Brew in a Bag

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A Simple Guide to Brewing In a Bag

Brewing in a Bag is an all-grain brewing method which differs somewhat from the traditional three-vessel method of brewing. It is an extremely simple method of brewing requiring a low level of equipment, knowledge, and space. It is also highly flexible and the methods highlighted here can be highly modified to suit the brewer’s resources.

BIAB is essentially what I will call a "Full Volume" brewing method where the entire water volume needed for a brew is added to the kettle at the start of the brewing process. This alleviates the need for sparging and sparge water calculations. To simplify the process even further, this guide will also use what is called "escalator mash" in the brewing instructions. This is where the grain is added to the full volume of water shortly after heating begins and then the mash (grain plus the water) is raised to the strike temperature as quickly as possible and then held at this temperature for 90 minutes.

In layman’s terms, BIAB can be summarized as follows: You put a nylon bag in a big pot of water, pour in some grain, heat it to a specific temperature and hold it at that temperature for 90 minutes. At the end of the 90 minutes, the bag holding the grain is removed and then the remaining liquid (hot liquor) is boiled for 90 minutes with hops being added at several stages during the boil. After the boil, the resulting wort is cooled rapidly and the yeast pitched. All other stages of the brewing process should be familiar to those who have done some kit brews.

Equipment Needed

Mash Bag Material and Construction

The mash bag should be sewn so as to form a liner for the brewers kettle similar to the way in which a garbage bin liner fits in a bin. Nylon material should be used throughout. The materials can be easily purchased from Spotlite for around $10. These materials are:

  • Fabric: 100% Swiss Voile Ivory
  • Thread: Any White Nylon Thread
  • Drawstring: Gutterman Poly Thread.

Creating a Beer by BIAB

Let’s get underway!

Our brew day time officially starts when water is added to the kettle and ends after the fermenter is sealed and original gravity reading taken. These instructions are based on using a 70L (18.5 gal) Robinox pot as the kettle. Where appropriate, notes will be made in these instructions on how the kettle size and shape affect the procedure.

Should you have a smaller pot, this is not a problem. In fact, you could scrape by with no changes to these instructions with a 40L (10.5 gal) pot. If you have a smaller pot size, either make a smaller batch or just add top water when you can throughout the brew day. To do this, some knowledge of hop utilization and "single-sparge" brewing will be very helpful.

To start the brew day, fill the kettle with 38L (10 gal) of water. Before your first brew, you should calibrate your kettle using a jug and stainless steel ruler. Simply add known quantities of water to the kettle and make a note of how deep the water is in the kettle at each level. My Robinox, unlike a keg, is even in shape and calibration has told me that every litre added to the kettle increases the water depth by 0.61cm. So, to add 38L of water to the kettle, I fill it to a depth of 23.2cm. When measuring the depth, hold the ruler in the centre of the kettle just in case the kettle is not based on level ground. Many brewers use kettles that are keg-like in shape. These are taller and narrower than the Robinox and so evaporation levels are less. I would, at a guess, suggest that these brewers reduce their initial volume of water from 38 to 33L (10 to 8.7gal). While the kettle is filling, add the mash bag to the kettle and turn your burner on as full as possible without flames leaping up the sides. Burners come with air adjustment rings which should be adjusted so that the flame is blue— no yellow. Make sure that your mash bag is in no danger of burning.

When the kettle has been filled to the required volume, add the grain. To do this, simply pour it reasonably quickly and evenly over the surface of the water from a height of about 40 cm (15") if possible. Pouring in this manner avoids the grains clumping together. Once this is done, agitate with the mash paddle to make it spread evenly and to ensure that no grain has clumped (very unlikely.)

After the grain has been poured and agitated, raise the temperature of the mash to 66°C (150.8°F), at which time the mash officially starts. In the case of this equipment, this takes about 20 minutes, although the checklist allows 35 minutes for this. When 66°C (150.8°F) is reached, either turn off the flame or have it on very low (very unlikely). To conserve temperature, put your lid on the kettle but have the mash paddle handle poking out. Once done, have a 5-minute break to check that you are on track and review the mash checklist. Start timing your mash when you have finished this check.


The mash section is very easy. All that is required is several temperature checks and then the weighing out of hops. Most of the mash conversion takes place in the first 20 minutes and so the checklist has 5-minute agitations and temperature checks during this period. With my equipment, I usually only have to turn the 2nd ring of my burner on for about 5 minutes at the 40-minute mark. At this stage, the mash has usually dropped to about 64.5°C (148.1°F). I raise it to 67°C (152.6°F) and then leave it for the remaining 50 minutes. This keeps things simple.

Use electronic scales and 3 washing powder scoops to measure out my boiling, flavour and aroma hops. The scoops are labeled 1, 2 and 3 with permanent marker. If you don’t have scales, just divide your known quantity of hops up as best as you can. Only use hops that are fresh and green and are labeled with their alpha acid rating. Once you have done the above, while waiting for the 90-minute mash to end, take another break, do a check and also review the "Mash Ends" checklist.

The Boil

This section involves removing the mash bag and raising the resultant sweet liquor to the boil. Firstly, light your burner and adjust to full heat. Then place an empty bucket as close to the kettle as possible. Lift your grain bag slightly above the kettle liquor level and twirl the bag around to get rid of excess liquor. Then simply dump the bag into the bucket. (I then suspend the bag from a door handle to help draining.) Ten minutes later give the mash bag another squeeze and then dump the bag somewhere appropriate. I dump mine in the laundry sink. Pour the few litres of sweet liquor that you have gained from draining and squeezing into the kettle.

