Sparging BIAB on Brew Day (Essential Guide of What to Do!)


Homebrewing is a hobby, nay a calling, which is full of contradictions and opinions. Ask the same question and you’ll get many different answers, the same can be said of sparging a BIAB brew.

So, should you sparge your BIAB or not? The concept of BIAB is to make brewing easier & to combine the mashing and lautering processes in one pot. So yes, you can skip any additional sparging of your grains and still make a quality beer. But, there is some evidence to suggest that more fermentable sugars can be extracted through sparging.

To be honest, there are many different approaches to this topic and you would get so many contradictory ideas if you researched this online or asked around your local brew club.

So, in this article, I have gathered together all the approaches I have found and reduced them down to the key ideas you need to know. Stick around and find out more about whether or not you really need to sparge a BIAB brew.

What is BIAB?

BIAB stands for Brew In A Bag and is a relatively new brewing technique. It’s designed to make all-grain brewing less complex and perhaps more accessible to the wider public. By placing your grain into a brewing bag you are able to mash them and lauter them all in the same vessel without the need for additional equipment.

So BIAB is a technique which can really save you time and money on your next brew day, but it does raise some questions. The biggest one is whether or not you need to sparge or rinse the grains in the bag after your have mashed them.

This is done in more conventional all-grain brewing to flush out as much fermentable sugar from the grains into the wort reading for the next phase. So, do you need to do this when your grains are practically sitting in a strainer throughout the mashing process?

To Squeeze or not to squeeze

Most BIAB recipes will simply tell you to remove the bag from your mash tun/boil kettle at the end of the mash and either suspend the bag above it or allow it to drip into another container.

However, the grain is always going to absorb some of the water and keep those vital sugars locked away, how do you get at them? Well, the best way most of us can think of is to squeeze that bag like our first prom date.

For many years there has been some controversy over this simple act. Do you squeeze the bag or not? What will happen if you do? Well, many brewers were first very suspicious of the new BIAB technique when it came along. Like most intelligent hobbyist, they were eager to keep the pastime pure and didn’t like any new fangled methods which poured scorn on their tried and tested skills.

Anyway, the rumour got about that you definitely shouldn’t squeeze the bag of grain as you would likely release bitter tannins locked within the grains. Of course, this unwanted addition to your wort could really make your beer taste unpleasant.

But, with most stories of beer folklore the story, if not unfounded, was not entirely accurate. So, after all that blathering, feel free to give your grain bag a good squeeze to release all the liquid which was soaked up during the mash.

A good tip here is to place your grain bag in a colander or similar utensil over the mash tun or container and then place a plate over the top of the bag. You obviously need a big enough colander to fit over the diameter of the pot and also wide enough for the plate you are using. By doing this you get a good even squeeze over the entire bag and you also don’t have to handle grain at 170°F /77°C. Bonus!

Do you need a bigger grain bill for BIAB?

The key concept here is about brewhouse efficiency, which refers to how much potential fermentable sugar you can get out of the grains used with your brewing set up.

As the BIAB process combines the mashing and lautering processes in the same container and doesn’t necessarily call for additional sparging, it could be easily believed that you need extra grain to ensure the right amount of sugars in your wort.

But this isn’t the case. You don’t need to add any additional weight to your grain bill, but you may need to ensure that your grains are adequately crushed and that your brewer’s bag isn’t too fine in its design.

Stuck Mash is a term that basically means that the fermentable sugars couldn’t be extracted from the grain. It’s possible that this could happen if the grain bag isn’t easily permeated by the sugars. This could also be caused by a lower mash temperature which would make the sugars less viscous and easily transferred out of the bag into the waiting wort.

Does BIAB require more water?

Using the BIAB technique doesn’t actually require any more water than used in the more conventional all-grain brewing methods, it just uses it at different times.

The amount of water you use for your mash is less than what you need for your boil. The difference between these two quantities is made up, in the conventional brewing method, through the lautering (and therefore sparging) process. By rinsing the grain bed with additional water we are able to collect enough wort at the right SG level to start our boil.

However, in the BIAB method, the mash water and sparge water are often combined in the mash tun from the start. So, it’s worth considering from the start whether or not you will plan to sparge your grain bag or not. The choice will probably depend on the efficiency of extracting sugars that you experience in your first attempt.

Sparging methods for BIAB

As I said, the jury really is out on whether or not you should be sparging when using the BIAB method. However, here are some methods you can use if you find that your efficiency isn’t hitting the 70-80% level which is expected for most all-grain brews.

Batch Sparge/ Dunk sparge

This is very similar to a conventional batch sparge where additional sparge water is added to a mash tun and allowed to drain through the grain bed. However, with the BIAB twist what you have to do is remove the bag from the mash tun you were originally using and to place the brewer’s bag into a separate pot with additional water (170-190°F) for about 10-15 minutes.

The amount of water depends on how much you need to make up your desired quantity of wort for your boil. So, if you are 2 gallons short, you should batch/dunk sparge your BIAB bag in that amount of hot water. Remember to give the bag a good squeeze before you transfer the wort collected into your main boil kettle.

Faux-Fly sparge

Although not exactly like the normal way you might fly sparge an all-grain setup, here you will be adding water over the grain in the bag rather than submerging it.

You can do this either with a second pot or even directly into the main boil kettle you will be using later. The main thing to remember is that unlike in traditional fly sparging, no wort will be let out of the container so you want to be very careful of the amount you use so that you don’t dilute the SG too much.

The best way to do this is to put your brewer’s bag into a colander and pour small amounts of your additional sparge water onto the grain. If you flatten the bag out beforehand you can be sure that the flow of water through it will be more evenly spread and you’ll up your efficiency by doing this.

Again, remember that you are aiming to collect enough wort for your boil, so only use enough additional sparge water to compensate for the loss of liquid through evaporation and absorption in the mashing phase.

For more information on sparging with conventional all-grain recipes, check out my in-depth article on all you need to know about sparging.

What should you do if your specific gravity is off?

A lot of brewers who attempt the BIAB technique for the first time find that their efficiency is off and that the lack of fermentable sugars in their wort has thrown off the expected specific gravity.

If this has happened to you, rinsing the grain continually will only dilute your wort more and make the issue even worse. So, do you have to start again? No, there is a quick solution.

The best piece of advice I have found is to keep some dry malt extract (DME) handy for just such occasions. You can simply add enough DME to your collect wort to bring your SG up to the levels you were expecting.

Of course, this is only a temporary fix to an annoying brew day problem. Make sure that you always keep accurate notes of all your actions and measurements, that way you can analyze them later (with the help of the community too) and find out how you can avoid having to use DME again in the future.

Is a mashout necessary for BIAB?

A mashout is when you raise the temperature of the wort in your mash to around 170°F (77°C) at the end of your mashing process. This is generally aimed at mashes with a ration of 1.5- 2 quarts per pound of grain (1.4-18 liters per 453 grams). A mashout is also designed to help sparge water pass through the grain bed with extracted sugars by making those sugars more soluble. At the same time, it puts an end to the activities of the enzymes which have been converting starches into sugar during the mash.

So, if you are planning to simply remove your brewer’s bag and give it a squeeze, a mashout doesn’t really give you anything extra. However, if you are planning to do any sort of sparging, then you may want to take the extra 10 minutes to complete the mashout.

Phil - BeerCreation

Hey, I'm Phil. I'm passionate about all things beer. I love making it, drinking it and best all, learning about it!

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