BIAB: Brew in a Bag – Easy All Grain Homebrew! – Gear, Resources & Reviews

Brew in a Bag, also known as BIAB is a bit of a misnomer.  Brewing in synonym for boiling.  We’re not really boiling in a bag.  BIAB deals with the mashing, lautering and sparging phase of all grain brewing.  What’s really going on is Mash in a Bag or MIAB.  Having said that, BIAB is the term that’s commonly used and we’ll stick with that.

What is BIAB and how is it different from traditional mashing?

In traditional all grain homebrewing a mash takes place in a mash vessel aptly called a mash tun.  During the mash enzymes convert complex carbohydrates into simple sugars that can be fermented by brewer’s yeast.  Homebrew mash tuns take many forms but a typical setup is a cooler combined with a false bottom or screen.  See my post – Hands On Review: Brew Hardware’s Cooler Mash Tun Conversion Kit – Making a Mash Tun – for an example.  After the mash is complete a sparge takes place to rinse residual sugars from the now spent grains.  This can take a couple of different forms in homebrewing either fly/continuous sparging or batch sparging.

in BIAB we simply substitute a bag filter for the false bottom and any required fittings and ball valves.  The cooler is typically replaced by your boil kettle.  Same chemistry behind the scenes and the same basic outcome – complex carbohydrates converted to simple sugars ready to be fermenter.  Just a change in equipment.

Benefits of BIAB

  • Cost savings.  A $10 to $30 bag replaces ~$100++ worth of coolers, fittings, ball valves and false bottom.  Whatever you would spend on a mash tun and HLT.
  • Space savings.  Guess what, that 10+ Gallon Mash Tun takes up space.  It needs to be stored someplace.  A bag folds up to almost nothing, that’s just not true of a cooler.
  • Time savings.  No mash tun to clean up on brew day.  Brew day, for most BIAB brewers, consists of using a single vessel for mashing and boiling.  Also, if you employ a no sparge technique, you cut out another good chunk of time.
  • Direct fired mash tun.  If you use your boil kettle as a mash tun that also means you can direct fire it to maintain mash temperatures, perform step mashes and mash out.  Make sure and stir when applying heat to prevent scorching the bag – or check out the stainless false bottoms linked below.
  • Hit your pre-boil volumes every time.  BIAB really takes grain absorption estimates out of the mix.  If I start with a reasonable water volume (see spreadsheets below for estimating), I can hit my pre-boil volume every time.  I let me bag drip until I hit my pre-boil volume right on the nose and then remove it.
  • BIAB + Small Grain Brewing means entry into homebrewing, starting at the all grain level is easy and economical.  See: Step by Step Small Batch, All Grain Stove Top Brewing

Downsides of BIAB

  • Ingredient costs.  You may use a little more grain to make up for efficiency losses.  Since BIAB is typically (but not always) a no sparge method, some sugars can be left behind.  This is mitigated by a couple of factors.  First, you can crush your grain more aggressively vs traditional mash methods.  A stuck sparge is of little or no concern using BIAB.  An aggressive crush helps to make up for efficiency losses.  Second, I believe that a full volume mash (as is typically used by BIAB brewers) is more efficient that a thick mash.  Alternatively you can sparge if you want to completely eliminate this concern and possibly make it into a benefit (aggressive milling + sparging = better efficiency as compared with traditional methods).  As for me, additional ingredient costs are of minimal concern in my opinion.  This doesn’t amount to much, if anything for most beers and I would rather realize time savings on brew day.
  • Lifting the bag.  Depending on the beer, the amount of grain and the bag used, lifting a soaked bag of grain can be an issue.  If this is an issue for you, considering rigging up a (safe) pulley system to assist.
  • Temperature drift.  An uninsulated boil kettle probably drifts more than a well insulated cooler based mash tun.  Given the mass we’re talking about this is probably less of an issue than you may think.  However, it’s probably a fair point to make.  You can address that by adding insulation or, what I do is check temps half way through and add a little bit of heat.  This usually takes just a couple minutes.

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