At the end of cold conditioning, the beer is only lightly carbonated — about 1.0 to 1.5 g of CO₂/L. But in Belgium we like our beers nicely fizzy, around 5.0 to 6.0 g of CO₂/L. The traditional method bridges the gap by creating 4.0 to 5.0 g of CO₂/L directly in the bottle. The principle: add a sugar syrup and a specific yeast to build the carbonation.
Calculating the amount of sugar
You get 1.0 g of CO₂/L by adding 2.0 g of sugar/L. The amount of sugar to add therefore sits between 8.0 and 10.0 g/L: the more fizz you want, the higher the dose.
Important: before bottling, make sure fermentation is fully finished and the final gravity is reached. Otherwise the residual sugars would turn into CO₂ as well and give excessive fizz. (See the appendix at the end of the article to calculate the final gravity.)
The bottling steps
Preparation and transfer
- Sanitise the transfer equipment (auto-siphon, bottling wand), the mixing keg and the bottles with a Star San solution.
- Transfer the beer from the conditioning keg to the mixing keg with the auto-siphon, leaving the yeast sediment behind in the conditioning tank.
The sugar syrup
- In a saucepan, mix equal parts sugar (for the total volume of beer) and drinking water.
- Heat to 85 °C, stirring constantly, then stop and let it cool a little.
- Pour gently into the mixing keg using a funnel.
The yeast (for 20-25 L)
- In a sanitised vial, rehydrate 1.0 g of Fermentis F-2 dry yeast in 50 ml of sterile water at 25 °C.
- Pour gently into the mixing keg.
Bottling and storage
- Fill the bottles with the bottling wand. During filling, stir the beer occasionally to keep the F-2 yeast in suspension.
- Cap them (swing-top bottles are an economical alternative).
- Store the bottles upright, away from light, somewhere temperate (between 21 and 25 °C) for 2 weeks.
- After 2 weeks, chill a bottle and taste to check the carbonation. If it’s good, move everything somewhere cool (12-15 °C); if it’s a touch flat, leave it another week at room temperature.
Storage and tasting
- To preserve their hop aromas, IPAs are best kept cold.
- Strong beers can age several years in the cellar: oxidation notes develop and add complexity.
- Thanks to the yeast present, the flavour evolves over time. Some styles, like the Triple, deserve 4 to 5 months of cellar maturation to reach their peak.
Appendix — calculating the apparent final gravity
Attenuation expresses the percentage of sugar turned into alcohol and CO₂ by the yeast (a figure provided with each yeast, generally between 65% and 90%). It’s an apparent value: since the beer contains alcohol, which is less dense than water, the real attenuation is lower.
The difference between the original extract and the apparent extract gives the apparent attenuation. Knowing the original extract and the attenuation:
A.E. = O.E. × (1 − Att)
Example: O.E. = 10 °Plato, attenuation = 80% (0.8) → A.E. = 10 × (1 − 0.8) = 2 °Plato.
With a hydrometer graduated in relative density:
F.G. = ((O.G. − 1) × (1 − Att)) + 1
Example: O.G. = 1.040, attenuation = 80% → F.G. = ((1.040 − 1) × (1 − 0.8)) + 1 = 1.008.
For the correct use of the hydrometer, see “How to use a hydrometer”.
