Tasting wort and green beer to catch problems early

Why taste so early

Finished beer tells you something went wrong. Wort and green beer tell you when. A brewer who tastes at every stage builds a mental map of how each beer should develop, so a deviation stands out on the day it happens rather than at packaging.

Tasting early is cheap. A sample costs a few millilitres and a minute. A dumped tank costs the whole batch, the tank time and the slot in your production plan.

Tasting wort on brew day

Taste first wort from the lauter tun, the last runnings and the kettle at knockout. Cool every sample before tasting it. Hot wort burns and hides flavour.

• First wort. Should be very sweet, bready and clean. Unless the recipe uses acidulated malt, a sour or vinegary note usually means bacteria in the mash tun.
• Last runnings. Thin and less sweet is normal. A harsh, drying, tea-like grip is astringency from husk tannins, usually from oversparging, sparge water that is too hot or a mash pH that drifted high. Check gravity and pH alongside taste.
• Kettle at knockout. Should taste sweet and properly bitter for the recipe. A burnt, acrid note means scorching on the kettle element or jacket.
• Cooled wort before pitching. Smell it for cooked sweetcorn. Strong DMS here means the boil was too weak or the wort sat hot too long before cooling.

Tasting green beer through fermentation

Green beer is beer that has fermented but not yet matured. It is supposed to taste rough. The point is to know what normal rough looks like for each brand on each day, so abnormal stands out.

Take a sample at the same time each day when you read gravity and temperature. Note what you find against the fermentation curve.

• Sulphur. Rotten egg or struck match in the first days of a lager is normal and should fade as fermentation slows. If it persists late, look at yeast health. See sulphur in lager fermentation.
• Acetaldehyde. Green apple. Expected mid-fermentation. Should be gone before the beer leaves the fermenter.
• Diacetyl. Butter or butterscotch. Expected to rise and then fall. It must be gone before you cool the tank.
• Sourness, vinegar or a ropy texture. Never normal in a clean beer. Plate a sample and check your cleaning records.

The forced diacetyl test

Tasting green beer for diacetyl has a catch. Much of it is still present as a precursor, alpha-acetolactate, which has no flavour yet but will turn into diacetyl later, sometimes in the package. A beer can taste clean today and buttery next month.

The forced test exposes it. Take two sealed samples. Hold one at around 60 to 70 °C in a water bath for 10 to 20 minutes, then cool it to the same temperature as the control. Smell both. If the heated sample smells of butter and the control does not, precursor is still in the beer and the tank is not ready for cooling. Keep it warm until both samples smell clean. Our guide to the diacetyl rest covers the temperatures.

Sampling without contaminating the tank

A sample valve is a direct route into the beer. Spray it with 70% ethanol or your sanitiser before opening it, run a little beer to waste to flush the valve and sanitise again after closing. Sample into a clean glass, not a cup that sat on the floor. Never return a sample to the tank.

What to record for each tasting

A tasting note is only useful if someone can compare it with the next one. Keep it short and structured:

• Date, time, tank and brand.
• Gravity, temperature and pH at the moment of sampling.
• Aroma notes with an intensity from 0 to 5 for each.
• Any flavour or mouthfeel notes.
• An action, even if the action is "none, on track".
• Initials of each taster.

Use the same list of words for every beer so trends show up. If one taster writes "buttery" and another writes "rich" for the same sample, agree which word you will use and why. Over time those records become one of the most valuable documents in the brewery.

Make it a routine

Write down what you taste on the same brew sheet as gravity, temperature and pH, using the same words every day. Have two people taste where possible. Spit rather than swallow: you may taste a dozen samples in a shift. After a few months the records become a reference library for each brand. A new assistant brewer can learn from them.

The limit of all this is your own calibration. If you have never tasted diacetyl at a known level, you will miss it at low levels or call it something else. Spiked samples and panel training fix that.

Common questions

Is sulphur in young lager a fault?

Not early in fermentation. Many lager strains produce sulphur that fades as fermentation finishes and the beer matures. It is a problem only if it persists into conditioning.

How do I run a forced diacetyl test?

Heat one sealed sample of green beer to around 60 to 70 °C for 10 to 20 minutes, cool it and smell it beside an unheated sample. Butter in the heated sample means precursor remains.

Should I swallow when tasting fermentation samples?

No. Spit. You may taste many samples in a day and need your palate and judgement intact.

What does astringency in wort taste like?

A dry, puckering, tea-like grip rather than a flavour. It usually comes from oversparging, hot sparge water or a high mash pH.