Brew In A Bag : A Simple and Complete Illustrated Guide

Brew in a bag is the perfect way to start all grain brewing – the techniques are simple and the results are great.

This detailed guide explains how to do it.

Brew in a Bag

Brew in a Bag History

Brew in a bag (BIAB) originated in Australia and was initially considered controversial. Many brewers believed it produced inferior beer to all grain methods. However, nowadays it’s use is fairly widespread.

The innovation of BIAB was to combine the benefits of all grain brewing, such as greater choice of ingredients and more control over flavour, with the minimalism of extract brewing, where everything takes place in a single brew pot.

Its simplicity is ideal for beginner brewers who can’t wait to start all grain brewing.

Traditional all grain brewing involves many steps such as steeping malt in a mash tun (often a modified ice chest) before rinsing multiple times in a process known as sparging.

Calculations are performed to ensure that the temperatures and quantities of water and malt are in harmony. The wort (water with malt sugars) that is extracted at the end is boiled and fermented.

That this complicated procedure was developed before one so simple (and effective) is bizarre. Nevertheless, that is the accepted history of the subject.

Equipment For Brew In A Bag

If you already brew with beer kits or malt extract, you should have most of the brewing equipment needed for BIAB.

In addition to the basic kit you’ll also need:

  • a bag

Yes. The only other item you’ll absolutely need to get is a bag made of any light weave, strong fabric. Mine is from a material similar to linen:

brew in a bag bag

The most economical bag is the one you make yourself. In fact, as BIAB is still finding its feet you may struggle to buy a made for brewers bag.

If you opt to make your own, when selecting a fabric choose a strong one. By this I mean that it is able to hold 10-15 kg without breaking. The fabric will act as a filter, holding grains while liquid drains quickly through it. A popular material for many brewers is voile.

An oft-cited limitation of brew in a bag is the inability to brew strong beers due to the difficulty of lifting large amounts of grain from the brew pot. A strong handle will go some way to alleviating this problem.

(Some brewers rig pulley gear to lift the bag from the pot but this is beyond the ambitions of my minimalist setup.)

A good discussion of brew in a bag in general can be found in this article, for anyone interested in finding out more.

Depending on your equipment setup you might consider getting a false bottom for your boil pot.

During the BIAB mash stage, you leave malt (inside the bag) standing in the brew pot, which is filled with hot water.

Malt near the bottom, that is close to the hot stove, will burn unless steps are taken. Many manufacturers supply made to measure disks that fit snugly.

However, a stainless steel colander works equally well:

brew in a bag : false bottom

The perforated false bottom lifts the grains from the bed of the brew pot but allows water to circulate freely through it.

Brew In A Bag In A Nutshell

A quick guide to brew in a bag:

Malt is put into a bag and soaked in water of a pre-determined temperature.

After an hour or so the bag is removed and drained, leaving behind a sugary liquid known as wort.

This is boiled with hops that are added to contribute bitterness, aroma and taste. After cooling, the wort is aerated and yeast are added before the wort is fermented for around two weeks.

The resulting beer is bottled or kegged.

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A Typical Brew Day

The following photos and instructions describe use this English bitter recipe as an example. The steps are the same for any recipe.

1. Prepare The Brew Pot

brew in a bag : heating the water

Fill the brew pot with the water. Unlike with all grain brewing, you will mash with the full boil volume of water.

Unfortunately there aren’t any hard and fast rules about how much water to add, but as a general rule of thumb you’ll need 30 – 50% more than your target volume.

Water is lost to the grains, to evaporation, and to the hop residue that’s left in the pot. A well-draining bag will reduce loses, as will brewing lighter beers (with less grains), and using an efficient stove.

After a couple of brews you’ll have an idea of your own setup’s performance and can adjust the water quantities accordingly. For the English bitter recipe I use 21 litres of water to yield 14-16 litres of beer.

Heat your water to 1°C more than the target mash temperature of the recipe, to allow for cooling caused by the grain addition. When it’s ready, line the pot with your brew bag.

brew in a bag : bag

2. Add The Malt

Weigh the malt according to the requirements of the recipe.

brew in a bag : weighing grain

Take care not to introduce excess air when adding it to the brew pot, or oxidation will occur and cause off-flavours.

Let the grains gently sink into the water. If you’re using finely ground additions (such as the polenta in the example bitter recipe) put that in last so the larger grain hulls can act as a filter at the bottom of the bag.

Brew in a Bag : Grains in Brew Pot

Stir the mash, again very gently, until the grains are submerged and wet.

brew in a bag : wetting grain

3. Mash

The other purpose of stirring is to ensure uniformity of water temperature. You’ll find that the mixture is much hotter towards the bottom, and that it’s difficult to truly measure its temperature.

