Why does mill gap matter?

The grain crush determines how much starch is exposed to enzymes during mashing. Too coarse means poor efficiency. Too fine can cause stuck sparges (except BIAB). Finding the right balance maximises extract while maintaining good lauterability.

How do I measure my mill gap?

Use feeler gauges inserted between the rollers. Most homebrewing mills have an adjustment knob or bolt. Set the gap, lock it in place, and run a handful of grain through to check the crush quality visually.

What should a good crush look like?

Ideally, every grain kernel should be cracked open with the husk relatively intact. You should see broken endosperm (white starchy bits) but not flour-like powder. The husks should be torn but not shredded into tiny pieces.

Does mill gap affect efficiency?

Yes, significantly. A finer crush exposes more starch to enzymes, increasing conversion efficiency. However, too fine a crush can cause stuck sparges. The optimal gap balances efficiency with easy lautering. BIAB brewers can use finer gaps (0.6-0.8mm) since there is no sparge.

How often should I adjust my mill?

Once set correctly, most mills hold their gap setting well. Check the gap if you notice a sudden change in efficiency. Different grain types may benefit from slightly different gaps, but most brewers use a single setting for all grains.

BrewCalcs

Grain Mill Gap Calculator

Find the optimal mill gap setting for your grain type and mash system.

Mash Method

Grain Type

How We Calculate This

Gap Recommendations

Mill gap depends on your sparging method. BIAB can use the finest crush (0.8mm) since the bag prevents stuck sparges. Batch sparging needs a medium crush (1.0mm), and fly sparging needs the coarsest (1.2mm) to maintain a filter bed.

Frequently Asked Questions

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Last updated: 2025-02-20

All calculations are estimates. Always verify values and adjust based on your equipment and ingredients.