BIAB (Brew in a Bag) - How To!

Brew in a Bag (commonly referred to as BIAB) is a method of brewing that eliminates the need for a mash tun and consolidates brewing into a single vessel prior to fermentation.

To understand how BIAB differs from other methods of brewing you must first become familiar with the language that brewers use (which is needlessly complex so apologies in advance) but more importantly how you make beer. If you know how beer is made then you can skip the next few paragraphs and jump directly to the ‘How does BIAB work?’ section.

What's beer made of?

In simple terms (and let me stress the simple aspect!) beeraa
is made by introducing sugar to water then adding yeast and leaving it somewhere cool. The yeast ‘eats’ the sugar and converts it into alcohol. This, in a nutshell, is how you make simple alcoholic beverages.

The sugars in beer come from a variety of sources but the foundation of any great beer is malted grains. Malted grains are simply grains taken from various crops (wheat, barley, rye etc.) that are then specifically cooked. The grains take on various properties due to the heat (the science is interesting but not necessary to know) that activate enzymes which break down complex carbs into simple sugars . Now that you have your sugar and water combined you introduce yeast and voila – you have beer.

Alright, so how does BIAB work? What do I need?

Brew in a bag is a method of brewing all-grain. All-grain is a fancy way of saying that you are going to brew from scratch by first breaking the sugars away from your malted grains in hot water to get sugar-water. The sugar-water is known as ‘wort’ and that’s what we’ll refer to it as from here on out.

To start a BIAB brew day you’ll need a few bits of equipment which I’ll list below:

  • A big soup pot (commonly referred to as a ‘brew kettle’ this should be –at minimum- 5 Gallons in capacity)
  •  A straining bag that is big enough to fit in your pot.
  •  At least one FV (FV stands for ‘fermentation vessel’ which is generally a big plastic bucket)
  • A thermometer (either electronic or manual – having a couple handy will give you a better reading)
  •  A hydrometer (a hydrometer is used to measure the ‘gravity’ of your wort and, later, your beer.)
  • A big spoon (like a real big soup spoon, maybe a foot long or so)

Pro Tip: All of these items can be found in Homebrew Kits which are put together in order to help new brewers not have to decide what they need to get started!

Shop Starter Kits

There are a few stages to brewing but BIAB cuts out a few steps to make brewing quicker, simpler, and easier. The aim of your BIAB brew day is to:

  1. Separate the sugars from the grains to get your wort.
  2. Boil the wort for the desired amount of time and add hops.
  3. Cool the wort down so you can add the yeast without killing it.

Getting the Brew Day started!

Step 1 - The Mash

Look, I get it – I was impatient and eager to get started on my first brew – perhaps you’ve skipped straight to this section thinking you know everything you need to know about the theory. Maybe you’ve read the whole thing. Either way, you will make mistakes but you will learn from them! It really is very very difficult to completely ruin beer.

So, with that in mind, let’s get started…

Once you’ve chosen your recipe and decided on the measurements you’ll need to heat up som
e water in your big ol’ soup pot. This is commonly called the ‘strike’ water. There are plenty of calculators online that will help you decide what temperature to heat your strike water up but the general principle is that it must be hotter than your mash temperature. This is because the addition of grains to that water will lower the temperature. A good rule of thumb is to have your strike water be 10F higher than your desired mash temperature. Mashing with the BIAB method

I hear what you’re thinking “Everybody talks about the mash… what the hell is the mash?”. In simple terms the mash is what you get when you combine your water and grains. Like adding milk to cornflakes it becomes a mushy mashed mess of gloopy horrible wetness. And then the magic happens as the sugars separate from the grains and give you your lovely sweet wort.

Put the straining bag into the kettle with the strike water (remember to tie it to the handles so it doesn’t slip, oh and try not to burn your hands!) and slowly add your grains into the bag. Stir them as you add them so they don’t clump up in balls.

Congratulations, you’re almost done with step 1!

Check your temperature in the kettle and make sure you’re at the mash temperature your calculator has suggested. Too hot? Add a little cold water. Too cold? Heat up the kettle from underneath. Now, you’ve got to insulate the kettle as best as possible and allow the grains to mash (that is to steep at a specific temperature) and release their sugary goodness. I use blankets, towels, whatever comes to hand. Let the grains mash for however long your recipe says.

Step 1 complete! (told you you were almost done)Shop All Grain kits

Step 2 – The Boil

With mashing done try and take a pre-boil gravity reading with your hydrometer. Hydrometers measure the gravity of the liquid which is to say how viscous (thick) it is compared to water. It sounds sciencey, and I suppose it is, but for beer purposes you don’t need to know the specifics behind it only the implications for your beer. Every recipe you look at will tell you the OG (original gravity) of the beer and the FG (final gravity). In a nutshell your wort should be made up of water and sugar. Sugar is denser than water so this will cause the liquid to become more viscous (thicker) – not syrup thick (if you’ve got syrup at this point something has gone wrong!) but thick enough that the hydrometer registers a value greater than water. The gravity of water is 1.000. Anything greater (1.050, 1.110 etc.) indicates there is something altering the composition of the substance (in this case, sugars) to make it thicker.

boilTaking a pre-boil gravity will give you an idea of how efficient your mash technique is. Efficiency is something that homebrewers and commercial brewers alike strive to increase and it simply means “How good was your mashing technique and did you get all the sugars from the grains?”. The higher the value (which can be calculated using an online calculator) the better. Your first time you might not hit optimum efficiency. The second time you might not either. With every different style of beer you make you might not hit it. But remember, it’s really hard to mess up a beer and if your gravity doesn’t exactly match the recipe you’ve not failed – you might just have a less malty tasting or less alcoholic beer than you had expected. As the godfather of homebrewing Mr. Charlie Papazian says “Don’t worry, relax. Have a homebrew.”

