Brew in a Bag Efficiency Calculator

What is Brew in a Bag (BIAB)?

Brew in a Bag (BIAB) is an all-grain brewing method that simplifies the mash and lautering process. Instead of a separate mash tun and hot liquor tank, you mash directly in your brew kettle using a fine mesh bag to hold the grains. This method reduces equipment costs, simplifies the brew day, and can achieve excellent efficiency with proper technique.

How to Use This BIAB Calculator

• Target final volume: Enter your desired batch size after boiling and cooling (typically 5-5.5 gallons for standard batches)
• Grain bill: Enter total grain weight in pounds — includes base malts and specialty grains
• Grain potential: Typical base malts are 36-38 ppg, crystal malts 34-35 ppg. Default 36 is a good starting point
• Brewhouse efficiency: The percentage of potential sugars extracted. Beginners: 65-70%, experienced: 70-75%, advanced: 75-80%
• Grain absorption: Amount of water absorbed by grains. Typical BIAB absorption is 0.08-0.10 gal/lb
• Boil-off rate: Depends on kettle diameter and heat source. Measure your system for accuracy
• Boil time: Standard is 60 minutes; adjust for your recipe
• Trub loss: Wort left behind in kettle with hops and break material

Understanding Your Results

• Strike Water Volume: Total water needed at the start of mash to achieve your target final volume
• Estimated Original Gravity: Calculated OG based on your inputs (e.g., 1.050 = 50 gravity points)
• Mash Efficiency: The efficiency of converting grain starches to sugar during the mash
• Total Gravity Points: Points per gallon × gallons = total sugar extracted
• Water Volume Breakdown: Shows each component: grain absorption, boil-off, trub loss, etc.

BIAB Efficiency Tips

• ✅ Mill your grains properly: A fine crush (but not flour) is essential for BIAB efficiency — ask for a "BIAB crush" at your homebrew shop
• ✅ Stir the mash: Stir every 15-20 minutes to prevent temperature stratification and improve extraction
• ✅ Maintain mash temperature: 148-158°F (64-70°C) depending on desired body. Use insulation or recirculation
• ✅ Mash longer: 60-90 minutes is standard; longer mashes can improve efficiency
• ✅ Squeeze the bag: Unlike traditional lautering, squeezing is encouraged in BIAB to recover absorbed wort
• ✅ Adjust water chemistry: Proper pH (5.2-5.6) improves enzyme activity and efficiency

Typical BIAB Efficiency Ranges

• Beginner: 60-68% — Learning the process, standard crush
• Intermediate: 68-75% — Fine crush, good technique, stirring
• Advanced: 75-82% — Optimized crush, recirculation, pH control, bag squeeze
• Maximum achievable: 85% — With double crush, extended mash, and perfect technique

Frequently Asked Questions

• What is a good BIAB efficiency? — 70-75% is considered good for most homebrewers. Focus on consistency rather than chasing maximum efficiency.
• How much water do I need for BIAB? — Start with strike volume = final volume + grain absorption + boil-off + trub loss. The calculator does this for you.
• Should I squeeze the grain bag? — Yes! Unlike traditional brewing, squeezing is recommended for BIAB to recover sugars and improve efficiency.
• What grain crush is best for BIAB? — A fine crush (credit card thickness) works best because the bag acts as a filter. Double crush at your LHBS.
• How do I measure my boil-off rate? — Boil 5 gallons of water for 60 minutes, measure the remaining volume. The difference is your boil-off rate.