If it’s cooled significantly during the previous stage (quite likely) add more heat to bring the wort back to temperature. Put the lid on and leave according to the mash schedule, 70 minutes in the example recipe.

brew in a bag : checking temperature

When the time has elapsed lift the bag from the wort and drain, holding it close to the beer’s surface and taking care not to splash and introduce air.

When the wort starts to drip rather than pour from the bag I usually drop it into the fermentation bucket (fitted with another colander style false bottom) so it can self-drain for twenty minutes or so.

You’ll usually get another litre or two of wort by doing this, which you can pour back into the brew pot.

brew in a bag : secondary draining

You’ve made the wort. If you’re familiar with extract or beer kit brewing, you’re at the point you would be after adding the tin of malt. The following steps should be familiar.

brew in a bag : wort

4. Boil

Bring the wort fully to the boil before beginning the hop additions. Once it’s vigorously bubbling you’ll see a yellowy foam form on the surface. These are proteins joining together and leaving the liquid in a process called the hot break.

brew in a bag : boil

Follow the schedule of your recipe to add the bittering and flavouring hops.

5. Cool the Wort, Quickly

A key factor in getting a clear beer is how quickly you cool it after boiling. This stage is the cold break, where more proteins are forced from the wort. I use a bathtub filled with ice bottles for a cooling, but if you have one use a wort chiller.

brew in a bag : cooling

While the cooling down takes place, prepare the yeast. The example recipe uses dried yeast and this needs to be rehydrated in around 200ml sterilised water.

brew in a bag : hydrating the yeast

6. Pitch the Yeast

Once the beer is cool transfer it to the fermenting bucket.

It should be close to fermentation temperature, which for most people is room temperature.

Pour it several times between the bucket and the brew pot to aerate it. This will make it easier for the yeast to multiply and ferment the beer.

This is the only time when air should be in contact with the wort.

Of course, sanitise the fermenter before adding the beer.

Unless you used a hop bag, it’s a good idea to pass the wort through a sieve the first time it’s poured into the bucket. Otherwise, the hop and hot break debris will remain in the beer.

Although it shouldn’t affect the taste too much (unless you leave it fermenting for several weeks), it could cause problems during bottling if the gunk is sucked through the siphon and clogs it.

brew in a bag : aerated wort in fermenter

Put the lid on the fermenter and leave for around two weeks before priming and bottling.

brew in a bag fermenting bucket

Final Thoughts

Here are a few more things to consider as you’re trying brew in a bag for yourself:

  • The temperature is hard to control. Be careful not to overheat the water because it will cool very slowly, and unwanted tannins will be extracted from the malt if it’s too hot. You can always add more heat if you undershoot.
  • Drops of wort dribble everywhere when you remove the bag from the pot. Put something down to protect your stove if you’re worried about that.
  • Because of the relatively unrefined filtering technique brew in a bag beer can be a bit cloudy, especially if you wring every last drop of wort out of the grains. To counter this add whirlfloc or Irish moss for the last ten minutes of the boil.
  • The bag can get extremely hot and heavy when full of water so take care with your hands. It should be big enough to sit comfortably in the water while leaving enough dry fabric for you to grip.

If you have any questions, leave a comment.

Otherwise, try this simple brewing technique and enjoy!

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Comments...

  1. dale dudley

    hi,

    your instructions look great I’m doing kits at moment which I’m enjoying….I’m thinking of beginning my own all grain brewing looking into various ways of building mash tuns etc…Came across this boil in the back method…looks like a great stepping stone to get the idea behind it before making that next step..I already have the equipment from kit brewing…..
    so I’m going to give this a try and see how i get on….

    just a few questions before I get started…..firstly i have book about brewing the beer you love ie recipes for shop bought brew like john smiths, Boddingtons etc….all the recipes are for 5 gallon only how would i convert them to 1-2 gallons i would guess that i would divide the recipe by 5 then x that by how many gallons i want to make? but i guess that’s too easy…..am i guessing correctly or is there a formula to work out the amounts when reducing I’ve already read from your website that you add an extra 30-50%more than target volume is there anything else to think about? i want to make the recipes from this book but in smaller volumes using the boil in the bag method is that possible?

    I look forward to your answer

    Dale :)

    • John

      Hi Dale,

      Here are some answers to your questions:

      Converting recipes
      Resizing is not quite as simple as a straight division and multiplication, but almost. It’s slightly different for hops and malt.

      Recipes usually give malt quantities based on a particular efficiency, which varies from brewer to brewer. Efficiency is the amount of sugar you get out of malt in the mash (soaking in water) versus the full amount of sugar available.

      For your first brew you don’t know your efficiency, so might as well follow the recipe exactly. This does mean simply dividing the malt quantity by 5 and multiplying by your target volume.

