Why your first homebrew tastes thin or a little like cider

Cause one: too much plain sugar

Many starter kits tell you to add a kilo of table sugar to a can of malt extract. Sugar ferments completely. It adds alcohol but no body, no malt flavour and no protein to carry the foam. When a large share of the fermentable material is plain sugar, the result is thin, dry and a little winey.

Brewers have a name for the character: "cidery". It is one of the most common first batch complaints.

The fix: replace the sugar with more malt extract, either liquid or dry. If you are brewing all-grain, keep simple sugars under about 10 to 15% of the fermentables unless the style calls for more, as in some Belgian ales.

Cause two: fermenting too warm

Yeast does most of the flavour work in beer. Heat changes what it produces. Above the strain's preferred range, ale yeast makes more fruity esters and harsher fusel alcohols. Some of those esters taste like apple or pear.

This is the most Indian of the four causes. A fermenter left in a living room in Hyderabad in April can sit at 30 °C. The liquid inside gets warmer still, because active fermentation produces its own heat. A beer that "fermented at room temperature" may have spent its first two days at 32 °C or more.

The fix: control temperature. A fridge with a controller is best. Failing that, stand the fermenter in a tub of water with a wet towel wrapped round it and frozen water bottles swapped in morning and evening. Aim for 18 to 20 °C for most ale yeasts, particularly in the first three days.

Cause three: the beer is not finished

Green apple is also the signature of acetaldehyde, a compound yeast makes on its way to producing alcohol. Healthy yeast reabsorbs it near the end of fermentation. If you bottle too early or stress the yeast so it gives up, acetaldehyde stays behind.

The fix: wait. Bottle only when two hydrometer readings a few days apart match. Then leave the bottles to condition for at least two weeks before you judge. Our guide to the acetaldehyde off flavour explains how to tell green apple from the other fruity notes.

Cause four: the mash was too cool

If you brewed all-grain and the beer is thin and very dry rather than appley, look at your mash temperature. Enzymes in the mash break starch into sugars. At 62 to 64 °C they make mostly sugars that yeast can ferment, leaving a dry, light bodied beer. At 67 to 69 °C they leave more sugars the yeast cannot ferment, giving a fuller, sweeter beer.

A cheap dial thermometer that reads 3 °C high will push every mash cooler than you think. Check yours in boiling water and in ice water before brew day. Our mash temperature guide covers the ranges for different styles.

How to tell which cause you have

Taste with the four causes in mind:

• Thin, dry, winey, low foam: too much sugar or a cool mash.
• Fresh green apple, fades over a few weeks in the bottle: young beer, acetaldehyde.
• Pear, banana or solvent with a hot alcohol edge: fermentation too warm.
• Sharp sourness or vinegar: that is different. It points to bacteria, which means sanitation.

Look at your numbers too. A beer that finished at 1.004 from a kit with a kilo of sugar is telling you where its body went.

Your second batch

Change one thing at a time so you learn what fixed it. If you used sugar, swap it for malt. If you fermented warm, cool it. Keep notes on gravity, temperature and dates. If you brewed from a kit, a good next step is a recipe made entirely from malt extract with a short steep of specialty grain, which adds body and colour with no extra equipment. Our list of common first homebrew mistakes has the other usual suspects.

What most beginners lack is not a better recipe but a picture of what is happening inside the fermenter and why. Once you have that, you stop fixing beers after the fact and start brewing them right the first time.