Answering technical brewing questions at interview

What interviewers are testing

A technical question is rarely about the fact. It is about whether you understand the cause. If you can say what happens and why, you can usually work out the next question on your own.

A good answer has three parts: what happens, what causes it and what you would do about it. Keep each answer short. Give a number where there is one, say when you are unsure and ask a clarifying question if the question is open. Pair this with the advice in our guide to the brewer's CV and interview, which covers the rest of the process.

Mashing and the grain side

"What does mash temperature do?" Mash temperature decides which enzymes work fastest. Beta amylase makes fermentable sugar and works best around 62 to 65 °C. Alpha amylase makes longer, less fermentable chains and works best around 68 to 72 °C. A lower mash gives a drier, more fermentable wort. A higher mash gives a fuller body and a sweeter finish.

"What pH should the mash be?" About 5.2 to 5.6 measured at room temperature. Below that the enzymes slow. Above it you extract more tannin and the beer turns harsh. Mention that water chemistry and dark malts change pH. Say you would measure it and adjust.

"Why do we sparge and what can go wrong?" We rinse sugars out of the grain bed. Sparging too hot or too long pulls tannin from the husk and gives astringency. Stop collecting before the last runnings get thin and the pH climbs.

Boil, wort and fermentation

"Why do we boil for 60 minutes or more?" To isomerise hop alpha acids for bitterness, to sterilise the wort, to stop enzymes, to drive off volatile compounds such as DMS and to coagulate proteins. A vigorous open boil matters. Mention it.

"How do you calculate ABV?" ABV is roughly (OG minus FG) multiplied by 131.25. An OG of 1.050 and an FG of 1.010 gives about 5.25%.

"What is a sensible pitching rate?" A common guide is about 0.75 million cells per millilitre per degree Plato for ales and about 1.5 million for lagers. Under-pitching stresses the yeast and gives off flavours. Over-pitching can strip out ester character and leave a bland beer.

"What temperature do you ferment at?" Most ales sit around 18 to 22 °C. Lagers ferment cooler, around 8 to 13 °C. In a hot climate, say that temperature control is the first thing you would check.

Faults and how to trace them

Faults are favourite interview ground because they show reasoning.

• Diacetyl: buttery or butterscotch. Often the yeast was not given time to reabsorb it, or the beer was cooled too soon. A diacetyl rest at a slightly warmer temperature near the end of fermentation helps. Infection is the worse cause.
• DMS: cooked sweetcorn. From a weak boil, a lid left on or slow cooling after the boil.
• Acetaldehyde: green apple. The beer is not finished or the yeast gave up early.
• Oxidation: wet cardboard or sherry. Oxygen picked up after fermentation. Prevent it at transfer and packaging.

Our guide to beer off flavours covers these with causes and fixes. In the interview, always finish with the prevention step.

Cleaning, safety and quality

"How do you clean a fermenter?" Rinse, circulate a hot caustic cleaner, rinse again, then use an acid step if the plant calls for it, then sanitise just before use. Explain that cleaning removes soil and sanitising reduces microbes. Say you check results with a swab or a rinse test.

"What safety hazards matter most?" CO2 in confined spaces, hot liquids, caustic chemicals and moving packaging equipment. Never enter a tank without confined space procedures. Name two hazards and one control for each.

"How do you know a beer is ready to package?" It has reached final gravity and stayed there across readings, diacetyl is within spec, the sensory check passes and the yeast has settled. Say "I would taste it" and mean it.

The curveball and how to handle it

Sooner or later they ask something you do not know. Do not bluff. Say what you do know, work through it aloud and say how you would find the answer. For instance, if asked about a stuck sparge, you can reason through grain bed compaction, a fine crush or a high wheat share, then say what you would try first.

Be ready for questions about data too. Brewers increasingly record gravity, temperature and pH on screens. Our write-up of Ankur Napa's AI guide for brewers covers the AI side of that work. Interviewers like to hear that you know it exists.

Finish by asking a question of your own, such as which beers the brewery struggles with. It shows you care about the actual work.

Practise out loud

Reading answers is not the same as giving them. Say each one aloud, time it to under a minute and ask a friend to interrupt with "why?" at every step. If you stumble, the gap is in your understanding, not your delivery. Closing that gap is what a structured course is for.

Common questions

How technical are brewing interviews?

It depends on the role. A brewer role will ask about mashing, fermentation and faults. A quality or planning role may focus more on measurement and process.

Should I learn exact numbers for the interview?

Know the standard ones: mash pH 5.2 to 5.6, ale fermentation 18 to 22 °C, lager 8 to 13 °C and the ABV formula. Say when you are unsure.

What if I have no brewing job yet?

Talk about homebrew batches, courses and tastings. Show that you keep notes and learn from failures. Employers value the habit of measuring.

Is a brewing certificate useful at interview?

It shows you have covered the theory and practised under guidance. It supports your answers but does not replace hands-on experience.