How to brew 'boil in a bag' beer

Boil in a bag brewing is one of the most straightforward ways to make beer at home. 

It uses a large nylon or muslin bag to contain the grains and hops during the mash and boil. 

The bag keeps solids contained, allowing flavor and sugars to extract into the wort while reducing mess and equipment cleaning.

The bag sits directly in the hot water, letting enzymes convert starches into fermentable sugars. When the boil is done, you simply lift the bag out, drain, and ferment the wort separately. 

This method gives full-grain flavor without needing a complex setup or multiple vessels.

Originally developed by homebrewers in Australia in the 1990s, “BIAB” became a hit across the brewing world for its affordability and ease. It has since become a trusted starting point for thousands of new brewers — and plenty of Kiwis picked it up too.

Pros of Boil in a Bag Brewing

1. Simplicity: It requires minimal equipment and can be done with a single kettle, making it ideal for small spaces or beginners.
2. Flexibility: You can brew almost any style with BIAB. From hoppy pale ales to dark stouts, it handles all-grain recipes with ease.
3. Easy Cleanup: Since all the grain and hops stay in the bag, cleaning is fast and painless. No more grain sludge in your tap or chiller.

Cons and Limitations

1. Limited Batch Size: Bag size restricts how much grain you can use, which limits batch volume unless you have a large kettle.
2. Lower Efficiency: Because water circulation is restricted, sugar extraction can be slightly lower. Proper stirring and mash management help offset this.
3. Bag Quality: Cheap bags can leach flavors or tear. Always use a high-quality, heat-safe nylon or muslin bag made for brewing.

Step-by-Step BIAB Brewing Guide

1. Line your kettle with the grain bag and secure it with clips.
2. Fill with strike water at the target temperature for your mash.
3. Stir in crushed grains to prevent dough balls and ensure full hydration.
4. Close the lid and insulate the kettle to hold mash temperature for 30–60 minutes, stirring occasionally.
5. Lift the bag carefully and allow it to drain. A pulley or winch helps. Optionally sparge with 75°C water to rinse remaining sugars. Use heat-resistant gloves for safety.
6. Proceed with the normal boil, hop additions, and standard brewing steps to finish the batch.

Tips for a Great BIAB Brew

Use a sturdy bag: Choose high-quality nylon or muslin that resists tearing and won’t impart flavors.

Crush your grains properly: A consistent, coarse crush improves extraction and prevents stuck runoff. See this grain mill guide for setup advice.

Sparge smartly: If sparging, use 75°C water and pour evenly over the bag. This boosts yield without leaching tannins. Gentle stirring helps efficiency.

Watch the boil: Foam rises quickly in BIAB setups. Keep an eye on heat and use a spray bottle or fan to control boilovers.

Sanitize everything: Always sanitize your equipment and brewing kettle before and after use to avoid off-flavors or infections.

Does Boil in a Bag Make Good Beer?

Absolutely. BIAB beers have won major competitions, proving this simple method can produce award-winning results.

• In 2017, Australian brewer Tim Johnson took first in the Strong Ale category with a Belgian dark strong ale using BIAB.
• In 2016, Doug Piper won the National Homebrew Competition’s Belgian Strong Ale category with a golden strong ale made via BIAB.
• In 2018, New Zealander Luke Nicholas won top honors for a Pale Ale brewed using the same approach.

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