Brew in a bag

BIAB is the easiest and usually cheapest way to make an all-grain beer. It is growing in popularity because it is simpler and quicker than other methods of all-grain brewing and requires only one vessel, meaning it needs less investment and less room.

Many brewers do BIAB in a large stockpot on a stovetop or in a 40-litre electric catering urn. Most BIAB brewers do not rinse, or sparge, the grain once the mash is finished. This means that slightly more grain is required to make a beer of the same gravity, compared with a method in which the grain is sparged. However, grain is fairly inexpensive so the slightly higher cost is not a consideration for most homebrewers. On the upside, some people believe that the grain not being sparged results in a fuller malt flavour.

Choosing a vessel

In BIAB, heating the mash liquor (water), mashing and boiling are all done in the same vessel, unlike 3V and other types of brewing where separate vessels are used to mash the grain, boil the wort, heat the sparge water and, sometimes, heat the mash liquor.

For that reason, the vessel needs to be large enough to hold the combined volume of the mash liquor and the grain. Something about 40 litres works well if you intend to produce about 20 litres to 23 litres of wort to ferment.

Urn v stock pot

Electric catering urns are very popular among BIAB brewers. The built-in electric element means that heat does not need to be applied to the vessel to heat the water, and urns come with a tap fitted, which allows the boiling wort to be safely and easily transferred to the fermenter or cooling vessel.

Large stock pots are the other option for BIAB. They are cheaper than a catering urn. Many BIAB brewers opt for stainless steel pots because stainless steel is harder-wearing than aluminium. However, aluminium conducts heat better and is cheaper but prone to pitting if the quality is not up to scratch or it is cleaned with products that react with aluminium, such as bleach.

Heat source

If you've decided to BIAB using a catering urn, you have a built-in heater. But if you are using a large pot you will need some way to heat the mash liquor and boil the wort. Sometimes it is also necessary to apply heat to the mash if its temperature drops too much during the mash.

You have a few options to heat water in a pot. The first is an immersion element. The most common type is about 2000 watts. You can hold them and move them through the liquid while mashing to raise the temperature evenly, or hang them on the side of the pot during the boil.

The second option is to heat the vessel from underneath, by gas or electricity. Using a ring burner and gas cylinder or natural gas is probably the more common approach, and has the advantage of being portable. If you decide on a gas burner, make sure you only use it in a well-ventilated area. While heating on a kitchen stove is possible, it's not advisable for reasons including there will be a lot of condensation, that brewing can be messy (particularly in the event of spillage) and if you need to lift the vessel then stove height is not ideal and that if you plan to use a wort chiller you'll need to run a hose to a tap with an appropriate fitting, which is usually outside.

The "bag"

Most BIABers use a bag made a synthetic fabric called Swiss voile. Swiss voile is finely woven so that it doesn't let small particles of grain escape, but lets water flow through it relatively easily. Most brewers buy a ready-made bag, which are available cheaply from many homebrew stores, while some make their own with fabric bought from haberdashers or curtain shops. Ideally, the bag you use will have a draw-string so that it can be tied closed. The draw-string is not designed to hang the bag from when it's full of wet grain and you've pulled it out of your mashing vessel.

An alternative to a bag is an insert made of fine stainless steel mesh. Some brewers also use a pot that fits inside the main mashing vessel that has holes drilled in the bottom to allow the mash liquor in and the wort to drain out when the mash is finished. An advantage of the pot system is that it can be supported over the top of the BIAB vessel with a couple of metal rods to drain the grain, similar to how a Braumeister is used.

Step by step: Brew in a bag

All these steps assume you have worked out the recipe, including mash temperature, mash volume, hop additions, etc, manually or with brewing software. Thanks to member Jello for the photos in the tutorial below.