      To find out your efficiency for future brews take a gravity reading of the wort before you pitch the yeast. Then enter the recipe and gravity reading into Hopville (or another brewing programme) to compare your gravity with the expected one, and find out your efficiency.

      After 4 or 5 brews an average will emerge and you can adjust your recipes to suit.

      To convert the hops you need to take into account the alpha acid units rather than the weight. This page has more information on those calculations.

      Target Volume
      When you say add 30-50% I think you’re talking about the starting volume of water, right?

      You need to allow for evaporation, absorption by the grain and losses to trub (hop and yeast debris that settles to the bottom during fermentation).

      Again, this is something that varies from brewer to brewer and brew to brew. If your stove is super efficient, for example, and brings wort to the boil quickly you lose less to evaporation. Making a stronger beer (with more malt) you lose more to grain, and so on.

      To give you a rough idea, for an average brew I make about 14 litres (3.7 gallons) of beer starting with 21 litres (5.5 gallons) of water.

      If you want to get into a lot of detail with this I’ve had good results with Brewtarget, but it’s not really necessary unless you’re especially concerned.

      Is it possible to brew recipes from your book using brew in a bag?
      Yes! Because of the efficiency and water loss variables, the first couple of batches may come out weaker, stronger or more or less bitter than expected, but after that you should be able to match a given recipe pretty consistently.

      Good luck and thanks for stopping by!

  2. Ted

    Before you boil, is it really that important to not stir? The oxidation should be pretty minimal and you do oxygenate the wort for the yeast to propagate right?

    • John

      Hi Ted, thanks for the question.

      There’s nothing wrong with stirring the malt during the mash, in fact I find it improves efficiency by getting rid of dry pockets.

      The important thing is to use gentle and fluid movements and avoid introducing air to the wort. Even if the oxidation risk is small, I prefer not to leave it to chance because any air that gets in can bond with elements of the wort and cause cardboardy off-flavours.

      It’s during the mash that this is really an issue. Just before the boil the risk of oxidation is not the same, although I don’t find I need to stir then anyway.

      The aeration before adding the yeast is slightly different. Because the wort’s cool (below 27°C/80°F), the oxygen doesn’t bond in the same way – it’s taken in temporarily. As you say, it’s there to promote good yeast growth.

      That’s how I understand it – hope it helps.

  3. Alexandre

    I’m a begginer and found this way very interesting, mainly to the reduced tuns and equipments needed. Could you tell us which efficiency have you reached with this method? Congratulations for this tips!

    • John

      Hi Alexandre,

      Thanks for visiting.

      I average about 70% efficiency although I’ve had as much as 80-85%.

      When I first started with BIAB I had trouble with efficiency and wrote about it here.

      The main things I’ve found that increase it are:

      • Mixing well at the start to make sure there aren’t any dry patches of grain
      • Mashing for ninety minutes
      • Draining the bag into the fermentor while I heat the wort, moving the grains around every now and again to get out all the liquid. I add this to the rest before the boil.

      Cheers!

  4. Arnie

    I’m about to try my first BIAB. I became confused about hopping when I saw some contraptions on line that consisted of a 5 inch ABS or PVC coupling with a 5 gallon paint straining bag attached. Unless I misunderstood, it appears that the hops are all thrown into the bag at the specific intervals and remained in the wort for the entire boil time. I always have put the specifc hops in separate bags, boiled for the recommended duration and then removed the hop bag before introducing the next variety. Am I missing something here? Please advise. Appreciate you help.

    • John

      Hi Arnie,

      Thanks for stopping by.

      Do you have a link to one of the contraptions? I don’t think I’ve come across those before.

      Usually when hops are added they’re left in the wort for the rest of the boil. It depends on the recipe, but it would be unusual for the hops to be removed before adding the next variety.

      Nearly all recipes state hop additions in time from the end of the boil. For example:

      25g Fuggles for 60 mins
      25g Kent Goldings for 20 mins
      25g Kent Goldings for 5 mins

      With this recipe you throw in the Fuggles 60 minutes before you want to finish. This is usually at the start of the boil. The Kent Goldings go in 40 minutes later, 20 minutes before the end of the boil. 15 minutes later, 5 minutes before the end, you add the final Kent Goldings.

      By the time you finish all of the hops are in the wort together.

      I don’t personally use hop bags because I separate the hop debris at the end with a sieve. If you can easily open your bag during the boil, there’s no need to separate the hop varieties.

      I hope that answers your question – please let me know if not.

      Cheers!