Whilst not essential, doing a volume and gravity check at this time will give you an "Efficiency into Boiler" figure, which can be interesting. This can be done with your hydrometer or, for those a little less financially challenged, a refractometer. First, use your stainless steel ruler to check the volume in the kettle. Sweet liquor expands when it is hot, so multiplying the figure you have by 0.95 will give you a more accurate volume figure.

Remove some liquor from the kettle to use for a hydrometer reading. Let it cool to 20°C (68°F) before taking the reading or use tables to compensate for the temperature. While waiting for the liquor to start boiling, check that you are on track and review the boil checklist.

A good rolling boil is necessary to produce a good beer. Saving 50 cents on gas or trying to boil more liquid than you are capable of should be avoided. Our recipe allows for a 90-minute boil. If time is very important to you, then you can reduce both the mash time and boil time to 60 minutes to save an hour off the brew day. I suggest new brewers avoid this. Take your time!

You may notice as the brew starts to boil a creamy foam forming. Some people advocate skimming this off with a strainer. I have included this step because, if for no other reason, it will force the new brewer to keep an eye on the brew. Boil-overs are not a problem with a 70L (18.5gal) pot as a kettle. With smaller kettles a boil-over is a problem, so keep your eyes on the kettle.

After skimming, suspend your hop sock in the kettle. A hop sock greatly reduces trub (solids forming on the bottom of your kettle at the end of the boil.) If you cannot afford a hop sock, then you can thoroughly rinse your mash bag and re-fit this to the kettle. I use 2 hanging basket hooks from Bunnings to suspend my hop sock.

The checklist then tells the brewer to add hops and a teaspoon of table salt into the hop sock. The addition of hops may once again cause a boil-over, so keep your eyes open even wider! At this stage, there is an hour’s gap until the next hop addition. Boiling wort has a mind of its own. It may stop boiling or boil over for unknown reasons at any time. Like a 3-year-old, boiling wort seems to know what you are doing at any given time and uses the times when you are not watching to cause mischief. As your brewing skills increase along with your equipment knowledge, you will develop what is best known as a "feel" for boiling wort. Until you develop these eyes in the back of your head, monitor the boil constantly.


Turn your chiller on if you have one. Agitating the wort from time to time speeds up the cooling process. To do this, simply lift the paddle handle up and down a few times. Chilling your wort will greatly depend on your equipment and tap water temperature. The checklist allows for a 25-minute chill, but this could be an hour or even longer.

If you do not have a chiller, you have several options available to you. The most accepted procedure is to cool your wort as quickly as possible using whatever means available- water baths, ice baths etc. Your kettle may even fit in your sink where you could adjust tap flow so that water enters the sink as fast as it leaves. When doing this, you don’t need much water flow. I would estimate from 0.75 to 1.0L per minute is adequate. Depending on your tap water temperature, you may have to add ice towards the end of your chill to reduce the brew temperature to 25°C.

Another chilling method is to allow the brew to cool naturally inside a sealed container. This is a method that many brewers are comfortable with. During the chill it is necessary to monitor temperature. Initially this can be done by agitating the wort and then feeling the side of the kettle. Obviously doing this straight after flame off is unnecessary and will lead to burns. Use your common sense to feel the kettle sides and work out when a proper thermometer check should be taken.

Any brewer using this method should also be well aware of the dangers of infection during the gap between boiling and pitching. For this reason, before taking any temperature checks, ensure that your thermometer is cleaned and sanitized. To make things easier for newer brewers, the BIAB checklist requires the wort to be cooled to around 25°C. Anywhere from 16-30°C will be fine though. When you hit this temperature range, you can stop the chill. If you have poor equipment for cooling your fermenter, aim for the lower end of the above range but do not go under 16°C. When you reach your chosen temperature, stop the chill and review the Pitch checklist.

Pitch The Yeast

After cooling is completed, I use 2 bungs to tilt the kettle. This is done because the Robinox has such a large diameter. Tilting allows the maximum amount of wort to be siphoned off. Once tilted I leave the kettle to settle for ten minutes during which time I sanitize the auto-siphon and empty the equipment and sanitizing solution from my fermenter into my bucket. I then set the fermenter and large jug up below the kettle ready for siphoning.

To assist with clarity, I siphon the first 200mL or so into the empty jug pinching the siphon tube as soon as I see the wort running clear. I then transfer the siphon into the fermenter. If you have aeration equipment then put your sanitized hose and stone into the fermenter and turn your air pump on while the wort siphons.

If you do not have a pump and airstone then just allow the wort to splash when siphoning. In other words, have the end of the siphon tube at the top of the fermenter. Obviously, the cleanliness of your brewing area will affect how much you can aerate in this way without increasing the risk of infection to an unacceptable level.

Monitor the siphon tube, pinch and remove it as soon as you see the clarity deteriorate. If you have a 25L fermenter then you may have to stop the siphon before clarity deteriorates i.e. when the fermenter level reaches the 23L mark. If this occurs then continue to siphon into the spare jug so as you can measure how much extra wort you had. Knowing this will help you adjust your initial volume on your next brew. It will also allow you to determine an efficiency into fermenter figure.

Remove any aeration equipment.

If your wort became cloudy and you had to stop siphoning before the 23L mark, then add some water that has been boiled and cooled into your fermenter now to achieve the 23L level. You can even use tap water for this if your water tastes OK.

Now sprinkle your yeast evenly over the surface of the wort and seal your fermenter.

Take a hydrometer sample immediately so as you can determine your efficiency into fermenter figure as well as your original gravity. When calculating your efficiency figure, add any litres that you couldn't fit into the fermenter.

KkRm7c Major thanks for the article. Awesome.

External Links

For an in depth discussion about BIAB, see this thread

BIABrewer [1] aims to provide the latest information on BIAB.