Bottle conditioning in hot weather without gushers

How bottle conditioning works

You add a measured amount of sugar to finished beer, bottle it and cap it. The yeast still in the beer ferments the sugar. Because the bottle is sealed, the CO2 dissolves into the beer. About 6 to 8 g of table sugar per litre gives the usual level of carbonation for most ales, around 2.2 to 2.5 volumes of CO2. Weigh the sugar, do not guess. Dissolve it in a little boiled water, mix it gently into the beer in the bottling bucket and bottle.

Heat changes the timing more than the sums

At 18 to 20 °C, bottles take two to three weeks to carbonate. At 25 to 30 °C, they can be ready in about a week. The warmth also means the yeast works faster, so if there is any unfermented sugar left, the pressure rises quickly. The priming sum changes only a little. Beer that fermented warm holds less dissolved CO2 to begin with, so it needs slightly more sugar for the same result. A priming calculator that asks for the highest temperature the beer reached handles this.

Make sure fermentation is truly finished

The main cause of gushers and burst bottles is bottling beer that was not finished. Take a hydrometer reading, wait two days and take another. If the numbers match, bottle. If they fall, wait. Heat speeds fermentation, but it can also make yeast stall at high gravity, so do not trust the airlock.

Other causes of gushers

Over-priming, when too much sugar is added or the beer already holds sugar from fruit, produces too much pressure. Infection with wild yeasts that eat dextrins which brewer's yeast leaves behind (Saccharomyces diastaticus is one) causes a slow, steady rise in pressure over weeks and the beer turns dry and thin. Dirty bottles or poor sanitation lead to the same. If bottles keep gushing on a batch you primed correctly, suspect infection and see homebrewing in the humid tropics for sanitation habits.

Choose strong bottles

Use bottles made for beer, with thick glass and a crown cap. Do not reuse bottles with chips, cracks or thin walls. Avoid wine, spirit and novelty bottles too. PET soda bottles are a useful alternative: you can squeeze one to feel the pressure and they do not shatter. Fill one PET bottle as a test in each batch. When it feels as hard as a tyre, the glass bottles are carbonated.

Store safely, then chill

Keep bottles in a closed box or a plastic crate with a lid, away from where people sit, so that a failure does no harm. Do not leave bottles in direct sun or in a car. When carbonated, move them to the fridge or the coldest place you have. Cold stops the yeast, drops the pressure and helps the CO2 dissolve. A gusher opened warm will foam, so chill all bottles for a day or two before opening. Our related guide converting brewing recipes includes the pressure and carbonation units.

A worked priming example

Say you have 18 L of finished beer and want about 2.4 volumes of CO2. At roughly 7 g of table sugar per litre, that is 126 g. Weigh it on a scale to the nearest gram, dissolve it in 250 ml of boiled water, cool it and stir it gently into the beer in the bottling bucket. Bottle the lot within the hour.

Write the date on a label. Test a PET bottle after five days. If it is firm, move one glass bottle to the fridge for 24 hours and open it. If the carbonation is right, chill the rest. If it is flat, wait three more days and test again.

An alternative: kegging

If bottles in the heat worry you, a small keg (a 5 L mini keg or a 19 L cornelius keg) with a CO2 regulator gives controlled pressure and no priming sugar. It needs cold storage for best results, so it is not for everyone. Bottles with care remain the common choice for homebrewers in the tropics. See also homebrewing in Singapore and Malaysia and learning to brew online.

Common questions

How much priming sugar do I need?

About 6 to 8 g of table sugar per litre for most ales. Use a calculator and weigh it.

How long does bottle conditioning take in hot weather?

Often about a week at 25 to 30 °C, against two to three weeks at 18 to 20 °C.

Why do my bottles gush?

Usually because fermentation was not finished, too much sugar was added or an infection ate extra sugar. Check gravity and sanitation.

Should I refrigerate bottles?

Yes, once carbonated. It stops the yeast, reduces pressure and prevents foaming on opening.