Hands-on Review of The Brew Bag® for Brew in a Bag (BIAB) Homebrewing



  • The Brew Bag® works great for full-volume, no-sparge mashes.
  • The Brew Bag® can function as a filter inside an ordinary mash tun for regular-volume mashes.
  • Efficiency doesn’t suffer greatly when usingThe Brew Bag®.
  • Clean-up is incredibly easy.

I’d been curious about the The Brew Bag® and Brew in a Bag (BIAB) brewing techniques (pdf) ever since I first heard about them because it seemed like such an easy way to brew. No trouble with a mash tun, no trouble with sparging. What’s not to like?

For those of you unfamiliar, BIAB is a technique where brewers use a finely meshed bag—often just a bag used to strain paint—to mash their grains in a full volume of water. Once conversion of the starches during the mash is complete, they simply lift the bag from the kettle, give it a few squeezes to extract as much wort as possible, and then continue on with the boil.

BIAB does have its difficulties. The grains can get very heavy, so many brewers using this technique install a pulley system in the ceiling of their garage and use ropes to pull the grains out. This sounded expensive and difficult (and I’m renting, so I can’t just drill into my ceiling), but I still wanted to see if a bag might work in the Goldilocks Homebrewing system.

The folks at brewinabag.com, purveyors of The Brew Bag®, make mesh bags that are designed for specific kettles and mash tuns. You’ll get a great fit no matter what kind of container you use—they’ll make one especially for you. The bags cost $30, so it’s about the same cost as buying plumbing to fit your mash tun. I’ve used one on two batches in my 5-gallon Igloo cooler mash tun over the past month.

One Gallon Batch

First I wanted to try a typical, no-sparge BIAB situation, so I put together a simple one-gallon batch of beer—a 100% Pilsner, Amarillo hop SMaSH (Single Malt Single Hop) beer. I was aiming for 1.25 gallons of 1.050 wort, so a total of 62.5GU (1.25 x 50 = 62.5), and I would leave the quarter gallon in the kettle. I assumed that I would get a slightly lower efficiency than normal and calculated everything with 65% in mind.


I mashed in my Igloo cooler in 2.5 gallons of water just to maintain the temperatures better, but I easily could have done this in my kettle.


brewinabag.com provides instructions about how much water you can expect to be absorbed by the grains and recommends mashing at full volume. I had signs of lack of conversion in an iodine test after an hour, so I let it mash longer. Part of this could be that my mash temps dropped into the 146F range by the end—less thermal mass with small batches mean you won’t hold the temperature as well. This probably wouldn’t have been a problem with larger batches and was no fault of The Brew Bag®.


When I was done, I simply lifted the grain from the cooler.


And plopped it down into a big pot.


I ended up with 2 gallons of wort at 1.032, which works out to 64GU total—right on the nose. This suggests that I was slightly more efficient than 65%, which is good: it looks like The Brew Bag® does not affect efficiency. I also managed to squeeze out about two cups of extra wort from the bag itself, which I froze and used to propagate yeast for my next batch.

I just bottled this beer and it’s carbonating at the moment, so I don’t know exactly how it turned out. It seems fine. I used dry yeast for the first time in a while, but after a super slow start I panicked and ended up pitching a small sample of British ale yeast I’d saved from previous batches. So I might have some sort of Franken-beer on my hands. This just goes to show you that equipment isn’t everything, especially mash equipment. Mashing is really just the first step, and yeast treatment is very important. I don’t think I’ll be using dry yeast again in the future.

Four Gallon Batch

As you may be aware, I don’t ever brew 5-gallon batches. I boil on my stovetop, so I’m not sure I could get that much liquid to boil. I’ve been able to get 5-gallons rolling for a 4-gallon batch, so maybe I should man up and try a 5-gallon batch sometime, but in general 3-4 gallons is enough beer for me.

I wanted to test The Brew Bag® as a replacement filtration device during a normal sparge, so I cooked up a recipe for a Belgian Dubbel from Brewing Classic Styles. This time I calculated everything at 70% efficiency. I was aiming for 4 gallons of 1.056 wort, which I planned to bump up to 1.064 using adjuncts during fermentation.


In the end, I decided to add more base malt to get me up to 1.062, so 248GU total. I wanted to make the beer stronger, and I felt like bumping up the base malt would also compensate for any inefficiency from The Brew Bag® (even though my first test showed no effect on efficiency using the bag).



I fly sparged as usual, and this is the data I got as I sparged:

1 gallon: 125F 1.074 = 1.084 = 84GU
2 gallons: 124F 1.070 = 1.080 = 160GU
3 gallons: 122F 1.060 = 1.069 = 207GU
4 gallons: 121F 1.046 = 1.055 = 220GU
(An additional test at 4 gallons with the hydrometer just floating in my bucket of wort: 131F 1.043 = 1.054 x 4 = 216)
(At this point the wort was running out at 144F 1.010 = 1.024)
4.5 gallons: 130F 1.040 = 1.051 x 4.5 = 229.5GU
5 gallons: 130F 1.035 = 1.046 x 5 = 230GU

The numbers started to get a little funny toward the end, and I think my final readings at 4 and 5 gallons may have been off, especially if the wort really was running out at 1.024. After boiling and cooling the wort, I had an original gravity of 1.066 and just over 4 gallons, which means about 264GU total…much more than I was going for, and about 75% efficiency. Additional testing will be necessary to see how efficiency fares.

BUT BACK TO THE REAL STORY, The Brew Bag® worked perfectly. The sparge slowed down toward the end. I was getting about 12 mins/gallon in the beginning which slowed to about 15-16 mins/gallon by the end. I got just about all the GU I needed, well within the style limits for Dubbels. I pitched a nice set of healthy yeast and had a vigorous fermentation. It’s been in the primary for about ten days now, and I plan to let it take all the time it needs.


Clean-up was a total breeze with The Brew Bag®. I drained the rest of what I could into a jar to save as starter wort (I managed to get about 6 cups of 1.035 wort), and then I pulled the bag out of the mash tun and set it in the tub.


When I pulled it out, I heard a soft burping sound, and a bunch of wort rushed out. This makes me think that toward the end I was starting to get a slightly stuck mash. Perhaps I could have tried to jostle The Brew Bag® a bit, recirculate for a quart or so, and then continued to collect wort. At that point, I’d already collected my volume, so it wasn’t a huge deal, but I might’ve been able to save more starter wort.

I ran some cold water through the spent grains to cool them down a little, and then I simply upended The Brew Bag® into a trash bag and threw it all away.


After dumping the grain, I washed down The Brew Bag® using the soft side of a sponge and dish soap before hanging it to dry.

All in all, I highly recommend using The Brew Bag®. Clean-up alone is worth the cost in my opinion. It saved me about 30 minutes of trouble draining and then tossing the spent grain, not to mention clearing all the plumbing of grain particles.

I’m curious to try it out again and gather more data about the efficiency so I can start to dial it in. If you were considering picking up The Brew Bag®, I’d say go ahead and give it a shot.

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