  1. If you are using an urn with an exposed element you will need something to protect the bag so that it doesn't melt. A cake rack or roasting rack in the bottom works well. If you like, attach a piece of string to it so you can pull it out when the mash is finished.
  2. Fill the brewing vessel with the required amount of water. If you've got an instant hot water heater use hot water to save time. However, if you have a storage hot water service, which heats the water ready for use, then test the water first to make sure it doesn't have unpleasant flavours from the storage tank. To do this, put some hot water in a cup, allow it to cool and drink it. If it tastes fine it should be fine to brew with. If not, start with cold water.
  3. Turn on the heat and use your thermometer to monitor the temperature until it reaches "strike temperature", which is the temperature at which the liquor will be when you add the grain. This will be higher than your mashing temperature because the grain is a lower temperature and will cool the mash a few degrees.

    Gas-fired boiler setup ready for BIAB.

    Gas-fired BIAB setup ready to begin mashing.

  4. Put the bag into the brewing vessel and fold the sides over the edges of the pot.
  5. Slowly pour in the cracked malt and grain, stirring constantly to make sure all the grain is wet and that there are no "dough balls". This step is easiest if you have a brewing assistant because trying to pour grain while stirring the mash is not always easy!
  6. Measure the temperature. If your calculations were correct you should be fairly close to your target mash temperature. If necessary apply some heat to raise the temperature. If it's a degree or two too hot don't worry. Add a little cold water and stir until the temperature drops.
  7. At this stage you have two options. The easy option is to put the lid on and wrap the brewing vessel in blankets and quilts to insulate it. This will maintain the temperature while the mash occurs. Halfway through the mash unwrap the brewing vessel and take a temperature reading. Apply heat if necessary to bring it back up to temperature. Many brewers don't bother with this step, and simply start the mash at a slightly higher temperature, knowing that they will lose a couple of degrees over the course of the mash. The other option is to stir constantly and measure the temperature for the duration of the mash, applying heat when necessary. Some brewers believe the constant stirring results in greater mash efficiency (more starch being converted to sugars).

    Near the end of mashing and there is a lot of foaming.

    Near the end of mashing, and there is a thick foam on top of the liquid.

  8. At the end of the mash, perform a "mash-out" by raising the temperature to 76C and holding it for 10 minutes. This step has two effects: to "denature" or kill the enzymes that had been converting starch to sugar, and to make the liquid in the mash more runny so that it drains better.
  9. Gather the opening of the grain bag together.
  10. Pull the bag out of the brewing vessel. Many brewers tie a rope around the top of the grain bag and use a pulley to hoist the bag out. Suspend the bag above the vessel or another container, or just place it in a clean bucket, because a lot of liquid will drain out.
  11. Take an SG reading.

    Grain and bag removed, ready for the boil

    After the bag is removed the sweet liquid is ready to be boiled.

  12. Turn on the heat and bring the liquid to the boil.

    The liquid at a rolling boil, ready for the addition of hops.

    The liquid at a rolling boil, ready for the first addition of hops.

  13. Add hops and any other ingredients at the times recommended in the recipe, and any finings 15 minutes from the end of the boil. Finings help coagulate proteins that would cause hazy beer, and make them fall to the bottom of the boiler.
  14. At the end of the boil, turn off the heat, stir the wort gently to create a whirlpool and put on the lid. Leave it for five minutes. The whirlpool helps separate the solids and concentrate them in the centre of the vessel.

    The boil finished The bag contains the hops, which prevents them going into the fermenter.

    The liquid - now wort - at the end of the boil The bag contains the hops and prevents them going into the fermenter and possibly fouling the bottling or kegging equipment.

  15. Run the wort through a chiller or transfer it to a sanitised plastic "cube", squeeze out as much air as possible and allow it to cool naturally.

    The wort in a plastic cube, cooling naturally.

    The wort transferred to a cube, in which it will cool naturally.

  16. If you ran the wort through a chiller, aerate the wort to replace the oxygen driven off during the boil then pitch the yeast. If you put the wort in a cube, it can stay there until you're ready to transfer it to to a fermenter, aerate it and pitch the yeast. Because it is sealed in a sanitised container it will last indefinitely.


Tweet it!