Brew in a Bag (BIAB): The All-Grain Method That Skips the Expensive Gear

When I first looked into all-grain brewing, the equipment list made my eyes water. A mash tun with a false bottom. A hot liquor tank. A sparge arm. A grant. Silicone hoses everywhere. I was looking at $300-500 in gear before I even bought ingredients, and I needed a garage to set it all up in.

Then someone on a homebrew forum said four words that changed my brewing life: "Just do BIAB." Brew in a bag. One pot, one bag, same ingredients, same beer. I was skeptical — it sounded too simple to actually work. But after my first BIAB batch, I was converted. That was six years and probably 200 batches ago, and BIAB is still my primary method.

What Is BIAB, Exactly?

Traditional all-grain brewing separates the mash (soaking grain in hot water to convert starch to sugar) from the boil by using separate vessels and a process called sparging (rinsing the grain with additional hot water to extract more sugar).

BIAB collapses the entire process into one vessel. You heat your full volume of water in a single large pot, put all the grain in a large mesh bag, dunk the bag in the water, mash for an hour, pull the bag out, and boil in the same pot. No sparging. No separate mash tun. No complex plumbing.

What You Need

Here's the complete equipment list for BIAB. If you already brew extract, you probably have most of this:

• A large pot (10+ gallons for a 5-gallon batch): This is the key requirement. You need a pot big enough to hold your full pre-boil volume PLUS the grain. A 10-gallon pot is the minimum for 5-gallon batches. A 15-gallon pot gives you comfortable headroom. Bayou Classic and Concord make affordable options ($50-80)
• A BIAB bag: A fine-mesh nylon or polyester bag that fits inside your pot. The Brew Bag (thebrewinabag.com) is the gold standard — made to fit specific pot sizes, built-in handles, won't tear. About $30. Cheap voile fabric bags from Amazon work too but are less durable
• A heat source: Your stovetop might work for smaller batches, but 8+ gallons of water plus grain is heavy and slow to heat on a standard kitchen burner. A propane burner ($40-60) is a game-changer for full-volume BIAB
• A way to lift the bag: A wet grain bag weighs 15-25 lbs. You can lift it by hand (wear heat-resistant gloves), rig a pulley above your brew area, or set a cooling rack across the pot and let the bag drain on it
• A thermometer: You need to hit and hold your mash temperature. A basic dial thermometer ($10) works. An Inkbird or Thermapen ($15-30) is more accurate and faster

The BIAB Process: Step by Step

Step 1: Calculate your water volume

Unlike traditional all-grain where you split water between mash and sparge, BIAB uses your full volume in one vessel. You need to account for:

• Your target pre-boil volume (usually 6.5-7 gallons for a 5-gallon batch with a 60-minute boil)
• Grain absorption (roughly 0.12 gallons per pound of grain)

For a typical recipe with 11 lbs of grain: 6.75 + (11 x 0.12) = ~8.1 gallons of starting water.

Step 2: Heat the water

Heat your full water volume to a few degrees above your target mash temperature. When you add the room-temperature grain, the temperature will drop. For most pale beers, heat to about 156-158°F to hit a 152°F mash after dough-in. For darker or fuller-bodied beers, aim for 154-156°F post-grain.

Step 3: Dough in

Line your pot with the BIAB bag, making sure the bag drapes over the edges so it doesn't fall in. Slowly pour the crushed grain into the bag while stirring. Break up any clumps (dough balls) — they hide unconverted starch inside. Stir thoroughly until every bit of grain is wet and the mash is uniform.

Step 4: Mash for 60 minutes

Keep the mash temperature as steady as possible for 60 minutes. With a full volume of water, the thermal mass is large and the temperature drops slowly — maybe 2-4°F over the hour. If it drops more than 5°F, apply gentle heat while stirring. Some brewers wrap the pot in a sleeping bag or moving blankets for insulation.

Step 5: Pull the bag

After 60 minutes, lift the bag out of the pot. This is the awkward part. The bag is heavy, hot, and dripping. Options:

• Two-person lift: Have a buddy help you lift and hold the bag over the pot while it drains
• Cooling rack bridge: Set an oven cooling rack across the pot rim and rest the bag on it
• Pulley system: A basic rope-and-pulley from the hardware store, mounted above your brew area

Let the bag drain for 10-15 minutes. You can gently squeeze it to get more liquid out — the old "don't squeeze the bag" advice was about tannin extraction during sparging, which isn't a concern with BIAB's single-vessel approach.

Step 6: Boil and proceed as normal

From here, it's identical to extract brewing. Bring to a boil, add hops on schedule, cool, pitch yeast. The only difference is you made the wort yourself from grain instead of from a can of extract.

Improving Your BIAB Efficiency

Most BIAB brewers get 65-75% mash efficiency, compared to 75-85% for traditional three-vessel setups. Here's how to close the gap:

• Finer crush: The biggest single improvement. Double-crush or adjust the mill gap to 0.025-0.030 inches
• Stir the mash: Stir every 15 minutes during the mash. This redistributes enzymes and improves conversion
• Mash out at 168°F: Before pulling the bag, raise the temperature to 168°F. This reduces wort viscosity and helps it drain from the grain more completely
• Dunk sparge: After pulling the bag, dunk it in a second pot of 170°F water for 10 minutes. This rinses additional sugar from the grain. A partial sparge that adds 5-10 minutes and 5-8% efficiency

Common BIAB Questions

Can I do BIAB on my kitchen stovetop?

For 2.5-3 gallon batches, yes. For full 5-gallon batches, most kitchen stoves struggle to heat 8+ gallons of water in a reasonable time and maintain a vigorous boil. A propane burner outside is the practical solution for full-volume BIAB.

Will the bag melt or tear?

Not if you use a proper BIAB bag. Quality bags are made from heat-resistant polyester or nylon rated to 300°F+. Just don't let the bag touch the bottom of the pot directly while applying heat — it won't melt, but the grain on the bottom can scorch. Lift the bag slightly or stir while heating.

How does BIAB beer compare to traditional all-grain?

In blind taste tests, there's no detectable difference. Seriously. Multiple homebrew clubs have done side-by-side comparisons and the results are consistent: BIAB produces beer that's indistinguishable from traditional three-vessel all-grain. The wort doesn't care how you separated it from the grain.