Once you’ve checked the pre-boil gravity it’s on to the boil. At this point you should only have wort in the kettle, no bag and no grains. Start heating the kettle up until you hit boiling temperature and then start your countdown keeping the kettle from boiling over but still having a consistent, rolling boil. Every recipe will differ in regards to hop additions, but remember, a "60 minute hop" is added at the very beginning. Its called a 60 minute addition because it boils for 60 minutes, not because its added at 60 minutes. So, using this logic, a 15 minute hop addition would be added 15 minutes prior to the end of the boil.

Congratulations, step 2 is complete!

Step 3 - Cooling the kettle, pitching the yeast

Once your boil timer is up it’s important to cool the wort bathdown as swiftly as possible. Techniques include placing the kettle in an ice bath (remember to not scratch the bath and also… well… remember to get ice!), leaving the lid on and putting it out in the snow (if it’s that time of year) or using a wort chiller. It doesn’t matter which way you do it, you’ve simply got to get the wort down to a cooler temperature.

Your yeast packet will likely tell you the optimum temperature for fermentation. Use this as a guide for the temperature you have to get the wort down to before pitching the yeast.

Once it’s cooled it’s pitching time. Transfer, orferm
"rack" as brewers say, the wort from the kettle into an empty FV and be sure to aerate it (that is, make sure it catches at least some air and bubbles!), and then drop in the yeast. Put the lid on top of your bucket (or bung if you're using a carboy), fill your airlock up to the fill mark with sanitizer, and fit the sanitizer into the hole of your lid or bung. Now place your FV in a cool place, preferably around 68F with most ales.



Congratulations, you’ve just completed your first BIAB brewday!

About the Author

David Evans is a 30 year old cyclist who balances beer drinking and endurance riding by working out how many miles it'll take to work off a couple of Imperial IPAs... a keen homebrewer for just over a year with his best mate Paul, their attempts at IIPAs have been mostly successful, if overly ambitious!

written by David Evans

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8 comments on “BIAB (Brew in a Bag) - How To!”

  • Mash Tun insulation can be aided by using Winter Jackets (it is winter after all).
    And you can always use 5 gallon paint straining bags from your local Home Depot/Lowes/Menards. They usually come in a 3 pack for under $5.

  • Just curious - do you somehow squeeze as much liquid from the bag of grain as possible? And how do you do it without a trip to the Burn Unit?

    • David Doucette

      There are a couple ways to drain the sugars out.

      First, you can set up a hoist system that holds the bag suspended over your kettle. Just let it drain as you bring the wort to a boil. Squeezing speeds up the process (use heavy duty rubber gloves), but you don't actually need to squeeze.

      Second, You can do a dunk sparge by dunking the grain bag in some hot water and letting it sit for 10-15 minutes. This dilutes the sugars, meaning the liquid the grain absorbs, will contain less sugar than before. It's good for a 1-2% point increase in efficiency in BIAB (about the same as letting it hang suspended).

      Lastly, Do nothing, just mash with an extra pound or two of base malt and just take the bag out and let it drain until you don't want to hold it anymore.

      • I usually just put the bag in a colander in a clean bucket then do a tiny fly sparge (I pour about a quart of 170 degree water through it and let it strain). Then I add that wort to the brew kettle once it reaches a boil. This method can increase your efficiency greatly depending on how high of an OG you are shooting for. Generally the higher OG beers can struggle using BIAB.

  • I currently do BIAB and love it. Convienent, less stuff to clean afterwards, one pot to focus on. As mentioned, 5 gal paint strainer bags from Home Depot/Lowe's works for 8 gal pots or smaller. Adding heat is dangerous and will scorch the bag if not careful causing the grains to spill into the wort when the bag is lifted. Or, you may have a melted bag and burnt grains at the bottom. It sucks and it's messy. I just add more hot water if temps drop. I personally don't squeeze the bag at the end of mashing but lift the bag onto a strainer or oven rack and fly sparge after the bag finish it's dropping. Unfortunately I won't be doing BIAB much longer as I've upgraded to 15gal kettle with a mash tun.

  • Nice write-up. Maybe just one note, and maybe it's common knowledge, but you should let your pre-boil hydrometer sample cool off before taking a reading. I believe most hydrometers are calibrated to 68F and there are calculators to adjust for variations in temperature. But you are going to get a more accurate adjusted reading closer to 68F than you would near your mash temp.

  • What's the best size put to use for BIAB brewing, and how much water is typically used for a 5 gallon batch?

    • David Doucette

      A normal batch (1.05-1.06og) will have the grain absorb about a gallon of water. So ideally you need 7 gallons of strike water, with the ability to boil six without boil-over. So you really want at least 10 gallons roughly. You can get by with an 8 gallon kettle, but you will need a thicker mash, and a partial boil (5 gallons boiled down to 4, so a gallon of top up water roughly).

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