Brew in a Bag is what happened when Australian homebrewers in the early 2000s asked a simple question: what if we did the whole mash in the boil kettle and just lifted the grain out with a bag? The result was a method that requires less equipment than traditional all-grain brewing, fits in a single-vessel setup, and produces genuinely excellent beer. If you’ve been brewing with extract and want to make the jump to all-grain without buying a second vessel, BIAB is the smartest route there is. Northern Brewer sells BIAB starter kits that include the bag and a compatible kettle.
What Makes BIAB Different from Traditional All-Grain?
Traditional three-vessel all-grain brewing uses a separate mash tun (often a cooler), a hot liquor tank for sparge water, and a boil kettle. Grain is mashed in the mash tun, rinsed with hot sparge water, and the resulting wort is collected in the kettle for boiling.
BIAB combines all of this into one vessel. The fine-mesh bag holds your grain inside the boil kettle, you mash directly in the water you’ll boil, and at the end of the mash you simply lift the bag out. There’s no vorlauf, no fly sparging, no separate transfer — just one pot, one bag, one less hour, and one fewer thing to clean.
The American Homebrewers Association recognizes BIAB as a fully legitimate all-grain method, and many award-winning homebrew competition entries have been made with it.
Equipment You Need
The beauty of BIAB is the short equipment list:
- A large kettle — You need enough volume to hold your full pre-boil water plus grain. For 5-gallon batches, a 10-gallon (38L) kettle is comfortable. A 7.5-gallon kettle works for smaller grain bills.
- A fine-mesh BIAB bag — Sold at homebrew shops; sized to fit your kettle and hang over the rim. The mesh should be fine enough to hold back fine grain flour.
- A reliable heat source — Propane burner outdoors or a strong electric stove; you’re heating a lot of water.
- A thermometer — Accuracy to ±1°F matters here. Digital probe thermometers are ideal.
- A way to suspend and drain the bag — A pulley system, a ladder, or just holding the bag over the kettle for 5–10 minutes while it drains. A colander balanced on the kettle rim works well.
That’s it. No cooler mash tun, no second vessel, no pump. For an overview of what gear matters for brewing in general, see Homebrewing Equipment for Beginners: The Essential Checklist.
The BIAB Method Step by Step
Step 1 — Prepare and Heat Full Volume Water
BIAB uses a “full volume” mash — all of your pre-boil water goes into the kettle before you add the grain. This is different from traditional mashing where you calculate a specific strike water volume and add sparge water separately. For a 5-gallon batch with 12% boil-off, you’d heat about 7–7.5 gallons.
Heat your water to your strike temperature. This will be 5–10°F above your target mash temperature because the grain will cool it on contact. For a 152°F (67°C) mash, heat to 157–162°F (69–72°C).
Step 2 — Add Grain and Mash
Lower your BIAB bag into the kettle so it hangs over the rim, then slowly pour in your milled grain while stirring constantly to prevent dough balls. Once all grain is in, check your temperature and adjust if needed. Cover the kettle (a lid, a towel, or a reflective thermal blanket all work) and mash for 60 minutes.
Check temperature at 15 and 30 minutes and apply heat briefly if you’ve dropped more than 2–3°F (1–2°C). Most setups on a propane burner lose only 1–2°F per hour.
Step 3 — Lift, Squeeze, and Drain
After the 60-minute mash rest, lift the bag and allow it to drain freely for 5–10 minutes — position it over the kettle so the wort falls back in. Once draining slows, you can squeeze the bag firmly to recover additional wort. Some traditional brewers avoid squeezing for fear of tannin extraction, but research and practical homebrew experience has shown that squeezing a properly mashed grain bag does not produce noticeable astringency at normal mash temperatures. How to Brew by John Palmer discusses this directly and notes that the concern about squeezing is largely a myth.
Step 4 — (Optional) Mini Sparge
A simple way to boost your efficiency: heat 1–2 gallons of water to 168°F (76°C) and pour it over the suspended bag into a separate container, then add this to your kettle. This “dunk sparge” or “pour-over sparge” recovers sugars left behind in the grain and can improve typical BIAB efficiency from 65–70% up to 75–80%.
Step 5 — Bring to a Boil and Brew as Normal
Once the bag is out, proceed exactly like any other brew. Bring to a rolling boil, add hops according to your schedule, add finings in the final 15 minutes, and chill your wort. The boil, chilling, fermenter transfer, and fermentation are identical to any other brewing method.
BIAB Efficiency: What to Expect
Traditional three-vessel all-grain setups typically achieve 70–80% brewhouse efficiency. BIAB efficiency, depending on crush and technique, typically runs 65–75% without a sparge and can reach 75–82% with a mini-sparge. This means you may need slightly more grain than a traditional recipe specifies — most BIAB brewers apply a 5–10% grain bill increase or use an efficiency-correcting brewing software.
Brewer’s Friend and Beersmith both have BIAB efficiency settings that automatically adjust grain bills for your typical system efficiency.
BIAB Tips for Better Results
- Mill finer than traditional all-grain — Because there’s no sparge to worry about, a slightly finer crush improves conversion efficiency without causing stuck sparges. MoreBeer offers grain milling services at their retail locations if you don’t own a mill.
- Allow a longer mash rest — 75–90 minutes is common in BIAB to ensure full conversion with the single infusion.
- Insulate your kettle — A towel, sleeping bag, or neoprene kettle wrap dramatically reduces temperature loss during the mash.
- Keep notes on efficiency — Your first few BIAB batches will establish your baseline efficiency. Once you know it, recipe design becomes much more predictable.
BIAB vs. Extract: Is It Worth the Switch?
BIAB gives you full control over your fermentables — you can use any grain, hit any mash temperature, and build completely original recipes rather than working from a base of extract. The flavor improvements are real and noticeable in side-by-side comparisons, especially for clean, malt-forward styles. The Siebel Institute teaches that full mash control is the foundation of repeatable, professional-quality brewing.
The additional time cost over extract brewing is roughly 60–90 minutes (the mash plus bag-out). For most homebrewers, that trade-off is well worth making.
The Brew Professor Takeaway
BIAB removes almost every barrier between you and full all-grain brewing. One pot, one bag, one session. Your efficiency will be a few points lower than a three-vessel setup, but the simplicity, the cleanup ease, and the immediate upgrade in recipe flexibility make it the recommended first step into all-grain brewing for anyone brewing 5-gallon batches on a stovetop or with a single propane burner. Once you’ve done a BIAB brew, you’ll wonder why you ever worried about the jump.
