Brewing an imperial stout at home and waiting for it

Imperial stout is a high gravity project

The style is broad. Original gravity runs from about 1.075 to 1.115, final gravity 1.018 to 1.030, bitterness 50 to 90 IBU and strength 8 to 12% ABV. Flavours range from dark chocolate and coffee to dried fruit and treacle. All of it rests on a fermentation that finishes properly.

Start with a smaller batch. A 10 litre imperial stout ties up less grain and the waiting costs you less fermenter space. If you have not brewed a standard stout yet, our stout guide is the place to start.

A grist for 10 litres

For 10 litres at about 1.095, assuming efficiency falls to around 65% with this much grain:

• 4.0 kg pale ale malt (77%)
• 0.35 kg roasted barley (7%)
• 0.3 kg chocolate malt (6%)
• 0.3 kg medium crystal malt (6%)
• 0.2 kg flaked oats (4%)
• Mash at 65 to 66 °C for 75 minutes

Keep the mash fermentable. Roasted malts and crystal leave plenty of body already. A hot mash on top gives you a beer that stalls at 1.040 and tastes like syrup. If your mash tun is small, top up the gravity with about 0.5 kg of light dried malt extract in the boil.

Bitterness has to fight the sweetness

Aim for around 60 IBU. In 10 litres that is roughly 30 g of a 12% alpha bittering hop at 60 minutes. Calculated IBUs read high in strong worts because hop utilisation falls as gravity rises, so the beer will taste less bitter than the number suggests. Boil 90 minutes to concentrate the wort and darken it a little further.

Pitch big and give it oxygen

This is where most homebrewed imperial stouts fail. Yeast faces high sugar at the start and high alcohol at the end. Give it numbers and oxygen:

• Two sachets of a clean, alcohol-tolerant dry ale yeast for 10 litres, rehydrated, or a large starter
• Pure oxygen through a stone for 60 seconds, or vigorous shaking for several minutes
• Yeast nutrient in the last 10 minutes of the boil

Pitch at 17 °C and hold it there for three days. The fermentation will generate a lot of heat. Then let it rise to 20 to 21 °C so the yeast can finish. Our guide to brewing a 10% beer without stalling goes deeper into high gravity yeast care.

Waiting is part of the recipe

Leave the beer in the fermenter for three to four weeks. Package only when gravity has stayed the same for a week. For bottles, add fresh yeast at bottling: the original yeast is tired after 10% alcohol and may not carbonate the bottles. Aim for a modest 2.0 to 2.3 volumes of CO2.

Then wait. Most imperial stouts taste hot and disjointed at one month, rounder at three and properly integrated at six. Taste one bottle at each mark and write down what you find.

Store it cool in an Indian climate

Heat speeds up staling. A stout kept at 32 °C on a shelf will move through its best window far faster than one stored at 15 to 18 °C. In big dark beers, slow oxidation can bring pleasant sherry and dried fruit notes, but heat turns them to cardboard. Keep bottles dark, upright and as cool as your home allows. A wine fridge or the bottom of a cupboard against an inside wall is better than the kitchen.

Adding coffee, vanilla or oak later

Many brewers split an imperial stout into variants. The base beer has to be finished before you add anything, otherwise you cannot tell whether a flavour came from fermentation or from the addition. Draw off a litre or two into a sanitised container, add the extra and taste daily.

• Coffee: cold brew concentrate added at packaging, dosed to taste. Our coffee stout guide covers the method.
• Vanilla: one split pod per 5 litres for about a week, checked often.
• Oak: 10 to 15 g of medium toast oak cubes per 5 litres, soaked first in a little spirit to sanitise them, for two to six weeks.

Taste every few days. It is easy to add more of anything and impossible to take it out. Keep a plain portion of the base beer as a control so you can judge what the additions really did.

Measure the mash tun before you buy grain

Check how much grain your mash tun can actually hold before you buy any. Fill it with water to the brim, note the volume and allow about 3.5 litres of mash per kilogram of grain. If 5.2 kg will not fit, plan the extract top-up now.

Common questions

How long should an imperial stout age?

Most taste noticeably better at three months and are well integrated by six. Taste one bottle at each stage.

Do I need to add yeast at bottling?

For bottle conditioning a beer around 10% ABV, yes. Fresh, alcohol-tolerant yeast carbonates more reliably than the tired original yeast.

Why did my imperial stout stall?

The usual causes are underpitching, too little oxygen or a mash that ran too hot and left unfermentable wort.

What temperature should I store it at?

As cool and steady as you can manage, ideally 15 to 18 °C and away from light.