Brew in a bag (BIAB): all grain in a single vessel

The principle

In a classic setup, you mash in one vessel, run off and sparge the spent grain into a second vessel, then boil. In BIAB, all the water for the batch is heated at once in the pot, the grain bag steeps in it for the length of the mash, and the bag, once lifted out, acts as the filter.

What this changes:

• A single vessel to heat, clean and store.
• A very thin mash (about 6 litres of water per kilo of grain, against 3 in a classic setup), which converts starch well.
• An efficiency a little lower than with sparging, around 65 to 75%: you make up for it with 5 to 10% more malt.
• A bag of 5 to 8 kg of wet spent grain to lift: a pulley or a rack laid on the pot helps a lot.

The equipment you need

• A pot of at least 35 litres for a 20 litre batch: it must hold all the water and the grain. 40 to 50 litres leave a margin against boil-overs.
• A filter bag in polyester voile, sized to the pot, strong enough to be lifted full.
• A heat source of 3 to 5 kW: gas burner (outdoors), compatible induction hob, or an electric element in the pot.
• A reliable thermometer, a lid, and insulation (blanket, insulating jacket) to hold the temperature during the mash.
• A wort chiller: copper or stainless steel immersion coil connected to the tap.

How much water for 20 litres

All the water goes into the pot from the start. For 20 litres (5.3 US gal) in the fermenter with 5 kg of grain, a one-hour boil and 3 litres evaporated per hour, the water volumes calculator in no-sparge mode gives:

The calculation counts 1 litre absorbed per kilo of grain. By squeezing the bag or letting it drain for a long time, you get down to 0.6 to 0.8 litre per kilo: note your real value after the first batch and enter it in the calculation.

Brew day, step by step

Heat the water

Heat all the water to mash temperature, a little above the target since the cold grain brings it down. As the mash is very thin, the difference is small: to hit 66 °C with 5 kg of grain at 20 °C in 29.9 litres, heat the water to about 69 °C (see the strike water temperature). Allow 40 minutes to an hour of heating depending on the power.

Mash in

Put the bag in the pot, fold it over the rim, and pour in the grain while stirring so that no dry clumps remain. Check the temperature and correct it if needed with the mash temperature correction. Cover, insulate, and leave for 60 minutes, stirring once or twice. The mashing guide details temperatures, steps and the iodine test.

Lift and drain the bag

Lift the bag and let it drain over the pot, on a rack or hanging from a pulley. Squeezing the bag increases the volume you recover; brewers' trials show no astringent taste when squeezing at these temperatures.

Option: to gain a few points of efficiency, dunk the drained bag for a few minutes in a bucket of 4 to 6 litres of water at 75 °C, then add this liquid to the pot. This is a dunk sparge; in that case, take the same amount of water out of the starting volume.

Boil

Bring to the boil, then add the hops according to the recipe, usually over 60 minutes. In BIAB, the wort contains a few more grain particles: this does not matter, they will settle to the bottom. Measure the volume before and after the boil the first time to know the real boil-off of your pot (boil-off rate).

Chill and transfer

Put the sanitised chiller into the wort 10 minutes before the end of the boil, then cool to 18-20 °C. Transfer to the fermenter, leaving the hop and protein sediment at the bottom of the pot, measure the original gravity and pitch the yeast.

With the pre-boil gravity and the volumes, the brewing efficiency calculator gives the efficiency of your setup, to carry over into your next recipes.

With an electric preserving pan

A 27 to 29 litre electric preserving pan, with a thermostat and a tap, is a ready-made BIAB vessel and very common among German brewers. Its 1,800 to 2,500 W is enough to heat and hold the mash; the boil is gentler than on gas, with the lid ajar.

The capacity limits the volume: about 15 litres of beer per batch. For 15 litres with 3.75 kg of grain, allow 22.7 litres of water at the start and 18.9 litres before the boil. Check that the appliance is designed for a prolonged boil and fit a false bottom or a rack so the bag does not touch the element.

Small batches: 5 litre kits

5 litre gift kits often contain a mix of crushed grain, a sachet of hops, yeast and a demijohn. They are brewed like a BIAB in the kitchen: a 10 litre saucepan, a bag or a large fine sieve, and the same process on a small scale.

For 5 litres with 1.25 kg of grain, allow about 8.3 litres of water at the start and 7 litres before the boil. The rest is identical: a one-hour mash around 66 °C, boil, cooling in the sink, fermentation in the demijohn with its airlock. A 5 litre batch fills 13 to 14 bottles of 33 cl.

Common BIAB mistakes

• A pot that is too small: with the grain, the level rises by 3 to 4 litres for 5 kg, and the wort boils over.
• A bag that touches an element or the bottom of a gas-heated pot: it melts or burns. A false bottom or a rack solves the problem.
• A temperature that drops during the mash for lack of insulation: the beer comes out sweeter than planned.
• A crush that is too coarse: in BIAB, a fine crush is possible since the bag filters, and it improves efficiency.