  5. Roy

    I have just done my first brew in a bag and was amazed how much easier than using a tun etc. it was. Conversion was complete after a 90 min mash (iodine test) and I found it just as efficient as using a tun so I don’t think I will use a tun again. If you can hang the bag over the boiler on a rope fixed to a hook above and let it drip for a while after mashing is over its a big help. As a rule of thumb I find 1kg of mashed pale malt will give you 1% abv in a 5 gallon (22.5l) brew. I know some people do better but I never have.

    • John

      Roy, Thanks for sharing your experience and the handy rule of thumb.

      I’ve found the drainage stage to be very useful for getting efficiency up. The wort that drips out is high gravity, at least on my system, and makes a big difference overall.

      I usually leave the bag in the fermenter while bringing the wort to the boil, and then pour the extra in at the last minute.

      Cheers!

  6. Brett

    Great article. Brew in a bag beers have taken off so many prizes in competitions now that there doesn’t seem to be an argument that the beer is in any way inferior.

    Another Aussie discovery is No Chill. The fact is, you DON’T have to chill quickly to create cold break. So for a 24 litre (6 gallon) batch I use a 20 litre food grade water container (they have a little headroom), sanitise it, then drain the hot wort directly into the container, squeeze out any air if possible, and seal. It’s recommended to tip it on its side for a few minutes because the hot wort is an additional opportunity to sterilise the lid. It will cool down to the correct temp in about 24 hours, but you can keep it in the container for much longer safely.
    * No infections
    * Excellent separation of cold break.
    * Pitch yeast when you’re ready
    * Quicker brew day
    * No-chill container (water container) costs about $12!

    • John

      Brett, thanks for the suggestion.

      I’ve heard about No Chill but have never tried it. You’ve made a convincing argument, so I’ll be sure to give it a go at some point soon.

      A commenter on another post is experimenting with no boil brewing at the moment. I’m not sure how that’s turned out yet, but all these things together could make for a very efficient brew day. Great for brewing in the evening when time’s tight.

      Cheers!

  7. dan

    I can confirm that the no chill method is most definitely the way forward I have been doing biab with no chill for about 4 years and touch wood have never had an infection, and as our water is metered I could not justify literately throwing money down the drain. there is truth in the saying old habits die hard, but in my opinion biab and no chill go hand in hand.

    • John

      Thanks for sharing that, Dan.

      The more I hear about no chill the more tempted I am to try it.

      Cheers!

  8. David

    Is it important to have a Second filtration process?

    • John

      David,

      Draining the wort from the brew bag, after you remove it from the pot, is fairly important. Usually a high proportion of the fermentable sugars are in there.

      Is that what you meant?

      • David

        Yeah. That’s what I was asking. Should I pour water over the grain bag while it is draining to help get out any final sugars?

        • John

          You may get a few more gravity points out of it by doing that, but I personally don’t think it’s worth it.

          After experimenting with various rinsing options, I’ve come to the conclusion that draining while lightly turning the grains over inside the bag best balances results with effort.

          The difference between doing or not doing it is big, and the draining fits naturally into brew day. You can leave it dripping into the fermenting bucket while bringing the rest of the wort to boil.

          On the other hand, to rinse you’d need another pot to heat more water, and the few extra points won’t make a great deal of difference to your gravity.

          That’s what I’ve found anyway. It’s definitely something worth experimenting with as you brew more.

          Hope that helps.

        • Roy

          I find it a good idea to pour a 3 or 4 pints of warm water over the bag while it is draining and have had no problems with doing this.

          • John

            I haven’t found the extra rinse to make a big difference, but it’s interesting to hear it’s not the same for everyone. It goes to show it’s worth experimenting, and fine tuning your brewing.

            Thanks for joining in.

        • Roy

          I am using a home made plastic boiler using a couple of kettle elements and did have problems with keeping the temperature right. I have now made a controller using a Simmerstat to control one of the elements will I do my 90 mins. mash. You can get these on eBay for about £10 and its not too much of a job to mount one in a box of some sort. Make sure you get the wiring diagram to go with the one you get as they are not all the same. This fixed my temperature control and it now stays with a few degrees of ideal for as long as I want.

          • John

            Roy,

            Thank you very much for sharing your experience. It’s great to hear about other ways of doing things, and that sounds a useful way of controlling temperature. It can be tricky on a regular stove.

            Cheers.

  9. peter

    Hi John just about to try my first brew in a bag attempt ,what advise for recipe for a beginner with his first brew

    • John

      Hi Peter,

      In a way it depends what you’d like to drink. You can brew most types of beer fairly easily with the basic technique.

      Having said that, if I were you I’d keep it simple while you’re getting the hang of brew day. These recipes are pretty straightforward:

      Light and hoppy
      Bitter
      Dark brown and malty
      Bitter (leave out the corn and make it even simpler)

      Hope that helps, let me know if not.

      Good luck.

      John

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