Bottling your beer: priming and conditioning

When to bottle

Only when fermentation is finished: the gravity must be the same two to three days in a row, close to the expected final gravity. Bottling a beer that is still fermenting adds sugar to what remains: the pressure rises beyond what the bottle can take. The fermentation guide explains how to check it.

Preparing the bottles

• Crown-cap beer bottles (thick glass, preferably brown) or swing-top bottles. Never soda or wine bottles not designed for pressure.
• Rinse each bottle right after drinking it: a dried deposit takes much longer to remove.
• On bottling day, sanitise bottles, caps, bucket and bottling wand. For a sanitiser such as Star San, allow 1.5 to 2.5 mL per litre of water (cleaner and sanitiser dosage).
• For 20 litres, prepare 59 bottles of 33 cl, or 39 of 50 cl; the number of bottles calculator works it out for your volume.

How much sugar

The dose depends on the carbonation you want, expressed in volumes of CO2, and on the highest temperature the beer reached after fermentation: a beer that stayed cold has kept more gas and needs less sugar.

• For 2.5 volumes, the carbonation of a blonde or an American ale, and a beer kept at 20 °C: 6.4 g of table sugar per litre, about 128 g for 20 litres (priming sugar calculator).
• With dextrose, you need a little more: 7.1 g per litre, 141 g for 20 litres. Honey and malt extract have their own doses (priming by sugar type).
• Each style has its range: an English bitter is served lightly carbonated, a weizen or a saison very sparkling (carbonation by style).

Do not go above 4 volumes in ordinary bottles: beyond that, they can burst. Weigh the sugar, do not measure it by the spoonful.

Priming the whole batch or bottle by bottle

• The whole batch: dissolve the sugar in a little boiled water (200 to 300 mL), pour this cooled syrup into the bottom of a sanitised bottling bucket, then siphon the beer onto it without splashing. The sugar spreads evenly into every bottle. This is the most accurate method.
• Bottle by bottle: a sugar cube, a carbonation drop or a measured dose in each bottle. Handy without a bucket, but less even, and riskier with bottles of different sizes.

Filling and capping

Fill from the bottom with a spring-valve bottling wand, right to the top: when you withdraw the wand, 2 to 3 cm of air is left under the cap. Cap straight away. Leave the yeast sediment at the bottom of the fermenter.

Conditioning

• Two weeks at 18-22 °C for carbonation. Below 15 °C, it can take a month or more.
• Then somewhere cool, upright, away from light: the yeast settles at the bottom of the bottle.
• Open a bottle after a week to follow the carbonation. A beer that is still flat after three weeks somewhere warm lacks sugar or yeast.
• When serving, pour gently, leaving the last centimetre and its sediment in the bottle.

Light, hoppy beers are drunk young, within two months; strong, dark beers often improve over several months.

What about a keg?

In a keg, you can prime the same way (with a little less sugar) or carbonate with CO2 from a gas bottle: cold beer absorbs the gas under pressure. For 2.5 volumes at 4 °C, you need 0.83 bar (carbonation pressure). A keg saves washing sixty bottles, at the cost of a regulator, a CO2 bottle and space in the fridge.

Common mistakes

• Bottling just because the airlock has stopped, without measuring the gravity: this is the main cause of bottles that gush or explode.
• Measuring the sugar by volume rather than by weight.
• Forgetting to stir gently after pouring the beer onto the syrup, when the transfer was not enough to mix it: the first bottles are flat, the last ones overcarbonated.
• Storing the bottles somewhere cold from the next day: the yeast goes dormant before it has carbonated the beer.