Brew in a Bag (BIAB) – A Simple Guide


Brew in a bag (BIAB) is a form of all-grain brewing where you mash and boil in the same vessel, it’s gained popularity with both extract brewers looking to step-up to using grain and also with all-grain brewers looking to simplify their process. In this post we’ll cover pro’s and con’s, the process and some useful tips if you’re thinking of trying it out.





BIAB Pro’s

-       Fantastic quality beers

-       Lower investment cost than standard all grain set-up

-       Shorter set up and brew day (should shave about 1.5-2.5hrs off your brew day in comparison to a full all-grain method)

-       Less Cleaning

-       Using a full grain bill, mash and boil; for more authentic beers than from extract

-       Ideal for ½ batch (12.5L) or smaller  


BIAB Con’s

-       Difficult to do a large batch (23L or higher), as requires a pulley system to lift grain, a large pot and an external heat source

-       Lower efficiency than a full AG system

-       More involved than simple extract kit brewing


Equipment Required


For ease, efficiency and minimal equipment when you’re setting out; we’d recommend a set-up as detailed below to yield approx. 13L of beer / batch. If you want to scale this up/down get in touch and we’ll happily point you the, the core process remains unchanged despite batch size.


If you’re already brewing with one of the Brew UK starter kits, you’ll only need a couple of additional items to switch to a BIAB set-up, these are:


30L Brew Pot – size can vary if you’re doing more or less volume, but for a 13L fermentation that’s what’s required, in general your pot should be >2x fermentation size.


Grain Bag - a fine mesh material bag that’s large enough to line the entire inside of the boil pot (not just sit inside it), and have a drawstring or tie at the top to allow the bag to be closed. We stock one that’s ideal here


A Digital Thermometer to monitor wort temperatures throughout mash and boil, one such as this works perfectly.


Also nice to have:


An Immersion chiller or wort cooling apparatus, to allow you to quickly chill your wort after the boil


A steel mixing paddle which is more durable than the plastic versions, a lot more durable, especially when working with boiling wort. This one works great.


(If you want to brew a full-scale 5-gallon (23L) scale BIAB, as well as a bigger pot you’ll also need an external gas burner like the one we sell here).


Brewing – Recipe and Process


Most of the established recipe creation software available have settings for BIAB, If you need a hand with a recipe creation for this the ones on our site here are a great place to start.

1. Add 21L of water into your brew pot

2. Heat water to approximately 71° C — or to 4-5° C warmer than the mash temperature detailed in the recipe (most call for a mash temp between 64—70° C, depending on the beer)

3. Turn off the heat and line the kettle with the mesh grain bag

4. Add crushed grains slowly, stirring well and breaking up any clumps

5. Ensure temperature is stable (at mash temp specified in recipe), cover and rest for between 60-90mins (again recipe will dictate this) – this is called the saccharification rest

6. Lift the grain bag slightly out of the liquid wort and allow it to drain into the pot, once drained remove the bag and place in a secondary pot or bucket  

7. Turn the heat back on and bring the wort to the boil, boil for 60mins adding hops and other additions at timings as specified in recipe

8. Cool the wort as quickly as possible and transfer to fermenter

9. The next processes of fermenting, syphoning and packaging remain unchanged from any other brew type

Useful Tips

-       Use a little more grain (<5%) in the mash than the recipe calls for to improve efficiency

-       A mash out, raising the temp of the mash to 75° C and holding it there for 10mins after the 60mins, will also improve efficiency

-       Brew with the bag seams on the outside, this makes it much easier to clean

-       Before raising the full bag, pull the top section over the edge of the pot and allow to stand for 5mins to cool (so it’s easier to grip)

-       Use a false bottom or something to raise the bag 1-2” from the bottom of the kettle to stop it from scorching (remember to add this in at the start before you heat the water)

-       Don’t lift the grain bag too high above the wort when draining, or it will splash – you’ll make a mess and get losses, just above the wort level is fine

-       A kitchen strainer over your pot makes a great rest for your grain bag when draining

-       Any excess wort in the second pot/bucket can be put back into the brew pot for the boil

-       Make notes of the losses you experienced, timings, temperatures etc – this will all be specific to your set-up so will help you out when planning your next brew


Hopefully this has whetted your appetite enough to want to try BIAB. If you have any questions or tips for other brewers, please pop them in the comments below. If you need any guidance on equipment purchase before you start brewing please don’t hesitate to contact us.