Buying a grain mill and grist case for a brewpub

Why mill on site at all

Many new brewpubs plan to buy pre-milled malt. It saves space and a machine. The trouble is that crushed malt stales faster than whole grain and picks up moisture quickly, especially in a coastal city in the monsoon. Damp, stale grist gives lower extract and duller flavour.

Milling on site lets you buy whole malt, store it longer and set the crush for your own lauter tun. For a brewpub brewing more than once or twice a month, a mill usually pays for itself in yield and flexibility.

Two rollers, four rollers or more

The aim of milling is to crack each kernel and break the starchy inside into grits while keeping the husk as whole as possible. The husk forms the filter bed in the lauter tun. Shred it and the run-off slows to a crawl.

• Two-roller mills crush in one pass. They suit most brewpubs up to about 10 hl. The gap is typically set somewhere around 1.0 to 1.3 mm and tuned by checking the grist.
• Four-roller mills crack the grain, separate the husk, then crush the grits again. They give better husk preservation and higher yield at larger scales.
• Six-roller and wet mills belong in larger production breweries.

For a brewpub, a sturdy two-roller mill with adjustable gap and hardened, knurled rollers is the usual choice.

Sizing the mill and the grist case

Work out the malt you need per brew. A 1,000 litre batch at 12 °Plato needs about 126 kg of extract, since 1,000 litres at that gravity weighs about 1,048 kg and 12% of that is sugar. At around 60% of the malt's weight ending up as extract in the kettle, which is typical for a small brewhouse, that is roughly 210 kg of malt.

Choose a mill that can crush that in about an hour or less, so milling does not hold up the brew day. A grist case should hold at least one full brew, with some headroom. Milled malt is bulky. Allow roughly half a cubic metre for 210 kg plus space so the grist does not pack. If you brew twice a day, size it for two.

Dust is the safety issue

Malt dust is combustible. A fine cloud in an enclosed space with a spark can ignite. That is why larger malt handling systems are designed with explosion protection. In a brewpub, the practical steps are simple but not optional:

• Keep the mill in a separate room or enclosure, away from the kitchen and open flames.
• Earth the mill, the grist case and any metal conveying to prevent static.
• Fit dust extraction or at least a sealed hopper and grist case.
• Clean up dust daily rather than letting it build up on ledges.
• Use motors and switches suited to dusty areas.

Dust also attracts insects and rodents. Our guide to pest control in a grain store covers the rest.

Getting grist to the mash tun

In the smallest brewpubs, a brewer carries buckets of grist up a ladder. It works, but it is dusty and hard on backs. A step up is a grist case above the mash tun so grist falls by gravity through a hydrator, where it mixes with hot water as it enters. An auger or flexible screw conveyor moves grist from a mill on the floor to a mash tun on a platform.

Hydrators matter. Dumping dry grist onto hot water makes dough balls, lumps of dry flour inside a wet shell. Those lumps hold starch that never converts. A good hydrator or premasher wets the grist evenly as it goes in.

Setting and checking the crush

Once installed, set the gap and check the grist by eye and by sieve. You want most kernels cracked, the husks largely intact and little flour. Adjust in small steps and track your brewhouse yield and run-off time. Write the gap setting down for each malt, since wheat and some specialty malts behave differently.

Rollers wear over the years, which slowly changes the crush. A yield that drifts down over months is often a mill, not a recipe. That kind of link between kit and numbers is what we teach founders to watch.

Where the mill goes in the layout

Put the mill near the malt store and away from the kitchen, the bar and the customers. Noise and dust do not suit a dining room. Think about the route malt takes from the delivery van to the store, the mill and the mash tun. Our guide to brewpubs versus microbreweries shows how space shapes these choices.

Before you order

Write down your batch size, your target gravity and how many brews you plan per day. Work out malt per brew using the sum above. Ask suppliers for mill capacity in kg per hour, gap adjustment range and dust control options. Then measure the room where you plan to put it.

Common questions

What roller gap should a brewery mill use?

For a two-roller mill, somewhere around 1.0 to 1.3 mm is a common starting point. Tune it by checking the grist and your lauter run-off, since malt size and lauter design vary.

Can a brewpub buy pre-milled malt instead?

Yes, but milled malt stales faster and picks up moisture, especially in humid weather. Milling on site gives fresher grist and lets you set the crush for your system.

Is malt dust dangerous?

Yes. Fine malt dust can ignite. Keep the mill in an enclosed area, earth the equipment, control dust and keep it away from flames.