean?

Dip it in water and watch the water sheet off evenly, sprinkle salt on a wet glass to see whether it sticks everywhere or check that foam leaves rings of lace as you drink.

Should beer glasses be dried with a towel?

No. Towels leave lint and grease. Air-dry glasses upside down on a rack that lets air circulate.

Is a frozen glass good for beer?

No. Ice on the glass makes beer foam and lose carbonation, numbs flavour and the glass can pick up freezer smells.