Brewing a batch that tastes the way you meant

Every brewer is after a pint that tastes the way they planned it.

A few steady habits do much of the work. When a batch does taste odd, the taste or smell usually gives a strong clue to what happened. These notes go from that clue to its likely causes, and to what brewers change for the next batch.

Habits behind a good batch

Many off-flavours share the same few remedies. Brewers keep their kit clean and sanitised. They pitch enough healthy yeast into well-aerated wort. They keep the fermentation temperature under control and let the fermentation finish before moving the beer.

Writing down each batch's temperatures and timings makes any fault easier to trace.

Start with the beer you meant to make

Beer judges allow several off-flavours in small amounts in certain styles. A light butter note can suit a bitter or a Czech lager. Sourness is part of a Berliner Weisse or a lambic.

So it helps to start with the beer you meant to make.

Reading flavours from the fermentation

• Green apple or cider. This is acetaldehyde. It usually means the beer is young, or it came off the yeast before fermentation finished. A longer, complete fermentation tends to clear it.
• Butter or butterscotch. This is diacetyl. Stressed yeast is the most common cause. Moving the beer off the yeast, or chilling it, too early can leave it behind. It can also point to bacteria or to dirty keg lines.
• Hot, solvent or nail varnish remover. High fermentation temperatures, too little yeast and too little oxygen in the wort are the usual causes. A wild yeast can do it too.

Reading flavours from brew day

• Cooked corn or cabbage. This is dimethyl sulfide. Pale malts carry a compound that turns into it with heat. An open, rolling boil drives it off. Covering the kettle or cooling the wort slowly overnight lets it stay.
• Sticking plaster or medicine. Chlorine is a common cause. It can come from tap water, or from a chlorine sanitiser that was not rinsed well. Wild yeast can give a similar taste.

Keeping beer fresh after packaging

• Wet cardboard or stale bread. This is oxidation. Splashing the beer when it is moved or bottled lets air in. Warm storage and age make it worse.
• Skunky. Light reacts with the hop compounds in beer. Clear and green bottles let it through. Brown bottles kept out of the sun protect the beer.

If a batch has picked up an infection

Brewing scientists trace most spoilage in European breweries to four groups of bacteria. They are Lactobacillus, Pediococcus, Pectinatus and Megasphaera.

• Sour or vinegary. Acid-making bacteria are the usual cause. A scratched plastic fermenter is one known cause.
• Thick, ropy or slimy. Some strains of Pediococcus make the beer gelatinous. The same bacteria can also bring a buttery taste.
• Rotten eggs, with a heavy haze. Pectinatus and Megasphaera both make beer cloudy and give it a smell of rotten eggs.
• Bottles that gush or burst. A yeast called diastaticus can break down the starches and dextrins left in finished beer. The extra fermentation makes too much gas in the bottle.

Useful links

• Troubleshooting off-flavours, a set of cards from the Minnesota Home Brewers Association, published by the BJCP (PDF)
• American Homebrewers Association: acceptable off-flavors in beer and homebrew
• Beer Judge Certification Program, which publishes the beer style guidelines
• Microbiological instability of beer caused by spoilage bacteria, a review in the Journal of the Institute of Brewing (PDF)
• Understanding the beer spoilage yeast diastaticus, a study from Chalmers University of Technology
• Chartered Institute of Brewers and Distillers